Cisco AVVID Network Infrastructure

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Cisco AV V ID N et w ork Inf rast ruct ure Ent erprise Qualit y of Service D esign Solutions Reference Netw ork Design August, 2002

Corporat e Headquart ers Cisco System s, Inc. 170 West Tasm an Drive San Jose, CA 95134-1706 USA http://w w w .cisco.com Tel: 408 526-4000 800 553-NETS (6387) Fax: 408 526-4100

Custom er Order Num ber: 956467

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C O N T E N T S About this Document

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Intended Audience

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Document Organization

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Document Conventions

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Obtaining Documentation W orld W ide W eb

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Documentation CD-ROM

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Ordering Documentation

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Documentation Feedback

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Obtaining Technical Assistance Cisco.com

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Technical Assistance Center Cisco TAC W eb Site

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Cisco TAC Escalation Center

CH A P TER

1

Overview

xv

1-1

W hy is Quality of Service Required for AVVID? Understanding QoS Loss Delay

1-1

1-1

1-2 1-3

Delay Variation

1-3

Quality of Service Requirements for Voice Voice Traffic

1-3

1-4

Voice Control Traffic

1-5

Quality of Service Requirements for Video Streaming Video Video conferencing

1-6

1-6 1-7

Quality of Service Requirements for Data

1-7

Relative Priority vs. Over-Engineering Bandw idth Provisioning Determining the Classes of Data Traffic Provisioning for Important Data Traffic Reactive vs. Proactive Policies

1-9 1-9

1-10

Non-Technical QoS Considerations of Data Service-Provider QoS Requirements

1-8

1-10

1-11

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Contents

W hat is the Quality of Service Toolset? Classification Tools

1-12

1-12

Class of Service

1-13

Type of Service and Differentiated Services Code Points Per-Hop Behaviors

1-14

Netw ork-Based Application Recognition Classification Equivalents Voice Bearer Traffic

1-16

Voice Control Traffic

1-16

Video Conferencing Streaming Video

1-15

1-16 1-16

M ission-Critical Data

1-17

Less-Than-Best-Effort Data Best-Effort Data

1-17

1-17

1-17

Class-Based W eighted-Fair Queueing Low -Latency Queueing Scheduling Recommendations Queue Scheduling

1-22

Number of Queues

1-22

Provisioning Tools

1-20

1-22

1-22

Policing and Shaping Tools Link-Efficiency M echanisms Call Admission Control M anagement Tools 2

1-18

1-19

W eighted-Random Early Detect

CH A P TER

1-14

1-14

Classification Recommendations

Scheduling Tools

1-13

1-23 1-23

1-26

1-26

QoS Considerations W hen Connecting End-Points to an AVVID Netw ork Overview

2-1

2-1

The Trusted Edge IP Telephony IP Phones

2-2

2-2 2-2

CallM anager

2-2

VoIP Gatew ays H.323

2-3

M GCP

2-3

2-3

Classification for Non-marking Applications

2-3

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Video

2-3

Video Conferencing Streaming Video

2-4 2-4

M ission-Critical Applications DLSW +

2-4

Less-than-Best-Effort Summary

CH A P TER

3

2-4

2-5

2-5

QoS in an AVVID-Enabled Campus Netw ork Overview

3-1

Delay Variation

3-2

Transmit Buffer Congestion QoS Toolset

3-1

3-2

3-4

Classification Scheduling

3-4 3-5

Server Farm Sw itch Selection Voice Bearer Traffic

3-6

3-7

Voice over IP Call Control Skinny Protocol

3-10

H.323 Protocol M GCP

3-10

3-11

3-11

Verifying the ACLs M ission-Critical Data

3-12 3-12

Selecting an Access-Layer Sw itch

3-14

Catalyst 6500 as an Access-Layer Sw itch Enabling QoS

3-15

3-17

Configuring IP Phone Port Queuing

3-17

Configuring the Uplink to the Distribution Sw itch Verifying the Configuration

3-18

3-19

Catalyst 4000 as an Access-Layer Sw itch

3-21

Catalyst 4000 w ith Supervisor III

3-22

Catalyst 4000 w ith Supervisor II

3-29

Catalyst 3524-PW R XL as an Access-Layer Sw itch Configuring IP Phone Port Queuing

3-31

3-32

Configuring the Uplink Interface to the Distribution Sw itch Catalyst 3550 as an Access-Layer Sw itch Enabling QoS

3-33

3-33

3-34

M odifying the CoS-to-DSCP M appings Enabling Priority Queuing

3-34

3-35

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Contents

Configuring ACLs

3-35

Configuring Access-Layer Phone Support

3-36

Configuring the Uplink to the Distribution Sw itch Verifying the Configuration

3-37

Catalyst 2950 as an Access-Layer Sw itch

3-38

M odifying the CoS-to-DSCP M appings Configuring ACLs

3-36

3-39

3-40

Configuring Access-Layer Phone Support

3-40

Configuring the Uplink to the Distribution Sw itch Verifying the Configuration

3-41

3-41

Selecting a Distribution-Layer Sw itch

3-42

Catalyst 6500 (w ith Catalyst OS) as a Distribution-Layer Sw itch

3-42

Configuring the Distribution Layer VoIP Control Traffic Transmit Queue Configuring the Distribution Layer w ith a Layer 3 Sw itch

3-43

Configuring the Distribution Layer w ith a Layer 2 Sw itch

3-44

Verifying the Configuration

3-45

Catalyst 6500 (w ith Native IOS) as a Distribution-Layer Sw itch Enabling QoS

3-47

3-47

Configuring the Distribution Layer VoIP Control Traffic Transmit Queue Configuring the Distribution Layer w ith a Layer 3 Sw itch

3-48

Configuring the Distribution Layer w ith a Layer 2 Sw itch

3-49

Verifying the Configuration

Configuring Priority Queuing Configuring ACLs

3-52

3-53

3-53

Configuring Service Policy

3-54

Configuring CoS or DSCP Trust Verifying the Configuration

3-54

3-55

Catalyst 3550 as a Distribution-Layer Sw itch

3-58

3-58

M odifying the CoS-to-DSCP M apping Enabling Priority Queuing Configuring ACLs

3-59

3-59

3-59

Configuring CoS or DSCP Trust Verifying the Configuration Summary

3-51

3-52

M odifying the CoS-to-DSCP M apping

Enabling QoS

3-48

3-51

Catalyst 4000 w ith Supervisor III as a Distribution-Layer Sw itch Enabling QoS

3-43

3-60

3-61

3-63

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Contents

CH A P TER

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QoS in an AVVID-Enabled W ide-Area Netw ork Overview

4-1

4-1

QoS Toolset

4-2

Classification Provisioning

4-2 4-2

Policers and Shapers

4-2

Link-Fragmentation and Interleaving TX Ring

4-3

4-3

M odular QoS Command-Line Interface

4-4

QoS Recommendations for W AN Aggregation Routers

4-4

Classifying and Provisioning for Voice on the W AN Edge

4-4

Classifying and Provisioning for Video on the W AN Edge

4-6

Classifying and Provisioning for Data on the W AN Edge Link-Specific W AN QoS Recommendations High-Speed Point-to-Point Links

4-9

Slow -Speed Point-to-Point Links

4-10

High-Speed Frame Relay Links

4-9

4-11

Distributed-Platform High-Speed Frame Relay Links Slow -Speed Frame Relay Links 4-18

Slow -Speed ATM Links

4-19

ATM -to-Frame Relay Recommendations ISDN Recommendations Summary Configurations

4-21

4-26 4-28

4-28

Remote LAN Edge for Voice

4-28

Remote LAN Edge for Video

4-29

Remote LAN Edge for Data Output Policies Input Policies

4-30

4-30 4-30

Summary Configuration Verifying QoS

4-17

4-24

QoS Recommendations for Remote Branch Routers W AN Edges

4-14

4-15

Distributed-Platform Slow -Speed Frame Relay Links High-Speed ATM Links

4-6

4-32

4-34

show policy

4-34

show policy interface Example 1

4-36

Example 2

4-40

show interface

4-42

4-36

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show queue

4-43

show frame-relay pvc show atm bundle

4-43

4-47

show policy interface atm show atm vc show atm pvc

CH A P TER

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4-47

4-47 4-48

QoS in a SOHO Virtual Private Netw ork for IP Telephony Overview QoS Toolset

5-1 5-2

Classification

5-2

Classification of Voice Bearer traffic

5-2

Classification of Voice Signaling Traffic Scheduling Provisioning

5-3

5-3 5-3

TX Ring Sizing

5-3

Link Fragmentation and Interleave

5-3

Fragment Sizing for M LPPP over ATM Traffic Shaping

5-3

5-4

Bandw idth Calculation Solutions

5-5

5-6

Application of QoS to DSL in a SOHO Environment One and Tw o Box DSL Solution Third-Party M odem Solution

5-9

One and Tw o Box Cable Solution Third-Party M odem Solution

Voice over ISDN

CH A P TER

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5-13 5-14

5-14

5-15

5-16

QoS w ith M PLS in an AVVID-Enabled Netw ork Overview

5-10

5-11

Application of QoS over Other Technologies Last M ile W ireless, IDSL, etc.

5-6

5-7

Application of QoS to Cable in a SOHO Environment

Summary

5-1

6-1

6-1

M PLS VPN Architecture

6-2

M PLS M odes of Operation M PLS Labels

6-2

6-3

M PLS Label Stack

6-3

Placement of Labels by M ode

6-4

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M PLS VPN QoS

6-5

Considerations for M PLS VPN QoS Convergence

6-5

After a Link Failure

6-5

After a Link Recovery Redundancy

6-5

6-6

6-6

Using IP M ulticast over M PLS VPNs Implementing M PLS VPN QoS CE Routers

6-8

PE Routers

6-10

P Routers

A P PEN D I X

A

6-7

6-8

6-13

Reference Information DSCP Equivalents

A-1 A-1

Catalyst 6500 Linecards and Queuing M echanisms M ission-Critical Applications W ell-Know n Ports DLSW + Considerations W hen to Enable cRTP

A-5

Cisco Public Documentation Cisco Internal Documentation

A-6

A-6

Cisco Limited-Access Information

Other External Sites

A-3

A-4

W eb Sites w ith Additional Information

RFCs from the IETF

A-2

A-7

A-7

A-8 A-8

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About this Document This document is designed to present an overview of the use of Quality of Service (QoS) in a variety of Cisco AVVID environments.

Intended Audience This document is intended for customers and Enterprise Systems Engineers (SEs) who has recently become involved with the QoS aspects of a Cisco AVVID network and who may be unfamiliar with the deployment choices available to an Enterprise customer. It provides in-depth design and configuration recommendations for the implementation of QoS to successfully meet the loss, delay, and delay variation (jitter) requirements of voice over IP, video over IP, and mission-critical data in a variety of environments.

Document Organization This document contains the following chapters: Chapter or Appendix

Description

Chapter 1, “Overview”

Provides an overview of QoS, the need for QoS in an AVVID network, and the QoS toolset.

Provides information about implementing QoS at the network edge. Chapter 2, “QoS Considerations When Connecting End-Points to an AVVID Network” Chapter 3, “QoS in an AVVID-Enabled Campus Network”

Discusses the need for QoS in a campus environment and provides guidelines and examples for implementation.

Chapter 4, “QoS in an AVVID-Enabled Wide-Area Network”

Discusses the need for QoS in a wide-area network (WAN) and provides guidelines and examples for implementation.

Chapter 5, “QoS in a SOHO Discusses the need for QoS in a small office, home office (SOHO) Virtual Private Network for environment and provides guidelines and examples for implementation. IP Telephony”

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About this Document Document Conventions

Chapter or Appendix

Description

Chapter 6, “QoS with MPLS Discusses the nuances of implementing QoS with MPLS in an AVVID in an AVVID-Enabled network. Network” Appendix A, “Reference Information”

Note

Provides reference information, such as equivalence tables and URLs for referenced documents.

The chapters of this document contain references to other documents. These references are included as tips in the text. The URL for each referenced document is located in Appendix A “Reference Information.” In some cases, an internal document is referenced. For copies of internal documents, please see your Cisco Systems representative.

Document Conventions This guide uses the following conventions to convey instructions and information: Table 1

Document Conventions

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Variables for which you supply values.

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Keywords or arguments that appear within square brackets are optional.

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A choice of required keywords appears in braces separated by vertical bars. You must select one.

screen font

Examples of information displayed on the screen.

boldface screen

Examples of information you must enter.

font




Nonprinting characters, for example passwords, appear in angle brackets.

[

]

Default responses to system prompts appear in square brackets.

Note

Timesaver

Tips

Means reader take note. Notes contain helpful suggestions or references to material not covered in the manual.

Means the described action saves time. You can save time by performing the action described in the paragraph.

Means the following information will help you solve a problem. The tips information might not be troubleshooting or even an action, but could be useful information, similar to a Timesaver.

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About this Document Obtaining Documentation

Caution

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Obtaining Documentation The following sections explain how to obtain documentation from Cisco Systems.

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About this Document Obtaining Technical Assistance

To submit your comments by mail, use the response card behind the front cover of your document, or write to the following address: Cisco Systems Attn: Document Resource Connection 170 West Tasman Drive San Jose, CA 95134-9883 We appreciate your comments.

Obtaining Technical Assistance Cisco provides Cisco.com as a starting point for all technical assistance. Customers and partners can obtain documentation, troubleshooting tips, and sample configurations from online tools by using the Cisco Technical Assistance Center (TAC) Web Site. Cisco.com registered users have complete access to the technical support resources on the Cisco TAC Web Site.

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Priority level 4 (P4)—You need information or assistance concerning Cisco product capabilities, product installation, or basic product configuration.

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About this Document Obtaining Technical Assistance

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Priority level 2 (P2)—Your production network is severely degraded, affecting significant aspects of business operations. No workaround is available.

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C H A P T E R

1

Overview This chapter provides an overview of Quality of Service (QoS) and its uses. This chapter provides high-level answers to the following questions:

Note

•

Why is Quality of Service Required for AVVID?

•

What is the Quality of Service Toolset?

This chapter contains references to other documents. These references are included as tips in the text. The URL for each referenced document is located in Appendix A, “Reference Information.” In some cases, an internal document is referenced. For copies of internal documents, please see your Cisco Systems representative.

W hy is Quality of Service Required for AVVID? The key enabling technology for network convergence in the Architecture for Voice, Video, and Integrated Data (AVVID) is QoS. This is because voice, video, and mission-critical data have stringent service requirements from the network infrastructure. These requirements supersede the requirements of generic data traffic. If voice, interactive-video, and mission-critical data are not given priority service from network devices, then the quality of these important applications would quickly degrade to the point of being unusable.

Understanding QoS QoS is defined as the measure of performance for a transmission system that reflects its transmission quality and service availability. Service availability is a crucial foundation element of QoS. Before any QoS can be implemented successfully, the network infrastructure must be designed to be highly available. The transmission quality is determined by the following factors: •

Loss

•

Delay

•

Delay Variation

There are many points in AVVID networks where QoS mechanisms are required to manage loss, delay, and delay variation. Figure 1-1 illustrates areas where QoS mechanisms are required to control the impact of loss, delay, and delay variation on voice performance.

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Chapter 1

Overview

W hy is Quality of Service Required for AVVID?

Figure 1-1

Areas Where QoS is Needed

Central campus

Remote branch

M

Si

WAN

IP

Si

IP

Establish Trust Boundary Layer 2 (802.1p) to Layer 3 (DSCP) classification Layer 3 (DSCP) to Layer 2 (802.1p) classification Layer 2 or Layer 3 classification where required-service policies CoS/DSCP to queue entry criteria Multiple queues and queue scheduling (priority or high)

QoS - Campus Dist.

QoS - WAN

Establish Trust BoundaryTrust DSCP or CoS from Access Layer

Low-latency queuing

Layer 2 (802.1p) to Layer 3 (DSCP) classification Layer 3 (DSCP) to Layer 2 (802.1p) classification Layer 2 or Layer 3 classification where required-service policies

Data traffic queue provisioning Link Fragmentation and interleave Traffic shaping Admission control

QoS - Branch Map L3 DSCP to L2 CoS via sevice policy out and 802.1q trunk Layer 2 (802.1p) to Layer 3 (DSCP) classification Layer 3 (DSCP) to Layer 2 (802.1p) classification Layer 2 or Layer 3 classification where required-service policies

CoS/DSCP to queue entry criteria

CoS/DSCP to queue entry criteria

Multiple queues and queue scheduling (priority or high)

Multiple queues and queue scheduling (priority or high)

81099

QoS - Campus Access

Loss Loss (or packet loss) is a comparative measure of packets faithfully transmitted and received to the total number that were transmitted. Loss is expressed as the percentage of packets that were dropped.

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Chapter 1

Overview W hy is Quality of Service Required for AVVID?

Delay Delay (or latency) is the amount of time it takes a packet to reach the receiving endpoint after being transmitted from the sending endpoint. This time period is termed the “end-to-end delay” and can be broken into two areas: fixed network delay and variable network delay. Fixed network delay includes encoding/decoding time (for voice and video), as well as the finite amount of time required for the electrical/optical pulses to traverse the media en route to their destination. Variable network delay generally refers to network conditions, such as congestion, that may affect the overall time required for transit. In data networks carrying voice, there are three types of delay: •

Packetization delay, which is the amount of time that it takes to sample and encode the analog voice signals and turn them in to packets.

•

Serialization delay, which is the amount of time that it takes to place the bits of the data packets onto the physical media.

•

Propagation delay, which is the amount of time it takes to transmit the bits of a packet across the physical wire.

Delay Variation Delay variation (or jitter) is the difference in the end-to-end delay between packets. For example, if one packet required 100 ms to traverse the network from the source-endpoint to the destination-endpoint and the following packet required 125 ms to make the same trip, then the delay variation is calculated as 25 ms. Each end station in a VoIP or Video over IP conversation has a jitter buffer. Jitter buffers are used to smooth out changes in arrival times of data packets containing voice. A jitter buffer is dynamic and can adjust for up to a 30 ms average change in arrival times of packets. If you have instantaneous changes in arrival times of packets that are outside of the capabilities of a jitter buffer’s ability to compensate you will have jitter buffer over-runs and under-runs. •

A jitter buffer under-run occurs when arrival times of packets increases to the point where the jitter buffer has been exhausted and contains no packets to be processed by the DSPs when it is time to play out the next piece of voice or video.

•

A jitter buffer over-run occurs when packets containing voice or video arrive faster than the jitter buffer can dynamically resize itself to accommodate. When this happens packets are dropped and when it is time to play out the voice or video samples contained in the dropped packets quality is degraded.

Quality of Service Requirements for Voice When addressing the QoS needs of voice traffic, keep the following in mind: •

Loss should be no more than 1%.

•

One-way latency should be no more than 150-200 ms.

•

Average jitter should be no more than 30 ms.

•

21-106 kbps of guaranteed priority bandwidth is required per call (depending on the sampling rate, codec and Layer 2 overhead).

•

150 bps (+ Layer 2 overhead) per phone of guaranteed bandwidth is required for Voice Control traffic.

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Chapter 1

Overview

W hy is Quality of Service Required for AVVID?

Voice quality is directly affected by all three QoS quality factors: loss, delay, and delay variation. Loss causes voice clipping and skips. The industry standard codec algorithms used in Cisco Digital Signal Processor (DSP) can correct for up to 30 ms of lost voice. Cisco VoIP technology uses 20 ms samples of voice payload per VoIP packet. Therefore, for the codec correction algorithms to be effective, only a single Real Time Transport (RTP) packet can be lost during any given time. If two successive voice packets are lost, the 30ms correctable window is exceeded and voice quality begins to degrade. Delay can cause voice quality degradation if it is above 200 ms. If the end-to-end voice delay becomes too long (for example, 250 ms), the conversation begins to sound like two parties talking on over a satellite link or even a CB radio. The ITU standard for VoIP (G.114) states that a 150 ms one-way delay budget is acceptable for high voice quality. The Cisco Technical Marketing Team has shown that there is a negligible difference in voice quality scores using networks built with 200 ms delay budgets. With respect to delay variation, there are adaptive jitter buffers within Cisco IP Telephony devices. However, these can usually only compensate for 20 to 50 ms of jitter. Implementing QoS is a means to use bandwidth efficiently, but not a blanket substitute for bandwidth itself. When an enterprise is faced with ever increasing congestion, a certain point is reached where QoS alone will not solve bandwidth requirements. At such a point, nothing short of additional bandwidth will suffice. The following sections provide guidelines that can help you determine when this point is reached.

Voice Traffic The bandwidth consumed by VoIP streams is calculated by adding the packet payload and all headers (in bits), then multiplying by the packet rate per second (default of 50 packets per second). Table 1-1 details the bandwidth per VoIP flow at a default packet rate of 50 packets per second (pps) and at 33 pps. This does not include Layer 2 overhead and does not take into account any possible compression schemes, such as compressed Real-time Transport Protocol (cRTP). The Service Parameters menu in Cisco CallManager Administration can be used to adjust the packet rate.

Note

Although it is possible to configure the sampling rate above 30 ms, this usually results in very poor voice quality. Table 1-1

Voice Bandw idth (w ithout Layer 2 overhead)

Bandw idth Consumption

Sampling Rate

Voice Payload in Bytes

Packets per Second

Bandw idth per Conversation

G.711

20 ms

160

50

80 kbps

G.711

30 ms

240

33

74 kbps

G.729A

20 ms

20

50

24 kbps

G.729A

30 ms

30

33

19 kbps

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A more accurate method for provisioning VoIP is to include the Layer 2 overhead, which includes: preambles, headers, flags, CRCs, and ATM cell-padding. The amount of overhead depends on the technology used: •

802.1Q Ethernet adds 32 bytes of Layer 2 overhead.

•

Point-to-point protocol (PPP) adds 12 bytes of Layer 2 overhead.

•

Multilink PPP (MLP) adds 13 bytes of Layer 2 overhead.

•

Frame Relay adds 8 bytes of Layer 2 overhead.

•

ATM adds varying amounts of overhead. depending on the cell-padding requirements.

When Layer 2 overhead is included in the bandwidth calculations, the VoIP call requirements translate to the figures shown in Table 1-2. Table 1-2

Voice Bandw idth (w ith Layer 2 overhead)

Bandw idth Consumption

802.1Q Ethernet

PPP

M LP

Frame-Relay

ATM

G.711 at 50 pps

93 kbps

84 kbps

86 kbps

84 kbps

106 kbps

G.711 at 33 pps

83 kbps

77 kbps

78 kbps

77 kbps

84 kbps

G.729A at 50 pps

37 kbps

28 kbps

30 kbps

28 kbps

43 kbps

G.729A at 33 pps

27 kbps

21 kbps

22 kbps

21 kbps

28 kbps

Bandwidth requirements for voice traffic range from 21 kbps to 106 kbps, depending on the CODEC, the sampling rate, and the Layer 2 media used. Figure 1-2 shows the bandwidth requirements of a G.711 voice call (64 kbps) over Frame-Relay media. Figure 1-2

G.711 Pulse-Code M odulation (PCM ) Voice-Call Over Frame-Relay

84Kbps Single PCM VoIP Call

74635

64Kbps

Voice Control Traffic In centralized call processing designs, the IP phones use a TCP control connection to communicate with the Cisco CallManager. If there is not enough bandwidth provisioned for these lightweight control connections, the user might be adversely affected. For example, let’s look at the Delay to Dial-Tone (DTT) time periods. When an IP phone goes off-hook, it “asks” the CallManager what to do. The CallManager instructs the IP phone to play a Dial-Tone. If control traffic is dropped or delayed within the network, the user will not get the Dial-Tone played out. This same logic applies to all signaling traffic for gateways and phones. For Cisco IP phones, the control traffic required is approximately 150 bps per phone (not including layer 2 overhead).

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Tip

Detailed calculations of call control traffic can be found in the “Network Infrastructure Requirements” chapter of the IP Telephony Solution Reference Network Design Guide.

Quality of Service Requirements for Video When addressing the QoS needs of streaming video traffic, keep the following in mind: •

Loss should be no more than 2%.

•

Latency should be no more than 4-5 seconds (depending on video application's buffering capabilities).

•

There are no significant jitter requirements.

•

Bandwidth requirements depends on the encoding and rate of video stream.

•

Non-entertainment streaming video should be provisioned into the “Silver” data-traffic class. (The silver data class is discussed in “Provisioning for Important Data Traffic” section on page 1-9.)

For video content distribution, keep the following in mind: •

Streaming video content is delay and delay variation insensitive.

•

Streaming video requires large file transfers (traffic patterns similar to FTP sessions).

•

Try to restrict to distribution to less-busy times of day.

•

Provision as “less-than-best-effort” data. (The less-than-best-effort data class is discussed in “Provisioning for Important Data Traffic” section on page 1-9.)

When addressing the QoS needs of video conferencing traffic, keep the following in mind: •

Loss should be no more than 1%.

•

One-way latency should be no more than 150-200 ms.

•

Average jitter should be no more than 30 ms.

•

The minimum bandwidth guarantee is the size of the video conferencing session + 20% (meaning that a 384 kbps video conferencing session requires 460 kbps guaranteed priority bandwidth).

There are two main types of video applications: streaming video (such as IP/TV, which may be either on-demand or multicast) and interactive video (such as video conferencing).

Streaming Video Streaming video applications have more lenient QoS requirements, as they are delay insensitive (the video can take several seconds to 'cue-up'), and are largely delay variation insensitive (due to application buffering). Streaming video may contain valuable content, as in the case of an E-learning application, and therefore may require service guarantees via QoS. Streaming video would be appropriately provisioned in the “Silver” class of data traffic. When you are provisioning for streaming video, you should also take into account the video content distribution requirements. Video file distribution is very similar to FTP traffic in nature and can have a major impact on network performance (due to the file size). Distribution traffic should be managed to avoid impacting the network. For example, video content transfers could be limited to off-peak hours or treated as “less-than-best-effort” traffic.

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Video conferencing Video conferencing has the same loss, delay, and delay variation requirements as voice, but the traffic patterns of video conferencing are radically different from voice. For example, video conferencing traffic has varying packet sizes and extremely variable packet rates (as shown in Figure 1-3.) Figure 1-3

Video conferencing Bandw idth Requirements for a 384 kbps Session

"I" Frame (Full-Sample Video) 1024-1518 Bytes

"I" Frame (Full-Sample Video) 1024-1518 Bytes

600Kbps 30pps "P" and "B" Frames Differential/Predicted Frames 128-256 Bytes 35Kbps

74638

15pps

Because of its bursty nature, video conferencing has two unique requirements in provisioning for strict-priority bandwidth: •

The LLQ must be provisioned to the stream-rate plus 20%.

•

The LLQ burst parameter must be provisioned to 30000 bytes per 384 kbps stream.

Quality of Service Requirements for Data When addressing the QoS needs of data application traffic, keep the following in mind: •

Profile applications to get a basic understanding of their network requirements and traffic patterns.

•

Don't over-engineer the provisioning. Instead, use the proven relative priority model (as explained in the following section).

•

Use no more than four traffic classes, such as: – Gold (Mission-Critical)—Enterprise Resource Planning (ERP), transactional, in-house

software – Silver (Guaranteed-Bandwidth)—Streaming video, messaging, intranet – Bronze (Best-Effort and Default class)—Internet browsing, E-Mail – Less-than-Best-Effort (Optional; higher-drop preferences)—FTP, backups, Peer-to-Peer (P2P)

applications (Napster, KaZaa) •

Do not assign more than 3 applications to each class of protected data traffic.

•

Use proactive provisioning polices before reactive policing policies.

•

Obtain executive endorsement of relative ranking of application priority (from a QoS perspective) prior to committing to the actual policy implementation, to avoid potential derailing of the project.

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Relative Priority vs. Over-Engineering Bandw idth Provisioning Because bandwidth requirements vary greatly from application to application (and even between versions of the same applications) it is not possible to provide a blanket rule for provisioning data bandwidth. Traffic analysis and lab-testing are required to ascertain bandwidth requirements for data applications. Figure 1-4 shows a comparison of traffic patterns between two popular mission-critical ERP applications, Oracle and SAP. Figure 1-4

Oracle versus SAP R/ 3 Packet Distribution

0-64 Bytes

1024-1518 Bytes

65-127 Bytes

512-1023 Bytes

128-252 Bytes

253-511 Bytes

253-511 Bytes 512-1023 Bytes

128-252 Bytes

1024-1518 Bytes

65-127 Bytes 74639

0-64 Bytes Oracle

SAP

In addition to the wide variation of traffic patterns and requirements between different data applications, traffic patterns often vary greatly between two versions of the same application. Figure 1-5 illustrates a situation where the same transaction in one version of SAP requires 35 times more bytes than an earlier version. Figure 1-5

SAP Version Traffic Comparison for Identical Transactions

Bytes per Sales Order Entry (VA01) Transaction 500,000 400,000 300,000 200,000 100,000 SAP GUI, Release 3.0F

SAP GUI, Release 4.6C, with Cache

SAP GUI, Release 4.6C, no Cache

SAP GUI (HTML), Release 4.6C

74640

0

The following is an example of basic bandwidth provisioning for data. An enterprise has as SAP R/3 as its mission-critical application. The task most typically performed by users in the remote offices is the Create Sales Order transaction (VA01). This transaction entails 14 KB of data, which translates to 112 kbps of required bandwidth to ensure a response time of less than 1 second. If SAP is provisioned as a mission-critical application receiving 25% of the link's capacity, then a link size of approximately 512 kbps is required to provide this service-level.

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However, if the enterprise chooses to run a newer version of SAP (4.6c) in an uncompressed HTML format, the VA01 transaction would then require 490 KB per transaction. If link and bandwidth-provisioning remained unchanged, then the new end-user response time would be approximately 32 seconds per transaction. If there is no other traffic traversing the 512 kbps link, the transaction would require approximately 8 seconds. Clearly this is a case where QoS alone is insufficient to accommodate required service-levels given the nature of the data traffic. Continuing the example, let’s assume that the average employee in this enterprise receives 10 MB of e-mail per day (including all attachments). While E-Mail is a highly asynchronous application and is recommended to be classified as best-effort traffic, it nonetheless requires bandwidth. The daily average mail spool divided over an 8 hour workday equates to average of 2.8 kbps of e-mail traffic per employee. If the remote branch has 50 employees, this requirement becomes 140 kbps as a daily average. But, e-mail traffic generally displays a cyclical burst according to time of day (with highest traffic levels between 8-10:30 am). If the assumption is made that e-mail traffic during these periods is double the daily average, then more than 280 kbps of bandwidth could be consumed by e-mail during these hours. These are the type of calculations that should be taken into account not only when provisioning QoS policies, but also in determining when to increase link bandwidth. Absolute application provisioning requires a myriad of assumptions that are unlikely to all hold true on a daily basis. Application updates, fluctuation in the numbers of users, varying business environments, as well as the time of day, month, and year, all affect bandwidth requirements of data applications. Therefore, rather than attempting to determine exact kilobits of bandwidth requirements for data applications, a simpler and proven approach is to assign relative priorities to data applications.

Determining the Classes of Data Traffic It is counterproductive to use too many discrete classes for data traffic. This is because the more classes that are defined, the less the distinction between service-levels. To illustrate, the available bandwidth could be likened to a pie. If the pie is sliced into 64 gradually smaller pieces and then served to respectively important guests (with the largest slice being served to the most important guest), it would be quite difficult to ascertain who's getting the better slivers. Likewise, having too many classes will reduce the overall effectiveness of QoS. Therefore, it is recommended that you define only four classes of data traffic at the most. Additionally, if too many applications are assigned to the highest classes, then the overall effectiveness of QoS provisioning is dampened. Taken to an extreme, if all applications are assigned 'gold' service levels, then the end result is the same as when no QoS is provisioned at all (first-in-first-out scheduling). For this reason, applications provisioned with QoS should be limited to only a select few (maximum 3 applications per class).

Provisioning for Important Data Traffic The relative-priority model suits data applications, as these can easily be categorized into three broad classes of traffic: important, best-effort and less-than-best-effort. Important traffic can additionally be sub-divided into multiple categories, as required. Usually mission-critical traffic is assigned to the highest class of data applications, gold. Mission-critical applications are those that directly contribute to the core operations of an enterprise. These applications are highly-interactive and are therefore sensitive to loss and delay. Examples of mission-critical applications include ERP applications, such as SAP, Oracle, and PeopleSoft, as well as proprietary applications that were designed in-house.

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Some applications are better suited to a silver class of data traffic. Such applications are generally viewed as secondary in importance to business operations or are highly asynchronous in nature. These applications include Netmeeting and messaging applications, calendaring, groupware, and intranet browsing. Best-effort is the default category for data applications. These applications play an indirect role in normal enterprise operations. While some of these applications might be interactive, no bandwidth guarantees are required. Perhaps the best examples of these types of application are E-mail and generic Internet browsing. Less-than-best-effort is a category for applications that are bandwidth intensive and that may not have anything to do with the enterprises' business. These applications are typically highly delay and drop insensitive, and often the executions of such applications span over hours. Therefore, these applications can be given a higher-drop preference to prevent them from robbing bandwidth away from best-effort applications. Examples of less-than-best-effort of traffic include large file transfers, backup operations, and peer-to-peer entertainment-media swapping applications (like Napster, KaZaa, Gnutella).

Reactive vs. Proactive Policies Sometimes administrators chase after the less-than-best-effort traffic and implement limiting policies on these in hopes of indirectly improving available bandwidth to other applications. With this reactive approach, bandwidth is monopolized by unimportant applications until users of important applications complain enough to warrant investigation into the cause by the IT or networking departments. After time, the investigations reveal the culprit application, which is subsequently policed. Performance of the important applications will likely improve, but only until another lesser-important, bandwidth-intensive application emerges. In this approach, the bandwidth-limiting policies will become increasingly complex to administer and will require more CPU overhead to enforce as their complexity grows. A proactive approach is to properly provision (minimum) bandwidth guarantees for important data applications (in their respective orders) and provision a best-effort default class. After these protective policies are in place, optional policing policies can be overlaid for less-than-best-effort traffic. However, the implementation of policing policies creates a static limit that may not always be desirable. For example, data backups, which usually occur overnight, often make use of the additional bandwidth that is available during non-peak hours. With policing policies, the unused bandwidth would not be available, which could cause the backup process to carry over into morning work hours. Therefore, increasing the drop preference of less-than-best- effort traffic (instead of using strict policing policies) is a more efficient use of available bandwidth.

Non-Technical QoS Considerations of Data QoS is essentially segregating applications and giving preference to certain applications over others. With voice and video, the need for QoS is relatively objective and obvious. However, this is not the case with data applications. Arriving at the design principles of relatively few classes of data traffic and also of assigning only a select few applications to these classes opens up a variety of subjective non-technical issues. This is because the enterprise is left to subjectively rank their applications in relative priority. This process is usually very politically and organizationally charged and quite often takes more time to complete than the actual technical portion of a QoS implementation.

Tip

It is important to have agreement (preferably with executive endorsement) on the relative ranking of data applications within the enterprise, otherwise QoS rollout projects could get derailed when disagreements arise over which applications are the more important.

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Service-Provider QoS Requirements End-to-end QoS is like a chain, which is only as strong as the weakest link. Therefore, it's essential for enterprises to use service providers that can provide the service-level agreements required for AVVID applications. For example, the end-to-end requirements of voice and video conferencing are: •

No more than 1% loss

•

No more than 150 ms of one-way latency from mouth-to-ear (per ITU G.114 standard)

•

No more than 30 ms jitter

Thus, the service provider's component (a subset of the trip) must be considerably tighter, as shown below and in Figure 1-6. •

No more than 0.5% loss

•

No more than 60 ms of one-way latency from edge-to-edge

•

No more than 20 ms jitter

Figure 1-6

Service-Provider Service-Level Agreements Required for AVVID

Maximum One-Way Service-Levels Latency < 150 ms / Jitter < 30 ms / Loss < 1%

Enterprise branch office

Enterprise headquarters

Service Provider

IP

IP

74647

Maximum One-Way Service-Provider Service-Levels Latency (enable) set qos acl ip ACL_VOIP_CONTROL dscp 26 tcp any any range 2000 2002

Step 5

Accept incoming Layer 2 CoS classification. cat6k-access> (enable) set port qos 5/1-48 trust trust-cos

Step 6

Inform the port that all QoS associated with the port will be done on a VLAN basis to simplify the configuration. cat6k-access> (enable) set port qos 5/1-48 vlan-based

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Step 7

Instruct the IP phone to rewrite CoS from the PC to CoS of 0 within the IP phone Ethernet ASIC. cat6k-access> (enable) set port qos 5/1-48 trust-ext untrusted

Step 8

Inform the Cisco CallManager port (4/2) that all QoS associated with the port will be done on a port basis cat6k-access> (enable) set port qos 4/2 port-based

Step 9

Write the ACL to hardware. cat6k-access> (enable) commit qos acl all

Step 10

Map the ACL_IP-PHONE ACL to the auxiliary VLAN. cat6k-access> (enable) set qos acl map ACL_IP-PHONES 110

Step 11

Map the ACL_VOIP_CONTROL ACL to the Cisco CallManager port. cat6k-access> (enable) set qos acl map ACL_VOIP_CONTROL 4/2

H.323 Protocol Cisco CallManager communicates with H.323 gateways using TCP ports 1720 (H.225) and 11xxx (H.245). The example below marks H.323 control traffic from Cisco CallManager (4/2) and from H.323 gateways (4/3) with a DSCP of AF31. Step 1

Add entries to the ACL_VOIP_CONTROL access list to mark all traffic from H.323 gateways with a DSCP value of AF31. cat6k-access> (enable) set qos acl ip ACL_VOIP_CONTROL dscp 26 tcp any any eq 1720 cat6k-access> (enable) set qos acl ip ACL_VOIP_CONTROL dscp 26 tcp any any range 11000 11999

Step 2

Inform the Cisco CallManager port (4/2) that all QoS associated with the port will be done on a port basis cat6k-access> (enable) set port qos 4/2 port-based

Step 3

Inform the Cisco H.323 gateway port (4/3) that all QoS associated with the port will be done on a port basis cat6k-access> (enable) set port qos 4/3 port-based

Step 4

Write the ACL to hardware. cat6k-access> (enable) commit qos acl ACL_VOIP_CONTROL

Step 5

Map the ACL_VOIP_CONTROL ACL to the Cisco CallManager port and the H.323 gateway port. cat6k-access> (enable) set qos acl map ACL_VOIP_CONTROL 4/2 cat6k-access> (enable) set qos acl map ACL_VOIP_CONTROL 4/3

M GCP Cisco CallManager communicates with MGCP gateways using User Datagram Protocol (UDP) port 2427. The example below classifies MGCP control traffic from Cisco CallManager (4/2) and from the MGCP gateway (4/4) as DSCP AF31, which is backward compatible with IP Precedence 3.

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Step 1

Add an entry to the ACL_VOIP_CONTROL access list to marking all traffic from MGCP gateways with a DSCP value of AF31. cat6k-access> (enable) set qos acl ip ACL_VOIP_CONTROL dscp 26 udp any any eq 2427

Step 2

Inform the Cisco CallManager port (4/2) that all QoS associated with the port will be done on a port basis cat6k-access> (enable) set port qos 4/2 port-based

Step 3

Inform the Cisco MGCP gateway port (4/4) that all QoS associated with the port will be done on a port basis cat6k-access> (enable) set port qos 4/4 port-based

Step 4

Write the ACL to hardware. cat6k-access> (enable) commit qos acl ACL_VOIP_CONTROL

Step 5

Map the ACL_VOIP_CONTROL ACL to the Cisco CallManager port and the MGCP gateway port. cat6k-access> (enable) set qos acl map ACL_VOIP_CONTROL 4/2 cat6k-access> (enable) set qos acl map ACL_VOIP_CONTROL 4/4

Verifying the ACLs Use the following show command and its associated output for verifying that the ACLs are associated with the correct VLANs and ports. cat6k-access> (enable) sh qos acl map run all ACL name Type Vlans -------------------------------- ---- ------------------------------ACL_IP-PHONES IP 110,111,112 ACL name Type Ports -------------------------------- ---- ------------------------------ACL_IP-PHONES IP ACL name Type Vlans -------------------------------- ---- ------------------------------ACL_VOIP_CONTROL IP ACL name Type Ports -------------------------------- ---- ------------------------------ACL_VOIP_CONTROL IP 4/2,4/3,4/4

M ission-Critical Data As discussed earlier, the classification of any type of traffic as mission-critical could be a controversial move. Take care when classifying mission-critical data. The following configuration example uses a Catalyst 4006 with Supervisor III. In this example, the switch marks IP traffic to and from a specific TCP/IP address with a DSCP of AF21. Step 1

Enable switch-wide QoS. 4006-SUPIII-Access(config)#qos

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To verify, issue the following command (shown with its associated output): 4006-SUPIII-Access#show qos QoS is enabled globally

Step 2

The default CoS-to-DSCP maps must be modified to allow us to trust CoS and maintain DSCP EF and AF31 for VoIP bearer and control traffic respectively. 4006-SUPIII-Access#show qos map cos CoS-DSCP Mapping Table CoS: 0 1 2 3 4 5 6 7 -------------------------------DSCP: 0 8 16 24 32 40 48 56

Change the default CoS-to-DSCP mapping so that CoS 5 equates to EF, CoS 3 equates to AF31, and CoS 4 equates to AF41. 4006-SUPIII-Access(config)#qos map cos 3 to dscp 26 4006-SUPIII-Access(config)#qos map cos 4 to dscp 34 4006-SUPIII-Access(config)#qos map cos 5 to dscp 46

To verify, issue the following command (shown with its associated output): 4006-SUPIII-Access#show qos map cos CoS-DSCP Mapping Table CoS: 0 1 2 3 4 5 6 7 -------------------------------DSCP: 0 8 16 26 34 46 48 56 4006-SUPIII-Access#show qos map dscp tx-queue DSCP-TxQueue Mapping Table (dscp = d1d2) d1 : d2 0 1 2 3 4 5 6 7 8 9 ------------------------------------0 : 01 01 01 01 01 01 01 01 01 01 1 : 01 01 01 01 01 01 02 02 02 02 2 : 02 02 02 02 02 02 02 02 02 02 3 : 02 02 03 03 03 03 03 03 03 03 4 : 03 03 03 03 03 03 03 03 04 04 5 : 04 04 04 04 04 04 04 04 04 04 6 : 04 04 04 04

Step 3

Turn on priority queuing. The default admission to the priority queue is sufficient for our requirements. 4006-SUPIII-Access(config-if-tx-queue)#tx-queue 3 4006-SUPIII-Access(config-if-tx-queue)#priority high

To verify, issue the following command (shown with its associated output): 4006-SUPIII-Access#show qos inter fa 3/4 QoS is enabled globally Port QoS is enabled Port Trust State: 'untrusted' Default DSCP: 0 Default CoS: 0 Tx-Queue Bandwidth ShapeRate Priority (bps) (bps) 1 N/A disabled N/A 2 N/A disabled N/A 3 N/A disabled high 4 N/A disabled N/A

QueueSize (packets) 240 240 240 240

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Selecting an Access-Layer Sw itch

Step 4

Create an ACL to identify the traffic to be marked. 4006-SUPIII-Access(config)#ip access-list extended GOLD-DATA 4006-SUPIII-Access(config-ext-nacl)#remark Match IP Address of the application server 4006-SUPIII-Access(config-ext-nacl)#permit ip any host 192.168.100.1 4006-SUPIII-Access(config-ext-nacl)#permit ip host 192.168.100.1 any

Step 5

Create classes that use the ACL as admission criteria. 4006-SUPIII-Access(config)#class-map match-all GOLD-DATA 4006-SUPIII-Access(config-cmap)#description Mission Critical Traffic 4006-SUPIII-Access(config-cmap)#match access-group name GOLD-DATA

Step 6

Create a service policy that uses the classes for admission criteria and sets the appropriate DSCP label. 4006-SUPIII-Access(config)#policy-map ACCESS-C4006-LAN-EDGE-IN 4006-SUPIII-Access(config-pmap)#description Set DSCP PerHopBehavior Label for Mission Critical Traffic 4006-SUPIII-Access(config-pmap)#class GOLD-DATA 4006-SUPIII-Access(config-pmap-c)#set ip dscp 18

Step 7

Apply the service policy to an interface. 4006-SUPIII-Access#ct Enter configuration commands, one per line. End with CNTL/Z. 4006-SUPIII-Access(config)#int fa 3/4 4006-SUPIII-Access(config-if)#service-policy input ACCESS-C4006-LAN-EDGE-IN

To verify, issue the following command (shown with its associated output): 4006-SUPIII-Access#show pol int fa 3/4 service-policy input: ACCESS-C4006-LAN-EDGE-IN class-map: GOLD-DATA (match-all) 0 packets match: access-group name GOLD-DATA set: ip dscp 18 class-map: class-default (match-any) 0 packets match: any 0 packets

Selecting an Access-Layer Sw itch The Cisco portfolio of Catalyst switches offers a rich selection of access-layer devices. There are many criteria involved when selecting a device for this layer of your network. When AVVID solutions are involved, there is a base set of features required to support IP telephony, which is a major component of the AVVID solution. •

The switch must support multiple VLANs on the access port to which the IP phone is attached. This is currently supported via the voice VLAN command for IOS-based switches and the auxiliary VLAN command for Catalyst OS-based switches.

•

The switch must be able to manipulate the IP phones trust boundary and marking capabilities. This functionality is supported via the switchport priority command in IOS-based switches and the trust-ext command in Catalyst OS-based switches.

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•

The switch must be able trust the CoS or DSCP marking that the IP phones provide. This is currently supported via the mls QoS trust CoS and mls QoS trust DSCP commands for IOS-based switches and the trust-CoS and trust-DSCP commands for Catalyst OS-based switches.

As mentioned before (in the “Server Farm Switch Selection” section on page 3-6), there are times when the devices attached to an AVVID network do not classify their traffic with the appropriate Layer 2 and Layer 3 markings. When considering your choices for access-layer devices, consider the switch’s ability to classify and mark traffic at the edge of the network via ACLs and service policies. This will allow QoS to be offered as a service throughout the network and administered at the edge of the network where CPU resources are plentiful, rather than at the distribution and core aggregation points where enforcement of QoS classification and marking could adversely affect network performance.

Catalyst 6500 as an Access-Layer Sw itch One of the most popular campus configurations for Cisco AVVID solutions is to use Catalyst 6500 switches in both the wiring closet and the distribution and core layers. There are several compelling reasons for this: •

The Catalyst 6500 supports dual supervisor engines providing the highest availability of access solutions.

•

The Catalyst 6500 can provide in-line power to the IP phones. The current 10/100 boards for the Catalyst 6500 support integrated inline power and are standard.

•

The Catalyst 6500 offers the highest growth potential.

•

The Catalyst 6500 supports advanced Layer 2/3 campus QoS tools.

Figure 3-6 shows a general model for the Catalyst 6500 as an access device (as illustrated in the QoS configurations discussed in this chapter).

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Figure 3-6

General M odel for Catalyst 6500 QoS Configurations

Core

Si

Distribution

Si

Si

Catalyst 6500

Catalyst 6500 w/ PFC

Access VVID=110

VLAN=10

74697

IP

With the addition of the PFC, the Catalyst 6500 is capable of handling Layer 2, 3, and 4 QoS tasks. The PFC can be used to enable advanced QoS tools, such as packet classification and marking, scheduling, and congestion avoidance, based on either Layer 2 or Layer 3 and 4 header information. You can configure multiple receive and transmit queues with thresholds that can be used according to the QoS policy rules configured in the switch. There are also many versions of Catalyst 6500 line cards with varying QoS capabilities. (See Appendix A, “Reference Information” for a list of linecards and queuing mechanisms available for the Catalyst 6500.) The newest cards include enhanced QoS features that provide priority queuing capabilities for both ingress and egress interfaces. With the exception of the priority queue, which is always serviced as soon as frames are present, the queues are serviced in the WRR method. Each queue is given a user-configurable weight. By default, the “high” queue is given 98% of the scheduler time and the “low” queue is given 2%. This ratio is conducive to ensuring that packets with a low delay-tolerance are not delayed in a queue. This is also the reason behind giving the “low” queue a much higher percentage of the overall interface buffer.

Note

Because the Catalyst OS is designed for switches that operate in the “closet” and Native IOS is designed for switches that operate at the distribution layer of the network, a Catalyst 6500 that is functioning as an access-switch should be equipped with Catalyst OS. To see how a port is configured, issue the show port capabilities mod/port Catalyst OS command. The default QoS capabilities of the port can be changed using the set qos map and set qos wred-threshold commands. When modifying the queue thresholds, it is important to remember that the higher priority queue has a higher numerical value.

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After you have connected the IP phone to the access-layer switch, it is time to configure the QoS parameters on the switch. This includes setting up multiple queues on all ports, configuring access to the queues, setting thresholds for congestions avoidance, and connecting the switch to the distribution or core layer. For the Catalyst 6500, QoS requires the following changes to the configuration of the access switch: 1. Enable switch-wide QoS. 2. Configure the IP phone port queuing. 3. Configure the uplink interface to the distribution switch, including enabling trust for Ethernet

frames coming into the trunk port, manipulating the CoS-to-queue mapping entrance criteria, and mapping the CoS and IP Precedence values to the appropriate DSCP value.

Enabling QoS To enable QoS on the access-layer Catalyst 6500, do the following: Step 1

Enable switch-wide QoS. cat6k-access> (enable) set qos enable

Configuring IP Phone Port Queuing If you use a single cable to connect an IP phone, the access port is configured to trust the IP phone and not the attached PC. The port is also configured to use multiple transmit queues, one being a priority queue for voice traffic. Figure 3-7

Connecting an IP phone to a Catalyst 6500

Auxilary VLAN = 110

PC VLAN = 10

Catalyst 6500 w/ PFC

IP Phone = IP Subnet 110

Desktop PC: IP Subnet 10

74698

IP

To configure IP phone port queuing, do the following: Step 1

Inform the port that all QoS associated with the port will be done on a VLAN basis. cat6k-access> (enable) set port qos 5/1-48 vlan-based

Step 2

Instruct the IP phone to rewrite CoS from the PC to CoS of 0 within the IP phone Ethernet ASIC. cat6k-access> (enable) set port qos 5/1-48 trust-ext untrusted

Step 3

Accept incoming Layer 2 CoS classification. (Current 10/100 version “1” linecards must still have trust-cos enabled even though the parser returns an error.) cat6k-access> (enable) set port qos 5/1-48 trust trust-cos

Step 4

Create an access list that accepts incoming Layer 3 ToS classification (necessary only on 10/100 ports). cat6k-access> (enable) set qos acl ip ACL_IP-PHONES trust-cos any

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Step 5

Write the ACL to hardware. cat6k-access> (enable) commit qos acl ACL_IP-PHONES

Step 6

Map the access list to the Auxiliary VLAN. cat6k-access> (enable) set qos acl map ACL_IP-PHONES 110

Once QoS has been enabled on the Catalyst 6500 access-layer switch, you can use the following command to place all traffic with a CoS of 3 (VoIP control) into the second transmit queue (with a low drop threshold), to ensure successful call control during periods of heavy congestion. All traffic with a CoS of 5 (VoIP RTP Bearer) is placed into the second queue by default. cat6k-access> (enable) set qos map 2q2t tx 2 1 cos 3

Configuring the Uplink to the Distribution Sw itch Once you have configured the access port queuing, you must also configure the uplink interfaces to the distribution, or core, switch. This involves enabling trust for Ethernet frames coming into the trunk port (1/1 in this example), manipulating the CoS-to-queue mapping entrance criteria, and mapping the CoS and IP Precedence values to the appropriate DSCP value.

Configuring Transmit Queues All VoIP (CoS of 5) traffic will be placed into the egress interface priority queue on 1p2q2t interfaces and queue 2 on 2q2t interfaces as soon as you enable QoS. However, you must perform the additional step of configuring the Catalyst 6500 CoS queue admission rules to ensure that traffic with a CoS of 3 (VoIP control) is placed into the second queue. Step 1

Place CoS of 3 in queue 2 for 1p2q2t. cat6k-access> (enable) set qos map 1p2q2t tx 2 1 cos 3

Step 2

Place CoS of 3 in queue 2 for 2q2t. cat6k-access> (enable) set qos map 2q2t tx 2 1 cos 3

M odifying CoS-to DSCP and IP Precedence-to-DSCP M appings Cisco follows the IETF recommendations for setting the DSCP classification values for both the VoIP control plane traffic and VoIP bearer or media plane traffic. The recommended settings are DSCP of AF31 for VoIP control plane and DSCP of EF for VoIP bearer plane. To map the Layer 2 CoS and Layer 3 IP Precedence settings correctly to these DSCP values, you must modify the default CoS/IP Precedence-to-DSCP mappings. Step 1

Modify the CoS-to-DSCP mappings. cat6k-access> (enable) set qos cos-dscp-map 0 8 16 26 34 46 48 56

Step 2

Modify the IP Precedence-to-DSCP mappings. cat6k-access> (enable) set qos ipprec-dscp-map 0 8 16 26 34 46 48 56

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Verifying the Configuration One of the fundamental processes of implementing QoS is verifying that the configurations are correct and are performing as expected. On the Catalyst 6500 access-layer switch, you can verify the configuration and performance during periods of high congestion by examining the output of the following commands: Command

Description

See

show port qos mod/port

Displays the QoS settings for the specified port.

Example 3-1

show qos info runtime mod/port

Displays QoS runtime information for the specified port.

Example 3-2

show mac mod/port

Displays Media Access Control TX ringMAC) Example 3-3 information for the specified port.

show qos statistics l3

Displays summary QoS statistics for all ports. Example 3-4

show qos stat mod/port

Displays detailed QoS statistics for the specified port.

Example 3-5

show qos map run cos-dscp-map

Displays the CoS-to-DSCP mappings.

Example 3-6

show qos map run ipprec-dscp-map

Displays the IP Precedence-to-DSCP mappings.

Example 3-7

Example 3-1

Displaying QoS Settings for a Port

cat6k-access> (enable) show port qos 5/1 QoS is enabled for the switch QoS policy source for the switch set to local. Port

Interface Type Interface Type Policy Source Policy Source config runtime config runtime ----- -------------- -------------- ------------- ------------5/1 vlan-based vlan-based COPS local Port

TxPort Type

RxPort Type

Trust Type Trust Type Def CoS Def CoS config runtime config runtime ----- ------------ ------------ ------------ ------------- ------- ------5/1 2q2t 1q4t trust-cos trust-cos* 0 0 Port Ext-Trust Ext-Cos ----- --------- ------5/1 untrusted 0 (*)Runtime trust type set to untrusted. Config: Port ACL name Type ----- -------------------------------- ---No ACL is mapped to port 5/1. ACL is mapped to VLAN Runtime: Port ACL name Type ----- -------------------------------- ---No ACL is mapped to port 5/1.

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Example 3-2

Displaying QoS Runtime Information

cat6k-access>(enable) show qos info run 5/1 Run time setting of QoS: QoS is enabled Policy Source of port 5/1: Local Current 10/100 "1" linecards support 2q2t/1q4t only Tx port type of port 5/1 : 2q2t Rx port type of port 5/1 : 1q4t Interface type: vlan-based ACL is mapped to VLAN ACL attached: The qos trust type is set to trust-cos. Warning: Runtime trust type set to untrusted. Default CoS = 0 Queue and Threshold Mapping for 2q2t (tx): Queue Threshold CoS ----- --------- --------------1 1 0 1 1 2 2 2 1 3 4 5 2 2 6 7 Queue and Threshold Mapping for 1q4t (rx): Queue Threshold CoS ----- --------- --------------1 1 0 1 1 2 2 1 3 3 4 5 1 4 6 7

Example 3-3

Displaying M AC Information

cat6k-access> (enable) show mac 5/1 Port Rcv-Unicast Rcv-Multicast Rcv-Broadcast -------- -------------------- -------------------- -------------------5/1 267223 37 4 Port Xmit-Unicast Xmit-Multicast Xmit-Broadcast -------- -------------------- -------------------- -------------------5/1 28748894 5206 72 Port Rcv-Octet Xmit-Octet -------- -------------------- -------------------5/1 17178128 1840430081 "Out-Discards" are packets drooped due to congestion in the tx interface buffers MAC Dely-Exced MTU-Exced In-Discard Out-Discard -------- ---------- ---------- ---------- ----------5/1 0 0 0 262140

Example 3-4

Displaying QoS Summary Statistics

cat6k-access> (enable) show qos stat l3 VoIP Control packets that have been re-written with CoS=3/DSCP=26 (AF31) Packets dropped due to policing: 0 IP packets with ToS changed: 1885 IP packets with CoS changed: 781 Non-IP packets with CoS changed: 0

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Example 3-5

Displaying QoS Detailed Statistics

cat6k-access> (enable) show qos stat 5/1 All packets dropped are in the 1st drop threshold of queue #1 Tx port type of port 5/1 : 2q2t Q # Threshold #:Packets dropped --- ----------------------------------------------1 1:393210 pkts, 2:0 pkts 2 1:0 pkts, 2:0 pkts Rx port type of port 5/1 : 1q4t Q # Threshold #:Packets dropped --- ----------------------------------------------1 1:0 pkts, 2:0 pkts, 3:0 pkts, 4:0 pkts

Example 3-6

Displaying CoS-to-DSCP M appings

cat6k-access> (enable) show qos map run cos-dscp-map CoS - DSCP map: CoS DSCP -----0 0 1 8 2 16 3 26 26 = AF31 Voice Control 4 34 34 = AF41 IP Video Conferencing 5 46 46 = EF Voice Bearer 6 48 7 56

Example 3-7

Displaying IP Precedence-to-DSCP M appings

cat6k-access> (enable) show qos map run ipprec-dscp-map IP-Precedence - DSCP map: IP-Prec DSCP ---------0 0 1 8 2 16 3 26 26 = AF31 Voice Control 4 34 34 = AF41 IP Video Conferencing 5 46 46 = EF Voice Bearer 6 48 7 56

Catalyst 4000 as an Access-Layer Sw itch Another popular campus configuration for Cisco AVVID networks uses the Catalyst 2948G, the Catalyst 2980G, and the Catalyst 4000 family of switches in the wiring closets. There are several compelling reasons for this, including: •

The Catalyst 4006 can provide in-line power to the IP phones.

•

The Catalyst 4000 offers a very low price per port.

•

These switches provide extremely scalable, high-speed switching.

Starting with Catalyst OS Release 5.2, the Catalyst 4000 switches support dual-transmit queues on every interface. Admission to the queues is based on Layer 2 CoS markings and is configurable in 802.1p user priority pairs.

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Note

From a configuration perspective, the Catalyst 2948G, the Catalyst 2980G, and the Catalyst 4000 family of switches are the same. Therefore, the configuration of only one, the Catalyst 4000, is shown in this section.

Catalyst 4000 w ith Supervisor III The Catalyst 4000 Supervisor III introduces many enhanced QoS features to the Catalyst 4000, including four queues per port with a configurable priority queue. Figure 3-8 shows a general model for the Catalyst 4000 with Supervisor III as an access device (as illustrated in the QoS configurations discussed in this chapter). Figure 3-8

General M odel for Catalyst 4000 w ith Supervisor III QoS Configurations

Core

Si

Distribution

Si

Si

Catalyst 6500

Catalyst 4000

Access VVID=111

VLAN=11

74699

IP

This section presents suggested configurations for port scheduling and queuing on the Catalyst 4000 with Supervisor III. In general: •

The recommended configuration for the receive interface is FIFO—one standard FIFO queue.

•

The recommended configuration for the transmit interface is 1P3Q1T—one priority queue (when configured) and three queues with a single threshold. Scheduling is done on a WRR basis. Admission to the queues is based on IP DSCP value and is user configurable.

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For the Catalyst 4000 with Supervisor III, QoS requires the following changes to the configuration of the access switch: 1. Enable QoS globally. 2. Modify the default CoS-to-DSCP mapping so that CoS 3 = AF31, CoS 4 = AF41, and CoS 5 = EF. 3. Enable priority queuing (per port). The default admission criteria for the priority queue matches our

requirements. 4. Configure an ACL to identify traffic to be marked, associate it with a service policy, and apply the

service policy to the interface. 5. Configure a port to support an IP phone. 6. Configure uplink scheduling and trust (CoS or DSCP).

Enabling QoS To enable QoS on the access-layer Catalyst 4000 with Supervisor III, do the following: Step 1

Enable switch-wide QoS. 4006-SUPIII-Access(config)#qos

M odifying the CoS-to-DSCP M appings There are 8 CoS labels and 64 possible DSCP labels. To trust the CoS markings, the default CoS-to-DSCP mapping table must be modified to equate CoS 3 (VoIP control traffic) to AF31, CoS 5 (VoIP bearer traffic) to EF, and CoS 4 (video conferencing) to AF41. Step 1

The default CoS-to-DSCP mappings are as follows: 4006-SUPIII-Access#show qos map cos CoS-DSCP Mapping Table CoS: 0 1 2 3 4 5 6 7 -------------------------------DSCP: 0 8 16 24 32 40 48 56

Change the default mapping table so that CoS 3 = AF31, CoS 4 = AF41, and CoS 5 = EF. Remember to use the decimal equivalents. 4006-SUPIII-Access(config)#qos map cos 3 to dscp 26 4006-SUPIII-Access(config)#qos map cos 4 to dscp 34 4006-SUPIII-Access(config)#qos map cos 5 to dscp 46

Enabling Priority Queuing To enable priority queuing, do the following:

Note

In the Catalyst 4000 with Supervisor III, only queue number 3 can be enabled for priority queuing.

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Step 1

Specify the transmit queue. 4006-SUPIII-Access(config-if-tx-queue)#tx-queue 3

Step 2

Set the priority to high. 4006-SUPIII-Access(config-if-tx-queue)#priority high

Configuring ACLs There are times when classification of traffic by the access-layer switch is required. The Catalyst 4000 with Supervisor III has a powerful set of features that allow traffic to be classified as it enters the network. To classify VoIP bearer and control traffic as it enters the network, do the following: Step 1

Create an ACL to match the traffic to be prioritized. 4006-SUPIII-Access(config)#ip access-list extended GOLD-DATA 4006-SUPIII-Access(config-ext-nacl)#remark Match IP Address of the application server 4006-SUPIII-Access(config-ext-nacl)#permit ip any host 192.168.100.1 4006-SUPIII-Access(config-ext-nacl)#permit ip host 192.168.100.1 any 4006-SUPIII-Access(config)#ip access-list extended VOICE 4006-SUPIII-Access(config-ext-nacl)#remark Match the UDP ports that VoIP Uses for Bearer Traffic 4006-SUPIII-Access(config-ext-nacl)#permit udp any any range 16384 32767 4006-SUPIII-Access(config)#ip access-list extended VOICE-CONTROL 4006-SUPIII-Access(config-ext-nacl)#remark Match VoIP Control Traffic 4006-SUPIII-Access(config-ext-nacl)#remark SCCP 4006-SUPIII-Access(config-ext-nacl)#permit tcp any any range 2000 2002 4006-SUPIII-Access(config-ext-nacl)#remark H323 Fast Start 4006-SUPIII-Access(config-ext-nacl)#permit tcp any any eq 1720 4006-SUPIII-Access(config-ext-nacl)#remark H323 Slow Start 4006-SUPIII-Access(config-ext-nacl)#permit tcp any any range 11000 11999 4006-SUPIII-Access(config-ext-nacl)#remark H323 MGCP 4006-SUPIII-Access(config-ext-nacl)#permit udp any any eq 2427

Step 2

Create classes based on the ACL. 4006-SUPIII-Access(config)#class-map match-all GOLD-DATA 4006-SUPIII-Access(config-cmap)#description Mission Critical Traffic 4006-SUPIII-Access(config-cmap)#match access-group name GOLD-DATA 4006-SUPIII-Access(config)#class-map match-all VOICE 4006-SUPIII-Access(config-cmap)#description VoIP Bearer Traffic 4006-SUPIII-Access(config-cmap)#match access-group name VOICE 4006-SUPIII-Access(config)#class-map match-all VOICE-CONTROL 4006-SUPIII-Access(config-cmap)#description VoIP Control Traffic (SCCP, H225, H254, MGCP) 4006-SUPIII-Access(config-cmap)#match access-group name VOICE-CONTROL

Step 3

Create a policy to set the DSCP PHB label for the classes. 4006-SUPIII-Access(config)#policy-map ACCESS-C4006-LAN-EDGE-IN 4006-SUPIII-Access(config-pmap)#description Set DSCP PerHopBehavior Label for VOIP Control and Bearer Traffic 4006-SUPIII-Access(config-pmap)#class VOICE-CONTROL 4006-SUPIII-Access(config-pmap-c)#set ip dscp 26 4006-SUPIII-Access(config-pmap)#class VOICE 4006-SUPIII-Access(config-pmap-c)#set ip dscp 46 4006-SUPIII-Access(config-pmap)#class GOLD-DATA 4006-SUPIII-Access(config-pmap-c)#set ip dscp 18

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Step 4

Apply the policy to a physical interface. 4006-SUPIII-Access(config)#int fa 4/1 4006-SUPIII-Access(config-if)#service-policy input ACCESS-C4006-LAN-EDGE-IN

Configuring Access-Layer Phone Support When the Catalyst 4000 with Supervisor III is connected to an IP phone, do the following: Step 1

Configure the switch to trust CoS from the IP Phone. 4006-SUPIII-Access(config)#int fa 4/5 4006-SUPIII-Access(config-if)#qos trust cos

Step 2

Enable the voice and data VLANs. 4006-SUPIII-Access(config-if)#switchport voice vlan 111 4006-SUPIII-Access(config-if)#switchport access vlan 11

Step 3

Set the IP Phones trust boundary. 4006-SUPIII-Access(config-if)#switchport priority extend cos 0

Step 4

While in interface configuration mode, enable priority queueing on the port.

Note

In the Catalyst 4000 with Supervisor III, only queue number 3 can be enabled for priority queuing.

4006-SUPI(config-if-tx-queue)#tx-queue 3 4006-SUPI(config-if-tx-queue)#priority high

Configuring the Uplink to the Distribution Sw itch The ports attached to the distribution layer require a slightly different configuration. These ports must be configured to trust DSCP or CoS depending on the capabilities of the distribution-layer switch attached. In the following configuration, port 3/1 is attached to a Layer 3-aware distribution device and can trust DSCP arriving from it. Port 3/2 illustrates an example where CoS-only classification is used.

Note

Step 1

The system-wide CoS-to-DSCP mapping and DSCP-to-queue admission criteria configurations must have been completed and the priority queue must be enabled for these ports in order for the access-layer uplink ports to perform QoS as expected.

Configure DSCP trust. 4006-SUPIII-Access(config)#int g 3/1 4006-SUPIII-Access(config-if)#qos trust dscp

Step 2

Enable the priority queue on this interface. 4006-SUPI(config-if-tx-queue)#tx-queue 3 4006-SUPI(config-if-tx-queue)#priority high

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Step 3

Configure CoS trust. 4006-SUPIII-Access(config-if)#int g 3/2 4006-SUPIII-Access(config-if)#qos trust cos

Step 4

Enable the priority queue on this interface. 4006-SUPI(config-if-tx-queue)#tx-queue 3 4006-SUPI(config-if-tx-queue)#priority high

Verifying the Configuration On the Catalyst 4000 access-layer switch, you can verify the configuration and performance during periods of high congestion by examining the output of the following commands: Command

Description

See

show qos map cos

Displays the QoS CoS mapping information.

Example 3-8

show qos map dscp

Displays the QoS DSCP mapping information. Example 3-9

show qos interface interface

Displays QoS queuing information.

Example 3-10

show policy-map interface

Displays statistics and configurations of input and output policies attached to an interface.

Example 3-11

show interface counters

Displays statistics regarding traffic seen on the Example 3-12 physical interface.

Example 3-8

Displaying QoS CoS M apping Information

4006-SUPIII-Access#show qos map cos CoS-DSCP Mapping Table CoS: 0 1 2 3 4 5 6 7 -------------------------------DSCP: 0 8 16 26 34 46 48 56

Example 3-9

Displaying QoS DSCP M apping Information

4006-SUPIII-Access#show qos map dscp tx-queue DSCP-TxQueue Mapping Table (dscp = d1d2) d1 : d2 0 1 2 3 4 5 6 7 8 9 ------------------------------------0 : 01 01 01 01 01 01 01 01 01 01 1 : 01 01 01 01 01 01 02 02 02 02 2 : 02 02 02 02 02 02 02 02 02 02 3 : 02 02 03 03 03 03 03 03 03 03 4 : 03 03 03 03 03 03 03 03 04 04 5 : 04 04 04 04 04 04 04 04 04 04 6 : 04 04 04 04

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Example 3-10 Displaying QoS Queuing Information 4006-SUPIII-Access#show qos interface fa 4/1 QoS is enabled globally Port QoS is enabled Port Trust State: 'untrusted' Default DSCP: 0 Default CoS: 0 Tx-Queue Bandwidth ShapeRate Priority (bps) (bps) 1 N/A disabled N/A 2 N/A disabled N/A 3 N/A disabled high 4 N/A disabled N/A

QueueSize (packets) 240 240 240 240

4006-SUPIII-Access#show qos int g 3/1 QoS is enabled globally Port QoS is enabled Port Trust State: 'dscp' Default DSCP: 0 Default CoS: 0 Tx-Queue Bandwidth ShapeRate Priority (bps) (bps) 1 250000000 disabled N/A 2 250000000 disabled N/A 3 250000000 disabled high 4 250000000 disabled N/A

QueueSize (packets) 1920 1920 1920 1920

4006-SUPIII-Access#show qos int g 3/2 QoS is enabled globally Port QoS is enabled Port Trust State: 'cos' Default DSCP: 0 Default CoS: 0 Tx-Queue Bandwidth ShapeRate Priority (bps) (bps) 1 250000000 disabled N/A 2 250000000 disabled N/A 3 250000000 disabled high 4 250000000 disabled N/A

QueueSize (packets) 1920 1920 1920 1920

Example 3-11 Displaying Policy Information 4006-SUPIII-Access#show policy-map interface fa 4/1 service-policy input: ACCESS-C4006-LAN-EDGE-IN class-map: GOLD-DATA (match-all) 0 packets match: access-group name GOLD-DATA set: ip dscp 18 class-map: VOICE-CONTROL (match-all) 0 packets match: access-group name VOICE-CONTROL set: ip dscp 26 class-map: VOICE (match-all) 0 packets match: access-group name VOICE set: ip dscp 46

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class-map: class-default (match-any) 0 packets match: any 0 packets

Example 3-12 Displaying Traffic Statistics 4006-SUPIII-Access#show int g3/2

count all

Port Gi3/2

InBytes 0

InUcastPkts 0

InMcastPkts 0

InBcastPkts 0

Port Gi3/2

OutBytes 0

OutUcastPkts 0

OutMcastPkts 0

OutBcastPkts 0

Port Gi3/2

InPkts 64 0

OutPkts 64 0

InPkts 65-127 0

OutPkts 65-127 0

Port Gi3/2

InPkts 128-255 0

OutPkts 128-255 0

InPkts 256-511 0

OutPkts 256-511 0

Port Gi3/2

InPkts 512-1023 0

OutPkts 512-1023 0

Port Gi3/2

InPkts 1024-1518 OutPkts 1024-1518 InPkts 1519-1548 OutPkts 1519-1548 0 0 0 0

Port Gi3/2

InPkts 1024-1522 OutPkts 1024-1522 InPkts 1523-1548 OutPkts 1523-1548 N/A N/A N/A N/A

Port

InPkts 1549-9216 OutPkts 1549-9216

Port Gi3/2

InPkts 1549-9216 OutPkts 1549-9216 0 0

Port Gi3/2

Tx-Bytes-Queue-1 0

Tx-Bytes-Queue-2 Tx-Bytes-Queue-3 0 0

Tx-Bytes-Queue-4 0

Port Gi3/2

Tx-Drops-Queue-1 0

Tx-Drops-Queue-2 Tx-Drops-Queue-3 0 0

Tx-Drops-Queue-4 0

Port Gi3/2

Rx-No-Pkt-Buff 0

Port Gi3/2

UnsupOpcodePause 0

Port Gi3/2

RxPauseFrames 0

TxPauseFrames 0

PauseFramesDrop 0

CrcAlign-Err 0

TxCrc-Err 0

Collisions 0

Symbol-Err 0

Port Gi3/2

Undersize 0

Oversize 0

Fragments 0

Jabbers 0

Port Gi3/2

Single-Col 0

Multi-Col 0

Late-Col 0

Excess-Col 0

Port Gi3/2

Deferred-Col 0

False-Car 0

Carri-Sen 0

Sequence-Err 0

Port Gi3/2

RxIslTagFrames 0

TxIslTagFrames RxDot1qTagFrames 0 0

TxDot1qTagFrames 0

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Port Gi3/2

RxMacFifoOverrun RxMacFifoUnderrun RxCdmFifoOverrun TxCsmFifoUnderrun 0 0 0 0

Port Gi3/2

NoPBA/CdmFifoOverun 0

Catalyst 4000 w ith Supervisor II Figure 3-9 shows a general model for the Catalyst 4000 with Supervisor II as an access device (as illustrated in the QoS configurations discussed in this chapter). Figure 3-9

General M odel for Catalyst 4000 w ith Supervisor II QoS Configurations

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Catalyst 4000

Access VVID=111

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This section presents suggested configurations for port scheduling and queuing on the Catalyst 4000 with Supervisor II. In general: •

The recommended configuration for the receive interface is 1Q-FIFO—one standard FIFO queue.

•

The recommended configuration for the transmit interface is 2Q1T—two standard queues with a single threshold. Scheduling is on a round-robin basis. Admission to the queues is based on 802.1p CoS value and is user configurable in pairs. If you enable QoS but do not modify the CoS-to-transmit queue mappings, switch performance could be affected because all traffic is assigned to queue 1. Once QoS is enabled on the Catalyst 4000, you must change the CoS mappings to use the newly created queue.

•

The default queue admission criteria for the Catalyst 4000 is: CoS 0 through 7 goes to queue 1, all other (broadcast, multicast, and unknown) traffic goes to queue 2.

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For the Catalyst 4000 with Supervisor II, QoS requires the following changes to the configuration of the access switch: 1. Enable QoS globally. 2. Verify the queue admission configuration. 3. Configure the IP phone port queuing. 4. Configure the uplink to the distribution switch.

Enabling QoS By default, only one queue is enabled on the Catalyst 4000 line of switches. To enable the second queue, use the set qos map command. VoIP Control (CoS of 3) frames should be placed into the second queue. These maps must be configured in pairs of CoS values because the Catalyst 4000 examines only the first two CoS bits. To enable QoS and establish the second queue, do the following. Step 1

Enable QoS. cat4k> (enable) set qos enable

Step 2

Map the CoS categories to the queues. cat4k> cat4k> cat4k> cat4k>

(enable) (enable) (enable) (enable)

set set set set

qos qos qos qos

map map map map

2q1t 2q1t 2q1t 2q1t

1 2 2 2

1 1 1 1

cos cos cos cos

0-1 2-3 4-5 6-7

Verifying Queue Admission Configuration To verify the queue admission configuration on the Catalyst 4000, use the following command (shown with its associated output): cat4k> (enable) show qos info runtime Run time setting of QoS: QoS is enabled All ports have 2 transmit queues with 1 drop thresholds (2q1t). Default CoS = 0 Queue and Threshold Mapping: Queue Threshold CoS ----- --------- --------------1 1 0 1 2 1 2 3 4 5 6 7

Configuring IP Phone Port Queuing In the Catalyst OS Release 5.5.1, the Catalyst 4000 line does not offer any advanced IP phone queuing features. Because of this, the Catalyst 4000 depends on the default CoS marking and enforcement on the IP phone.

Configuring the Uplink Interface to the Distribution Sw itch Queuing is automatically enabled when QoS is been enabled and classification and queue admission have been configured. Therefore, no special queuing or scheduling commands need to be configured on the Catalyst 4000 side of the link (from the access-layer Catalyst 4000 to the distribution-layer Catalyst 6500).

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If you are using the Catalyst 4000 with the Layer 3 engine (the WS-X4232), which enables IP, IPX, and Multicast routing for the switch, you can perform additional uplink configuration. The Layer 3 engine allows the Catalyst 4000 to support four standard transmit queues with a single threshold on the two-gigabit uplinks. The four queues are scheduled using a user-configurable WRR algorithm. Admission to the queues is based on 802.1p CoS value and is user-configurable in pairs. To enable QoS and change CoS mappings to use the newly created queues, do the following: Step 1

Enable QoS cat4k> (enable) set qos enable

Step 2

Map the CoS categories to each of the queues. cat4k> cat4k> cat4k> cat4k>

(enable) (enable) (enable) (enable)

set set set set

qos qos qos qos

map map map map

4q1t 4q1t 4q1t 4q1t

1 2 3 4

1 1 1 1

cos cos cos cos

6-7 4-5 2-3 0-1

Note that the Layer 3 queue numbering is the reverse of the Layer 2 numbering.

Catalyst 3524-PW R XL as an Access-Layer Sw itch Figure 3-10 shows a general model for the Catalyst 3524-PWR XL as an access device (as illustrated in the QoS configurations discussed in this chapter). Figure 3-10 General M odel for Catalyst 3524-PWR XL QoS Configurations

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Catalyst 3524-PWR

Access VVID=112

VLAN=12

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This section presents suggested configurations for port scheduling and queuing on the Catalyst 3524-PWR XL. In general: •

The recommended configuration for the receive interface is 1Q-FIFO—one standard FIFO queue.

•

The recommended configuration for the 10/100 transmit interface is 2Q1T—two standard queues with a single threshold. Scheduling is done on a priority-scheduling basis. Admission to the queues is based on 802.1p CoS or port priority CoS value and is not user configurable. The queue admission criteria for the Catalyst 3500 are as follows: queue1: CoS 0 through 3, queue 2: CoS 4 through 7.

•

The recommended configuration for the gigabit Ethernet transmit interface is 8Q-FIFO—eight standard queues with a single drop threshold. Currently, only two queues are used. Scheduling is done on a priority-scheduling basis. Admission to the queues is based on 802.1p or port priority CoS values and is not user configurable. The gigabit Ethernet queue admission criteria are as follows: queue 1: CoS 0 through 3, queue 2: CoS 4 through 7, queues 3-8: not used.

For the Catalyst 3524-PWR XL, QoS requires the following changes to the configuration of the access switch: 1. Configure the IP phone port queuing. 2. Configure the uplink to the distribution switch.

Configuring IP Phone Port Queuing If you use a single cable to install an IP phone, the access port is configured to trust the IP phone and not the attached PC. The port is also configured to use multiple transmit queues on all interfaces. To configure IP phone port queuing, do the following: Step 1

Enter interface configuration mode: c35k(config)#interface FastEthernet0/1

Step 2

Set the encapsulation format on the trunk port to 802.1Q. With this format, the switch supports simultaneous tagged and untagged traffic on a port. c35k(config-if)#switchport trunk encapsulation dot1q

Step 3

Set the native VLAN for sending and receiving untagged traffic when the interface is in 802.1Q trunking mode. Valid IDs are from 1 to 4094. Do not enter leading zeros. c35k(config-if)#switchport trunk native vlan 12

Step 4

Configure the port as a trunk port. c35k(config-if)#switchport mode trunk

Step 5

Configure the VLAN to be used for voice. c35k(config-if)#switchport voice vlan 112

Step 6

Set the IP phone port to override the priority received from PC or the attached device. c35k(config-if)#switchport priority extend cos 0

Step 7

Enable the Port Fast feature on an interface in all its associated VLANs. c35k(config-if)#spanning-tree portfast

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Configuring the Uplink Interface to the Distribution Sw itch The recommended design for wiring closet configurations of Catalyst 3500 XL family of Catalyst switches is a star topology. A Catalyst 3500 family GigaStack configuration cannot provide guaranteed voice QoS because it is essentially a shared media access model. The basic concern is the behavior of the GigStack GBIC when you use both ports of the GBIC. GigaStack is a half-duplex connection. Because it is half duplex, you cannot guarantee voice quality if you use both ports of the GigaStack GBIC. So where you use stacked switches, you need to use only one port in the GigaStack GBIC. This will mean that you use more GigaStack GBICS. However, this design will avoid any half- duplex, non-deterministic behavior. Additionally, when you create stacks of switches you need to keep in mind how your traffic will flow and how many devices will be participating in a Layer 2 convergence event. In general, if you have to stack, design small stacks so that you will be able to tune spanning tree for fast convergence.

Catalyst 3550 as an Access-Layer Sw itch The Catalyst 3550 family of switches supports enhanced QoS features that can be used in the access layer. Of particular interest are the Catalyst 3550's ability to classify and mark traffic on ingress to the network using ACLs and policies. The Catalyst 3550's ability to identify traffic flows at Layer 3 and Layer 4 using ACLs makes it very powerful as an access-layer device. The Catalyst 3550 is a powerful, QoS-capable switch for the access layer. However, it does not support the full set of features required for an IP telephony deployment. The Catalyst 3550 IOS software provides full support for IP telephony. However, there is no hardware option that provides inline power. This can be designed around through the use of the AC power brick or an inline power patch panel. The inline power feature is scheduled for addition to the Catalyst 3550 family sometime in CY2002. Figure 3-11 shows a general model for the Catalyst 3550 as an access device (as illustrated in the QoS configurations discussed in this chapter). Figure 3-11 General M odel for Catalyst 3550 QoS Configurations

Si

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Catalyst 6500

Catalyst 3550

Access

VLAN=12

74702

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This section presents suggested configurations for port scheduling and queuing on the Catalyst 3550. In general: •

The recommended configuration for the receive interface is 1Q-FIFO—one standard FIFO queue.

•

The recommended configuration for the transmit interface is 1P3Q1T—one priority queue and three queues, each with a single drop threshold. Scheduling is done on a WRR basis where each queue is given a relative weight while the priority queue is serviced exhaustively. The default is WRR only. If priority scheduling is required, it must be explicitly enabled. Admission to the queues is based on 802.1p CoS or port priority CoS. The default queue admission criteria for the Catalyst 3550 are as follows: queue 1: CoS 0 and 1; queue 2: CoS 2 and 3; queue 3: CoS 4 and 5; queue 4: CoS 6 and 7.

For the Catalyst 3550, QoS requires the following changes to the access switch configuration: 1. Enable QoS globally. 2. Modify the default CoS-to-DSCP mapping table. 3. Turn on priority queuing. 4. Move CoS 5 traffic to the priority queue. 5. Enable QoS features when classification is required. 6. Enable QoS features when connecting and IP phone. 7. Enable QoS features for the uplink to distribution.

Enabling QoS To enable QoS on the access-layer Catalyst 3550, do the following: Step 1

Enable switch-wide QoS. 3550G-Access(config)#mls qos

M odifying the CoS-to-DSCP M appings There are 8 CoS labels and 64 possible DSCP labels. To trust the CoS markings, the default CoS-to-DSCP mapping table must be modified to equate CoS 3 (VoIP control traffic) to AF31, CoS 5 (VoIP bearer traffic) to EF, and CoS 4 to AF41. Step 1

The default CoS-to-DSCP mapping is as follows: 3550G-Access#show mls qos maps Cos-dscp map: cos: 0 1 2 3 4 5 6 7 -------------------------------dscp: 0 8 16 24 32 40 48 56

Change the default mapping table so that CoS 3 = AF31, CoS 4 = AF41, and CoS 5 = EF. Remember to use the decimal equivalents. 3550G-Access(config)#mls qos map cos-dscp 0 8 16 26 34 46 48 56

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Enabling Priority Queuing To enable priority queuing, do the following: Step 1

Specify the interface range. 3550G-Access(config)#interface range g 0/1 - 12

Step 2

Specify the priority queue. 3550G-Access(config-if-range)#priority-queue out

Step 3

Move the CoS 5 traffic to queue 4, which is the priority queue for the Catalyst 3500 family. 3550G-Access(config-if-range)#wrr-queue cos-map 4 5

Configuring ACLs There are times when classification of traffic by the access-layer switch is required. The Catalyst 3550 has a powerful set of features that allow us to classify traffic as it enters the network. The following configuration illustrates how to classify VoIP bearer and control traffic with the Catalyst 3550 as it enters the network. Step 1

Create the ACLs to identify the traffic. 3550G-Access(config)#ip access-list extended VOICE 3550G-Access(config-ext-nacl)#remark Match the UDP ports that VoIP Uses for Bearer Traffic 3550G-Access(config-ext-nacl)#permit udp any any range 16384 32767 3550G-Access(config)#ip access-list extended VOICE-CONTROL 3550G-Access(config-ext-nacl)#remark Match VoIP Control Traffic 3550G-Access(config-ext-nacl)#remark SCCP 3550G-Access(config-ext-nacl)#permit tcp any any range 2000 2002 3550G-Access(config-ext-nacl)#remark H323 Fast Start 3550G-Access(config-ext-nacl)#permit tcp any any eq 1720 3550G-Access(config-ext-nacl)#remark H323 Slow Start - Verify could be in 3000 range for CM or 11000 to 65535 with newer IOS's 3550G-Access(config-ext-nacl)#permit tcp any any range 11000 11999 3550G-Access(config-ext-nacl)#remark H323 MGCP 3550G-Access(config-ext-nacl)#permit udp any any eq 2427

Step 2

Create classes that use the ACLs as admission criteria. 3550G-Access(config)#class-map match-all VOICE 3550G-Access(config-cmap)#description VOIP Bearer Traffic 3550G-Access(config-cmap)#match access-group name VOICE 3550G-Access(config)#class-map match-all VOICE-CONTROL 3550G-Access(config-cmap)#description VOIP Control Traffic (SCCP, H225, H254, MGCP) 3550G-Access(config-cmap)#match access-group name VOICE-CONTROL

Step 3

Create a policy to set the DSCP PHB label/value for the classes. 3550G-Access(config)#policy-map ACCESS-C3550-LAN-EDGE-IN 3550G-Access(config-pmap)#description Set DSCP PerHopBehavior Label for VOIP Control and Bearer Traffic 3550G-Access(config-pmap)#class VOICE-CONTROL 3550G-Access(config-pmap-c)#set ip dscp 26 3550G-Access(config-pmap)#class VOICE 3550G-Access(config-pmap-c)#set ip dscp 46

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Step 4

Apply the policy to an interface so that traffic entering the network through this port is classified with the appropriate DSCP PHB Label EF and AF31 for VoIP bearer and control respectively. 3550G-Access(config)#int g 0/2 3550G-Access(config-if)#service-policy input ACCESS-C3550-LAN-EDGE-IN

Configuring Access-Layer Phone Support When the Catalyst 3550 is connected to an IP phone, you must do the following: Step 1

Configure the switch to trust CoS from the IP phone. 3550G-Access(config)#interface g 0/11 3550G-Access(config-if)#mls qos trust cos

Step 2

Enable the voice and data VLANs. 3550G-Access(config-if)#switchport voice vlan 111 3550G-Access(config-if)#switchport access vlan 11

Step 3

Set the IP phone’s trust boundary. 3550G-Access(config-if)#switchport priority extend cos 0

Step 4

Enable priority queuing on the port. 3550G-Access(config-if)#priority-queue out

Step 5

Modify the CoS to queue admission criteria. 3550G-Access(config-if)#wrr-queue cos-map 4 5

Configuring the Uplink to the Distribution Sw itch The ports attached to the distribution layer require a slightly different configuration. These ports must be configured to trust DSCP or CoS depending on the capabilities of the distribution-layer switch attached. In the following configuration, port 0/11 is attached to a Layer 3-aware distribution device and can trust DSCP arriving from it. Port 0/12 illustrates and example where CoS-only classification is used.

Note

Step 1

The system-wide CoS-to-DSCP mapping and DSCP-to-queue admission criteria configurations must have been completed and the priority queue must be enabled for these ports in order for the access-layer uplink ports to perform QoS as expected.

Configure CoS trust. 3550G-Access(config)#interface g 0/11 3550G-Access(config-if)#mls qos trust cos

Step 2

Enable the priority queue on this interface and move CoS 5 traffic into queue 4, which is the priority queue on the Catalyst 3500 family. 3550G-Access(config-if)#priority-queue out 3550G-Access(config-if)#wrr-queue cos-map 4 5

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Step 3

Configure DSCP trust. 3550G-Access(config)#interface g 0/12 3550G-Access(config-if)#mls qos trust dscp

Step 4

Enable the priority queue on this interface and move Cos 5 traffic into queue 4, which is the priority queue on the Catalyst 3500 family. 3550G-Access(config-if)#priority-queue out 3550G-Access(config-if)#wrr-queue cos-map 4 5

Verifying the Configuration On the Catalyst 3550 access-layer switch, you can verify the configuration and performance during periods of high congestion by examining the output of the following commands: Command

Description

See

show qos map cos

Displays the QoS CoS mapping information.

Example 3-13

show mls qos interface queueing

Displays the QoS queuing strategy.

Example 3-14

show policy-map interface

Displays statistics and configurations of input and output policies attached to an interface.

Example 3-15

Example 3-13 Displaying QoS CoS M apping Information 3550G-Access#show mls qos maps Cos-dscp map: cos: 0 1 2 3 4 5 6 7 -------------------------------dscp: 0 8 16 26 34 46 48 56

Example 3-14 Displaying QoS Queuing Strategy 3550G-Access#show mls qos interface queueing GigabitEthernet0/1 Ingress expedite queue: dis Egress expedite queue: ena wrr bandwidth weights: qid-weights 1 - 25 2 - 25 3 - 25 4 - 25 when expedite queue is disabled Dscp-threshold map: d1 : d2 0 1 2 3 4 5 6 7 8 9 --------------------------------------0 : 01 01 01 01 01 01 01 01 01 01 1 : 01 01 01 01 01 01 01 01 01 01 2 : 01 01 01 01 01 01 01 01 01 01 3 : 01 01 01 01 01 01 01 01 01 01 4 : 01 01 01 01 01 01 01 01 01 01 5 : 01 01 01 01 01 01 01 01 01 01 6 : 01 01 01 01

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Cos-queue map: cos-qid 0 - 1 1 - 1 2 - 2 3 - 2 4 - 3 5 - 4 6 - 4 7 - 4

Example 3-15 Displaying Policy Information 3550G-Access#show policy-map interface g 0/2 service-policy input: ACCESS-C3550-LAN-EDGE-IN class-map: VOICE-CONTROL (match-all) 0 packets, 0 bytes 5 minute offered rate 0 bps, drop rate 0 bps match: access-group name VOICE-CONTROL class-map: VOICE (match-all) 0 packets, 0 bytes 5 minute offered rate 0 bps, drop rate 0 bps match: access-group name VOICE class-map: class-default (match-any) 0 packets, 0 bytes 5 minute offered rate 0 bps, drop rate 0 bps match: any 0 packets, 0 bytes 5 minute rate 0 bps

Catalyst 2950 as an Access-Layer Sw itch The 2950 family of Catalyst switches support enhanced QoS features that can be used in the access layer. Of particular interest is the ability to classify and mark traffic on ingress to the network via ACLs and policies. While not as advanced as the Catalyst 4000 Supervisor III or Catalyst 3550 in its flexibility to identify traffic flows at Layer 3 and Layer 4 via ACLs, the Catalyst 2950 family of switches are Layer 3 aware, making them very powerful. It should be noted that ACLs used to identify traffic in the Catalyst 2950 are limited to a single TCP or UDP port per Access Control Entry (ACE). Use of the range, greater than, or less than, keywords is not supported when defining an ACL on the Catalyst 2950. This can make identification of applications that use a wide range of ports difficult. This means that long ACLs are required, which may exceed the Catalyst 2950's ACL memory capacity. The Catalyst 2950 is a very powerful QoS-capable switch for the access layer. However, it does not support the full set of features required for an IP telephony deployment. The Catalyst 2950 IOS software provides full support for IP telephony. There is not, however, a Catalyst 2950 hardware option that provides inline power. This can be designed around through the use of the AC power brick or an inline power patch panel. Figure 3-12 shows a general model for the Catalyst 2950 as an access device (as illustrated in the QoS configurations discussed in this chapter).

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Figure 3-12 General M odel for Catalyst 2950 QoS Configurations

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Catalyst 2950

Access

VLAN=12

74703

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This section presents suggested configurations for port scheduling and queuing on the Catalyst 2950. In general: •

The recommended configuration for the receive interface is 1Q-FIFO—one standard FIFO queue.

•

The recommended configuration for the transmit interface is 4Q1T—four standard queues with a single threshold. Scheduling is done on a priority-scheduling basis or a WRR scheduling algorithm. The default is priority scheduling. Admission to the queues is based on 802.1p CoS or port priority CoS. The default queue admission criteria for the Catalyst 2950 are as follows: queue 1: CoS 0 and 1, queue 2: CoS 2 and 3, queue 3: CoS 4 and 5, queue 4: CoS 6 and 7.

For the Catalyst 2950, QoS requires the following changes to the access switch configuration: 1. Modify the default CoS-to-DSCP mapping table. 2. Configure an ACL that identifies mission critical traffic, associate it with a service policy, and apply

the policy to an interface. 3. Enable QoS features to support an IP Phone. 4. Enable QoS features required to support uplink to distribution layer.

Note

QoS is on by default in the Catalyst 2950. Priority queuing is the default. No change is required for the CoS-to-queue assignment.

M odifying the CoS-to-DSCP M appings There are 8 CoS labels and 64 possible DSCP labels. To trust the CoS markings, the default CoS-to-DSCP mapping table must be modified to equate CoS 3 (VoIP control traffic) to AF31, CoS 5 (VoIP bearer traffic) to EF, and CoS 4 to AF41.

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Step 1

The default CoS-to-DSCP mapping is as follows: 2950-Access#sh mls qos maps Dscp-cos map: dscp: 0 8 10 16 18 24 26 32 34 40 46 48 56 ----------------------------------------------cos: 0 1 1 2 2 3 3 4 4 5 5 6 7 Cos-dscp map: cos: 0 1 2 3 4 5 6 7 -------------------------------dscp: 0 8 16 24 32 40 48 56

Change the default mapping table so that CoS 2 = AF21, CoS 3 = AF31, CoS 5 = EF. Remember to use the decimal equivalents. 2950-Access(config)#mls qos map cos-dspc 0 8 16 26 34 46 48 56

Configuring ACLs To use ACLs to determine admission criteria, do the following: Step 1

Define an access list to select the traffic that will be classified later. 2950-Access(config)#ip access-list extended GOLD-DATA 2950-Access(config-ext-nacl)#remark Match IP Address of the application server 2950-Access(config-ext-nacl)#permit ip any host 192.168.100.1

Step 2

Define a class that to use in the policy. 2950-Access(config)#class-map match-all GOLD-DATA 2950-Access(config-cmap)#description Mission Critical Traffic 2950-Access(config-cmap)#match access-group name GOLD-DATA

Step 3

Define the policy that uses the ACL and class and sets the DSCP PHB label. 2950-Access(config)#policy-map ACCESS-C2950-LAN-EDGE-IN 2950-Access(config-pmap)#description Set DSCP PerHopBehavior Label for Mission Critical Traffic 2950-Access(config-pmap)#class GOLD-DATA 2950-Access(config-pmap-c)#set ip dscp 18

Step 4

Apply the policy to an interface. In this example, all traffic that matches the ACL will be classified with a DSCP PHB of AF21. 2950-Access(config)#int fa0/1 2950-Access(config-if)#service-policy input ACCESS-C2950-LAN-EDGE-IN

Configuring Access-Layer Phone Support When the Cisco 2950 is connected to an IP phone, you must do the following:

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Step 1

Configure the switch to trust CoS from the IP phone. 2950G-Access(config)#interface g 0/11 2950G-Access(config-if)#mls qos trust cos

Step 2

Enable the voice and data VLANs. 2950G-Access(config-if)#switchport voice vlan 111 2950G-Access(config-if)#switchport access vlan 11

Step 3

Set the IP phone’s trust boundary. 2950G-Access(config-if)#switchport priority extend cos 0

Configuring the Uplink to the Distribution Sw itch The ports attached to the distribution layer require a different configuration. These ports must be configured to trust DSCP or CoS depending on the capabilities of the distribution-layer switch attached. In the following configuration, port 0/11 illustrates an example where CoS-only classification is used. Port 0/12 is attached to a Layer 3-aware distribution device and can trust the DSCP arriving from it. Step 1

Configure DSCP trust. 2950G-Access(config)#interface g 0/11 2950G-Access(config-if)#mls qos trust cos

Step 2

Configure CoS trust. 2950G-Access(config)#interface g 0/12 2950G-Access(config-if)#mls qos trust dscp

Verifying the Configuration On the Catalyst 2950 access-layer switch, you can verify the configuration by examining the output of the following commands: Command

Description

See

show mls qos maps

Displays the QoS CoS mapping information.

Example 3-16

show wrr-queue band

Displays the queuing mechanism and the QoS Example 3-17 queue assignments.

Example 3-16 Displaying QoS CoS M apping Information 2950-Access#show mls qos maps Dscp-cos map: dscp: 0 8 10 16 18 24 26 32 34 40 46 48 56 ----------------------------------------------cos: 0 1 1 2 2 3 3 4 4 5 5 6 7 Cos-dscp map: cos: 0 1 2 3 4 5 6 7 -------------------------------dscp: 0 8 16 26 34 46 48 56

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Example 3-17 Displaying the Queuing M echanism and Queue Assignments 2950-Access#show wrr-queue band wrr-queue bandwidth is disabled 2950-Access#show wrr-que cos CoS Value : 0 1 2 3

4

5

6

7

Priority Queue :

3

3

4

4

1

1

2

2

Selecting a Distribution-Layer Sw itch There are many choices for distribution-layer Catalyst switches. The most common switch in this layer of a hierarchical network design is the Catalyst 6500. The Catalyst 6500 series has advanced QoS features via the PFC that makes it an ideal choice for this location in the network. The Catalyst 4000 with Supervisor III is also well suited for this task. The primary difference between a Catalyst 6500 series and the Catalyst 4000 when used in this part of a network design is scalability. The Catalyst 6500 can scale to 256 Gbps with 10 Gbps interfaces while the Catalyst 4000 with Supervisor III can only scale to 32 Gbps interfaces. Additionally, for very small networks (where density, scalability, and investment protection are not a primary concern), the Catalyst 3550 family of switches offers a robust QoS feature set that makes it a good fit for the distribution layer. After you configure the access switch and attached it to the distribution layer, you must set up QoS on the distribution switches. This section illustrates how to do that on the various switches mentioned earlier in this chapter.

Catalyst 6500 (w ith Catalyst OS) as a Distribution-Layer Sw itch Figure 3-13 shows a general model for the Catalyst 6500 (with Catalyst OS) as a distribution device (as illustrated in the QoS configurations discussed in this chapter).

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Figure 3-13 General M odel for Catalyst 6500 (w ith Catalyst OS) as a Distribution Sw itch in QoS Configurations

Native IOS 6500

Distribution

Si

2/1

Hybrid 6500 1/1

3/1

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IP

IP

VLAN=10

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VVID=112 IP

VLAN=12

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For the Catalyst 6500 running Catalyst OS, QoS requires the following changes to the configuration of the distribution switch: 1. Configure VoIP control traffic transmit queuing. 2. Configure the distribution layer with a Layer 3 access switch. 3. Configure the distribution layer with a Layer 2 access switch.

Configuring the Distribution Layer VoIP Control Traffic Transmit Queue When QoS is enabled, all VoIP (CoS of 5) traffic is placed into the egress interface priority queue on 1p2q2t interfaces and into queue 2 on 2q2t interfaces (for all versions “1” of the 10/100 line cards). To configure the Catalyst 6500 CoS queue admission rules to ensure that VoIP control traffic (CoS of 3) is placed into the second queue, do the following: Step 1

Change the mapping for the 1p2q2t interfaces. cat6k-distrib> (enable) set qos map 1p2q2t tx 2 1 cos 3

Step 2

Change the mapping for the 2q2t interfaces. cat6k-distrib> (enable) set qos map 2q2t tx 2 1 cos 3

Configuring the Distribution Layer w ith a Layer 3 Sw itch Once you have enabled QoS on the distribution layer switch and have modified the default queue admission, do the following to complete the integration with a Layer 3 access switch:

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Step 1

Enable trust for DSCP values from adjacent Layer 3 access switches. Use port-based QoS on the trunking port and use trust-dscp instead of trust-cos (because trust-cos overwrites the Layer 3 DSCP value with the mapped CoS, which is unnecessary because classification is done at the access layer). cat6k-distrib> (enable) set port qos 1/1 port-based cat6k-distrib> (enable) set port qos 1/1 trust trust-dscp

Step 2

Configure CoS/IP Precedence-to-DSCP mappings. Cisco follows the IETF recommendations for setting the DSCP classification values for both the VoIP control plane traffic and VoIP bearer or media plane traffic. The recommended settings are DSCP of AF31 for VoIP control plane and DSCP of EF for VoIP bearer plane. To map the Layer 3 IP Precedence settings correctly to these DSCP values, you must modify the default CoS/IP Precedence-to-DSCP mappings as follows: cat6k-distrib> (enable) set qos ipprec-dscp-map 0 8 16 26 34 46 48 56

Configuring the Distribution Layer w ith a Layer 2 Sw itch Once you have enabled QoS on the distribution-layer switch and have modified the default queue admission, do the following to complete the integration with a Layer 2 access switch: Step 1

Enable trust for CoS values from adjacent Layer 2 access switches. Use port-based QoS on the trunking port and use trust-cos instead of trust-dscp. This configuration is used when the access-layer switch is a Layer 2-only device performing CoS classification. cat6k-distrib> (enable) set port qos 1/2,3/2 trust trust-cos

Step 2

Configure CoS-to-DSCP mappings. Cisco follows the IETF recommendations for setting the DSCP classification values for both the VoIP control plane traffic and VoIP bearer or media plane traffic. The recommended settings are DSCP of AF31 for VoIP control plane and DSCP of EF for VoIP bearer plane. Modify the default CoS-to-DSCP mappings as follows: cat6k-distrib> (enable) set qos cos-dscp-map 0 8 16 26 34 46 48 56

Configuring QoS Policies and Layer 3 Access Lists for VoIP Control Traffic In addition, you must configure Layer 3 access lists for VoIP control traffic.

Note

Step 1

This example uses the ACL_IP-PHONES ACL defined earlier.

Inform the port that all QoS associated with the port will be done on a VLAN basis to simplify configuration. cat6k-distrib> (enable) set port qos 1/2,3/2 vlan-based

Step 2

Map the ACL_IP-PHONE ACL to the auxiliary VLAN. cat6k-distrib> (enable) set qos acl map ACL_IP-PHONES 111

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To verify the settings, issue the following commands: cat6k-distrib> (enable) show qos ACL name -------------------------------ACL_IP-PHONES ACL name -------------------------------ACL_IP-PHONES

acl map run ACL_IP-PHONES Type Vlans ---- --------------------------------IP 110,111,112 Type Ports ---- --------------------------------IP

cat6k-distrib> (enable) show qos acl info run ACL_IP-PHONES set qos acl IP ACL_IP-PHONES ---------------------------------------------1. dscp 26 tcp any any range 2000 2002 2. dscp 26 tcp any any eq 1720 3. dscp 26 tcp any any range 11000 11999 4. dscp 26 udp any any eq 2427 5. trust-cos any

Step 3

Enable trust for DSCP values from adjacent Layer 3 access switches. Use port-based QoS on the trunking port. Current 10/100 version 1 linecards must have trust-ipprec enabled even though the parser returns an error. cat6k-distrib> (enable) set port qos 9/1 port-based cat6k-distrib> (enable) set port qos 9/1 trust trust-ipprec

Step 4

Create an access list that accepts incoming Layer 3 IP Precedence classification. cat6k-distrib> (enable) set qos acl ip ACL_TRUST-WAN trust-ipprec any

Step 5

Write the ACL to hardware. cat6k-distrib> (enable) commit qos acl ACL_TRUST-WAN

Step 6

Map the ACL_TRUST-WAN ACL to the port. cat6k-distrib> (enable) set qos acl map ACL_TRUST-WAN 9/1

Verifying the Configuration On the Catalyst 6500 distribution-layer switch (with Catalyst OS), you can verify the configuration by examining the output of the following commands: Command

Description

See

show qos map run ipprec-dscp-map

Displays the QoS IP Precedence mapping information.

Example 3-18

show qos map run cos-dscp-map

Displays the QoS CoS mapping information.

Example 3-19

show port qos

Displays the Qos settings for a specified port.

Example 3-20

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Example 3-18 Displaying the QoS IP Precedence-to-DSCP M appings cat6k-distrib> (enable) show qos map run ipprec-dscp-map IP-Precedence - DSCP map: IP-Prec DSCP ---------0 0 1 8 2 16 26 = AF31 VoIP Control 3 26 4 34 34 = AF41 IP Video Conferencing 5 46 46 = EF VoIP Bearer 6 48 7 56

Example 3-19 Displaying the QoS CoS-to-DSCP M appings cat6k-distrib> (enable) show qos map run cos-dscp-map CoS - DSCP map: CoS DSCP -----0 0 1 8 2 16 3 26 4 34 5 46 6 48 7 56

Example 3-20 Displaying the QoS Port Settings cat6k-distrib> (enable) show port qos 9/1 QoS is enabled for the switch. QoS policy source for the switch set to local. Port

Interface Type Interface Type Policy Source Policy Source config runtime config runtime ----- -------------- -------------- ------------- ------------9/1 port-based port-based COPS local Port TxPort Type RxPort Type Trust Type Trust Type Def CoS Def CoS config runtime config runtime -------------------------------------------------------------------9/1 2q2t 1q4t trust-ipprec trust-ipprec 0 0 Port Ext-Trust Ext-Cos ----- --------- ------9/1 untrusted 0 (*)Runtime trust type set to untrusted. Config: Port ACL name Type ----- -------------------------------- ---9/1 ACL_TRUST-WAN IP Runtime: Port ACL name Type ----- -------------------------------- ---9/1 ACL_TRUST-WAN IP

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Catalyst 6500 (w ith Native IOS) as a Distribution-Layer Sw itch Figure 3-14 shows a general model for the Catalyst 6500 (with Native IOS) as a distribution device (as illustrated in the QoS configurations discussed in this chapter). Figure 3-14 General M odel for Catalyst 6500 (w ith Native IOS) as a Distribution Sw itch in QoS Configurations

Native IOS 6500

Distribution

Si

2/1

Hybrid 6500 1/1

3/1

2/2

Si

1/2

6500 w/ PFC

7200 WAN router

9/1 3/2

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IP

IP

VLAN=10

VLAN=11

VVID=112 IP

VLAN=12

74705

VVID=110

For the Catalyst 6500 running Native IOS, QoS requires the following changes to the configuration of the distribution switch: 1. Configure QoS. 1. Configure VoIP control traffic transmit queuing. 2. Configure the distribution layer with a Layer 3 access switch. 3. Configure the distribution layer with a Layer 2 access switch. 4. Configure QoS policies and Layer 3 access lists for VoIP control traffic classification.

Enabling QoS To enable QoS on the Catalyst 6500 with Native Cisco IOS, do the following: Step 1

Enable QoS. Cat6k-distrib (config)#mls qos

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Configuring the Distribution Layer VoIP Control Traffic Transmit Queue When QoS is enabled, all VoIP (CoS of 5) traffic is placed into the egress interface priority queue on 1p2q2t interfaces and into queue 2 on 2q2t interfaces (for all versions “1” of the 10/100 line cards). To configure the Catalyst 6500 CoS queue admission rules to ensure that VoIP control traffic (CoS of 3) is placed into the second queue, do the following: Step 1

Specify the range of ports for which you want to define queue admission rules. Cat6k-distrib (config)#interface range gigabitEthernet 1/1 - 2

Step 2

Map the CoS values to drop thresholds for each queue. Cat6k-distrib (config-if)#wrr-queue cos-map 2 1 3 4

Tip

When using IOS version 12.1(8a)EX and above on a Catalyst 6500, you cannot modify the CoS-to-queue mapping for the priority queue on the Gigabit Ethernet ports in the supervisor module. For more information, please see the field notice titled Limited QoS Functionality on the Gigabit Ethernet Ports on the Catalyst 6000 Supervisor.

Configuring the Distribution Layer w ith a Layer 3 Sw itch Once you have enabled QoS on the Native Cisco IOS distribution layer switch and have modified the default queue admission, do the following to complete the integration with a Layer 3 access switch: Step 1

Enable trust for DSCP values from adjacent Layer 3 access switches. Use port-based QoS on the trunking port (port-based QoS is enabled by default when MLS QoS is configured) and use mls qos trust dscp. Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib

Step 2

(config)#interface GigabitEthernet2/1 (config-if)#no ip address (config-if)#wrr-queue cos-map 2 1 3 4 (config-if)#mls qos trust dscp (config-if)#switchport (config-if)#switchport trunk encapsulation dot1q (config-if)#switchport mode trunk

Configure CoS/IP Precedence-to-DSCP mappings. Cisco follows the IETF recommendations for setting the DSCP classification values for both the VoIP control plane traffic and VoIP bearer or media plane traffic. The recommended settings are DSCP of AF31 for VoIP control plane and DSCP of EF for VoIP bearer plane. Additionally, the recommended value for video conferencing (CoS 4) is DSCP AF41 (decimal 34). The default CoS-to-DSCP mapping equates CoS 4 with DSCP decimal 32. Therefore, to support video conferencing, the mapping must be modified to map CoS 4 to DSCP decimal 34 (AF41). To map the Layer 3 IP Precedence settings correctly to these DSCP values, modify the default CoS/IP Precedence-to-DSCP mappings as follows: Cat6k-distrib (config-if)#mls qos map ip-prec-dscp 0 8 16 26 34 46 48 56

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Configuring the Distribution Layer w ith a Layer 2 Sw itch Once you have enabled QoS on the distribution-layer switch and have modified the default queue admission, do the following to complete the integration with a Layer 2 access switch: Step 1

Step 2

Enable trust for CoS values from adjacent Layer 2 access switches. Use port-based QoS on the trunking port and use mls qos trust cos. This configuration is used when the access-layer switch is only a Layer 2 device performing CoS classification. Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib

(config)#interface GigabitEthernet2/2 (config-if)#no ip address (config-if)#wrr-queue cos-map 2 1 3 4 (config-if)#mls qos vlan-based (config-if)#mls qos trust cos (config-if)#switchport (config-if)#switchport trunk encapsulation dot1q (config-if)#switchport mode trunk

Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib

(config)#interface GigabitEthernet3/1 (config-if)#no ip address (config-if)#wrr-queue cos-map 2 1 3 4 (config-if)#mls qos vlan-based (config-if)#mls qos trust cos (config-if)#switchport (config-if)#switchport trunk encapsulation dot1q (config-if)#switchport mode trunk

Configure CoS-to-DSCP mappings. Cisco follows the IETF recommendations for setting the DSCP classification values for both the VoIP control plane traffic and VoIP bearer or media plane traffic. The recommended settings are DSCP of AF31 for VoIP control plane and DSCP of EF for VoIP bearer plane. To map the Layer 2 settings correctly to these DSCP values, you must modify the default CoS-to-DSCP mappings as follows: Cat6k-distrib (config-if)#mls qos map cos-dscp 0 8 16 26 34 46 48 56

Configuring QoS Policies and Layer 3 Access Lists for VoIP Control Traffic In addition, you must configure QoS policies and Layer 3 access lists for VoIP control traffic. The QoS configuration for the Catalyst 6500 with Native Cisco IOS is similar to the QoS configuration for Cisco WAN routers, except how policing is used for marking traffic flows and how service policies are applied to VLAN interfaces. With Native Cisco IOS: •

The physical gigabit Ethernet uplink ports are configured to use VLAN-based QoS with the MLS QoS VLAN-based Native Cisco IOS interface commands.

•

The service-policy is applied to all VLAN traffic inbound on the uplink.

In the example below, three classes are defined: one for the VoIP media stream, one for the control traffic, and one for all other traffic. Traffic is filtered for these classes based on the Layer 3 or 4 source and destination IP addresses and ports. Each of these classes is referenced in the Voice-QoS policy map. In the policy-map statements, a policing function is used to classify all traffic that meets the entrance criteria matched with the class-map access lists. The Catalyst 6500 Native Cisco IOS software does not support the set ip dscp commands. Although it can be enabled, it should not be used because only software switched packets will be classified. Instead, the policing algorithm should be used to classify traffic.

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In this scenario, the policing code tags the traffic flows with DSCP values of AF31 for VoIP control traffic, EF for VoIP bearer traffic, and 0 for all other packets. Step 1

Create classes that use ACLs as admission criteria. Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib

Step 2

(config)#class-map match-all VOICE-CONTROL (config-cmap)#match access-group 100 (config)#class-map match-all VOICE (config-cmap)#match access-group 101 (config)#class-map match-all BEST-EFFORT-DATA (config-cmap)#match access-group 102

Create policies to tag the traffic flows with the appropriate DSCP values.

Note

The policer value (4000000000) below should be sized appropriately in your network.

Cat6k-distrib (config)#policy-map DISTRIBUTION-C6000-UPLINK-IN Cat6k-distrib (config-pmap)#class VOICE-CONTROL Cat6k-distrib (config-pmap-c)#police 4000000000 125000000 125000000 conform-action set-dscp-transmit 26 exceed-action transmit Cat6k-distrib (config-pmap)#class VOICE Cat6k-distrib (config-pmap-c)#police 4000000000 125000000 125000000 conform-action set-dscp-transmit 46 exceed-action transmit Cat6k-distrib (config-pmap)#class BEST-EFFORT-DATA Cat6k-distrib (config-pmap-c)#police 4000000000 125000000 125000000 conform-action set-dscp-transmit 0 exceed-action transmit

Step 3

Create an access list for VoIP control traffic. Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib

Step 4

(config)#access-list (config)#access-list (config)#access-list (config)#access-list

100 100 100 100

permit permit permit permit

tcp tcp tcp udp

any any any any

any any any any

range 2000 2002 eq 1720 range 11000 11999 eq 2427

Create an access list for VoIP bearer traffic. Cat6k-distrib (config)#access-list 101 permit udp any any range 16384 32767

Step 5

Create an access list for best effort traffic. Cat6k-distrib (config)#access-list 102 permit ip any any

Step 6

Enable trust for DSCP values from adjacent Layer 3 access switches. Use VLAN-based QoS on the trunking port. Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib

(config)#interface GigabitEthernet2/2 (config-if)#no ip address (config-if)#wrr-queue cos-map 2 1 3 4 (config-if)#mls qos vlan-based (config-if)#switchport (config-if)#switchport trunk encapsulation dot1q (config-if)#switchport mode trunk

Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib

(config)#interface GigabitEthernet3/1 (config-if)#no ip address (config-if)#wrr-queue cos-map 2 1 3 4 (config-if)#mls qos vlan-based (config-if)#switchport (config-if)#switchport trunk encapsulation dot1q (config-if)#switchport mode trunk

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Step 7

Configure the voice VLANs on the access switches. Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib

(config)#interface Vlan111 (config-if)#ip address 10.1.111.77 255.255.255.0 (config-if)#ip helper-address 10.1.10.10 (config-if)#no ip redirects (config-if)#service-policy input DISTRIBUTION-C6000-UPLINK-IN (config-if)#standby 111 ip 10.1.111.1

Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib Cat6k-distrib

(config)#interface Vlan112 (config-if)#description voice vlan on 3500 (config-if)#ip address 10.1.112.77 255.255.255.0 (config-if)#ip helper-address 10.1.10.10 (config-if)#no ip redirects (config-if)#service-policy input DISTRIBUTION-C6000-UPLINK-IN (config-if)#standby 112 ip 10.1.112.1

Verifying the Configuration To verify the QoS configuration, issue the following command. Cat6k-distrib#show mls qos QoS is enabled globally Microflow policing is enabled globally QoS is vlan-based on the following interfaces: Vl111 V112 Gi2/2 Gi3/1 Gi3/2 Gi3/3 Gi3/4 Gi3/5 Gi3/6 Gi3/7 Gi3/8 Gi4/1 Gi4/2 Gi4/3 Gi4/4 Gi4/5 Gi4/6 Gi4/7 Gi4/8 Fa9/1 Fa9/2 Fa9/3 Fa9/4 Fa9/5 Fa9/6 Fa9/7 Fa9/8 Fa9/9 Fa9/10 Fa9/11 Fa9/12 Fa9/13 Fa9/14 Fa9/15 Fa9/16 Fa9/17 Fa9/18 Fa9/19 Fa9/20 Fa9/21 Fa9/22 Fa9/23 Fa9/24 Fa9/25 Fa9/26 Fa9/27 Fa9/28 Fa9/29 Fa9/30 Fa9/31 Fa9/32 Fa9/33 Fa9/34 Fa9/35 Fa9/36 Fa9/37 Fa9/38 Fa9/39 Fa9/40 Fa9/41 Fa9/42 Fa9/43 Fa9/44 Fa9/45 Fa9/46 Fa9/47 Fa9/48 QoS global counters: Total packets: 16750372458300 Packets dropped by policing: 55930847232 IP packets with TOS changed by policing: 16750372458300 IP packets with COS changed by policing: 55945330688 Non-IP packets with COS changed by policing: 16750372458300

Catalyst 4000 w ith Supervisor III as a Distribution-Layer Sw itch Figure 3-15 shows a general model for the Catalyst 4000 with Supervisor III as a distribution device (as illustrated in the QoS configurations discussed in this chapter).

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Figure 3-15 General M odel for Catalyst 4000 w ith Supervisor III as a Distribution Sw itch in QoS Configurations

4k Sup III

Distribution

Si

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7200 WAN router

4k Sup III 3/1

3/3

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VLAN=10

IP

VLAN=11

VVID=112 IP

VLAN=12

74706

VVID=110

For a Catalyst 4000 with Supervisor III, QoS requires the following changes to the configuration of the distribution switch: 1. Enable QoS. 2. Change the default CoS-to-DSCP mapping table so that CoS and DSCP PHB label behavior can be

maintained throughout the network. 3. Configure service policies to classify traffic for that does not contain a CoS-to-ToS marking that

you can trust. 4. Enable CoS or DSCP trust on the ports where trust is appropriate. Use ToS for Layer 3 aware access

and CoS for Layer 2 only access.

Enabling QoS To enable QoS on the Catalyst 4000, do the following: Step 1

Enable QoS. 4006-SUPIII-Dist(config)#qos

M odifying the CoS-to-DSCP M apping The default CoS-to-DSCP maps must be modified to allow us to trust CoS and maintain DSCP PHB EF and AF31 for VoIP bearer and control traffic respectively.

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Step 1

The default CoS-to-DSCP mapping is as follows: 4006-SUPIII-Dist#show qos map cos CoS-DSCP Mapping Table CoS: 0 1 2 3 4 5 6 7 -------------------------------DSCP: 0 8 16 24 32 40 48 56

Change the default CoS-to-DSCP mapping so that CoS 5 = EF and CoS 3 = AF31 and CoS 4 = AF41. 4006-SUPIII-Dist(config)#qos map cos 3 to dscp 26 4006-SUPIII-Dist(config)#qos map cos 4 to dscp 34 4006-SUPIII-Dist(config)#qos map cos 5 to dscp 46

Configuring Priority Queuing Turn on priority queuing on a per port basis. Default admission to the priority queue matches our requirements. Step 1

Specify the transmit queue. 4006-SUPIII(config-if-tx-queue)#tx-queue 3

Step 2

Set the priority for the queue to high. 4006-SUPIII(config-if-tx-queue)#priority high

Configuring ACLs Create an ACL to identify the traffic to be marked and create classes that use the ACLs as admission criteria. Step 1

Create an ACL to match the traffic you want to prioritize. 4006-SUPIII-Dist(config)#ip access-list extended GOLD-DATA 4006-SUPIII-Dist(config-ext-nacl)#remark Match IP Address of the application server 4006-SUPIII-Dist(config-ext-nacl)#permit ip any host 192.168.100.1 4006-SUPIII-Dist(config-ext-nacl)#permit ip host 192.168.100.1 any 4006-SUPIII-Dist(config)#ip access-list extended VOICE 4006-SUPIII-Dist(config-ext-nacl)#remark Match the UDP ports that VoIP Uses for Bearer Traffic 4006-SUPIII-Dist(config-ext-nacl)#permit udp any any range 16384 32767 4006-SUPIII-Dist(config)#ip access-list extended VOICE-CONTROL 4006-SUPIII-Dist(config-ext-nacl)#remark Match VoIP Control Traffic 4006-SUPIII-Dist(config-ext-nacl)#remark SCCP 4006-SUPIII-Dist(config-ext-nacl)#permit tcp any any range 2000 2002 4006-SUPIII-Dist(config-ext-nacl)#remark H323 Fast Start 4006-SUPIII-Dist(config-ext-nacl)#permit tcp any any eq 1720 4006-SUPIII-Dist(config-ext-nacl)#remark H323 Slow Start 4006-SUPIII-Dist(config-ext-nacl)#permit tcp any any range 11000 11999 4006-SUPIII-Dist(config-ext-nacl)#remark H323 MGCP 4006-SUPIII-Dist(config-ext-nacl)#permit udp any any eq 2427

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Step 2

Create classes based on the ACL. 4006-SUPIII-Dist(config)#class-map match-all GOLD-DATA 4006-SUPIII-Dist(config-cmap)#description Mission Critical Traffic 4006-SUPIII-Dist(config-cmap)#match access-group name GOLD-DATA 4006-SUPIII-Dist(config)#class-map match-all VOICE 4006-SUPIII-Dist(config-cmap)#description VoIP Bearer Traffic 4006-SUPIII-Dist(config-cmap)#match access-group name VOICE 4006-SUPIII-Dist(config)#class-map match-all VOICE-CONTROL 4006-SUPIII-Dist(config-cmap)#description VoIP Control Traffic (SCCP, H225, H254, MGCP) 4006-SUPIII-Dist(config-cmap)#match access-group name VOICE-CONTROL

Configuring Service Policy Create a service policy that uses the classes for admission criteria and sets the appropriate DSCP PHB label. Step 1

Create a policy to set the DSCP PHB label/value for the classes. 4006-SUPIII-Dist(config)#policy-map DISTRIBUTION-C4006-UPLINK-IN 4006-SUPIII-Dist(config-pmap)#description Set DSCP PerHopBehavior Label for VOIP Control and Bearer Traffic 4006-SUPIII-Dist(config-pmap)#class VOICE-CONTROL 4006-SUPIII-Dist(config-pmap-c)#set ip dscp 26 4006-SUPIII-Dist(config-pmap)#class VOICE 4006-SUPIII-Dist(config-pmap-c)#set ip dscp 46 4006-SUPIII-Dist(config-pmap)#class GOLD-DATA 4006-SUPIII-Dist(config-pmap-c)#set ip dscp 18

Step 2

Apply the policy to the physical interface. 4006-SUPIII-Dist(config)#int fa 4/1 4006-SUPIII-Dist(config-if)#service-policy input DISTRIBUTION-C4006-UPLINK-IN

Configuring CoS or DSCP Trust Additionally, you need to enable the Catalyst 4000 Supervisor III to trust DSCP or CoS depending on the capabilities of the access-layer switch attached. In this example, port 3/1 is attached to a Layer 3-aware access device and can trust DSCP arriving from it. Ports 3/2 and 3/3 are attached to Layer 2 only access devices, so the switch needs to trust CoS. Step 1

Configure trust for DSCP. 4006-SUPIII-Dist(config)#int g 3/1 4006-SUPIII-Dist(config-if)#qos trust dscp

Step 2

Configure trust for CoS. 4006-SUPIII-Dist(config-if)#int 4006-SUPIII-Dist(config-if)#qos 4006-SUPIII-Dist(config-if)#int 4006-SUPIII-Dist(config-if)#qos

g 3/2 trust cos g 3/3 trust cos

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Verifying the Configuration On the Catalyst 4006 distribution-layer switch, you can verify the configuration by examining the output of the following commands: Command

Description

See

show qos map cos

Displays the QoS CoS mapping information.

Example 3-21

show policy-map interface

Displays policy mapping information.

Example 3-22

show port qos

Displays the Qos settings for a specified port.

Example 3-23

show interface counters

Displays statistics regarding traffic seen on the Example 3-24 physical interface.

Example 3-21 Displaying the QoS CoS-to-DSCP M appings 4006-SUPIII-Dist#show qos map cos CoS-DSCP Mapping Table CoS: 0 1 2 3 4 5 6 7 -------------------------------DSCP: 0 8 16 26 34 46 48 56 4006-SUPIII-Dist#show qos map dscp tx-queue DSCP-TxQueue Mapping Table (dscp = d1d2) d1 : d2 0 1 2 3 4 5 6 7 8 9 ------------------------------------0 : 01 01 01 01 01 01 01 01 01 01 1 : 01 01 01 01 01 01 02 02 02 02 2 : 02 02 02 02 02 02 02 02 02 02 3 : 02 02 03 03 03 03 03 03 03 03 4 : 03 03 03 03 03 03 03 03 04 04 5 : 04 04 04 04 04 04 04 04 04 04 6 : 04 04 04 04

Example 3-22 Displaying Policy Information 4006-SUPIII-Dist#show policy-map interface fa 4/1 service-policy input: DISTRIBUTION-C4006-UPLINK-IN class-map: GOLD-DATA (match-all) 0 packets match: access-group name GOLD-DATA set: ip dscp 18 class-map: VOICE-CONTROL (match-all) 0 packets match: access-group name VOICE-CONTROL set: ip dscp 26 class-map: VOICE (match-all) 0 packets match: access-group name VOICE set: ip dscp 46

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class-map: class-default (match-any) 0 packets match: any 0 packets

Example 3-23 Displaying QoS Queuing Information 4006-SUPIII-Dist#show qos int g 3/1 QoS is enabled globally Port QoS is enabled Port Trust State: 'dscp' Default DSCP: 0 Default CoS: 0 Tx-Queue Bandwidth ShapeRate Priority (bps) (bps) 1 250000000 disabled N/A 2 250000000 disabled N/A 3 250000000 disabled high 4 250000000 disabled N/A

QueueSize (packets) 1920 1920 1920 1920

4006-SUPIII-Dist#show qos int g 3/2 QoS is enabled globally Port QoS is enabled Port Trust State: 'cos' Default DSCP: 0 Default CoS: 0 Tx-Queue Bandwidth ShapeRate Priority (bps) (bps) 1 250000000 disabled N/A 2 250000000 disabled N/A 3 250000000 disabled high 4 250000000 disabled N/A

QueueSize (packets) 1920 1920 1920 1920

4006-SUPIII-Dist#show qos int g 3/3 QoS is enabled globally Port QoS is enabled Port Trust State: 'cos' Default DSCP: 0 Default CoS: 0 Tx-Queue Bandwidth ShapeRate Priority (bps) (bps) 1 250000000 disabled N/A 2 250000000 disabled N/A 3 250000000 disabled high 4 250000000 disabled N/A

QueueSize (packets) 1920 1920 1920 1920

Example 3-24 Displaying Traffic Statistics 4006-SUPIII-Dist#show int g3/2

count all

Port Gi3/2

InBytes 0

InUcastPkts 0

InMcastPkts 0

InBcastPkts 0

Port Gi3/2

OutBytes 0

OutUcastPkts 0

OutMcastPkts 0

OutBcastPkts 0

Port Gi3/2

InPkts 64 0

OutPkts 64 0

InPkts 65-127 0

OutPkts 65-127 0

Port Gi3/2

InPkts 128-255 0

OutPkts 128-255 0

InPkts 256-511 0

OutPkts 256-511 0

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Port Gi3/2

InPkts 512-1023 0

OutPkts 512-1023 0

Port Gi3/2

InPkts 1024-1518 OutPkts 1024-1518 InPkts 1519-1548 OutPkts 1519-1548 0 0 0 0

Port Gi3/2

InPkts 1024-1522 OutPkts 1024-1522 InPkts 1523-1548 OutPkts 1523-1548 N/A N/A N/A N/A

Port

InPkts 1549-9216 OutPkts 1549-9216

Port Gi3/2

InPkts 1549-9216 OutPkts 1549-9216 0 0

Port Gi3/2

Tx-Bytes-Queue-1 0

Tx-Bytes-Queue-2 Tx-Bytes-Queue-3 0 0

Tx-Bytes-Queue-4 0

Port Gi3/2

Tx-Drops-Queue-1 0

Tx-Drops-Queue-2 Tx-Drops-Queue-3 0 0

Tx-Drops-Queue-4 0

Port Gi3/2

Rx-No-Pkt-Buff 0

Port Gi3/2

UnsupOpcodePause 0

Port Gi3/2

RxPauseFrames 0

TxPauseFrames 0

PauseFramesDrop 0

CrcAlign-Err 0

TxCrc-Err 0

Collisions 0

Symbol-Err 0

Port Gi3/2

Undersize 0

Oversize 0

Fragments 0

Jabbers 0

Port Gi3/2

Single-Col 0

Multi-Col 0

Late-Col 0

Excess-Col 0

Port Gi3/2

Deferred-Col 0

False-Car 0

Carri-Sen 0

Sequence-Err 0

Port Gi3/2

RxIslTagFrames 0

TxIslTagFrames RxDot1qTagFrames 0 0

TxDot1qTagFrames 0

Port Gi3/2

RxMacFifoOverrun RxMacFifoUnderrun RxCdmFifoOverrun TxCsmFifoUnderrun 0 0 0 0

Port Gi3/2

NoPBA/CdmFifoOverun 0

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Catalyst 3550 as a Distribution-Layer Sw itch Figure 3-16 shows a general model for the Catalyst 3550 as a distribution device (as illustrated in the QoS configurations discussed in this chapter). Figure 3-16 General M odel for Catalyst 3550 as a Distribution Sw itch in QoS Configurations

3550

Distribution

Si

0/1

7200 WAN router

3550 0/1

0/3

0/2

Si

0/2

6500 w/ PFC

0/1 0/3

4000

3500

Access VVID=111

IP

VLAN=10

IP

VLAN=11

VVID=112 IP

VLAN=12

74707

VVID=110

For the Catalyst 3550, QoS requires the following changes to the configuration of the distribution switch: 1. Enable QoS. 2. Change the default CoS-to-DSCP mapping table so that CoS and DSCP PHB label behavior can be

maintained throughout the network. 3. Enable priority queuing (per port). Default admission to priority queue matches our requirements. 4. Configure ACLs, associate them with service policies, and apply the policy to an interface. 5. Configure CoS or DSCP trust for access Layer 2 and Layer 3 aware switches.

Enabling QoS To enable QoS on the Catalyst 3550, do the following: Step 1

Enable QoS. 3550G-Dist(config)#mls qos

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M odifying the CoS-to-DSCP M apping There are 8 CoS labels and 64 possible DSCP labels. To trust the CoS markings, the default CoS-to-DSCP mapping table must be modified to equate CoS 3 (VoIP control traffic) to AF31, CoS 5 (VoIP bearer traffic) to EF, and CoS 4 to AF41. Step 1

The default CoS-to-DSCP mapping is as follows: 3550G-Dist#show mls qos maps

Cos-dscp map: cos: 0 1 2 3 4 5 6 7 -------------------------------dscp: 0 8 16 24 32 40 48 56

Change the default CoS-to-DSCP mapping so that CoS 5 = EF and CoS 3 = AF31 and CoS 4 = AF41. 3550G-Dist(config)#mls qos map cos-dscp 0 8 16 26 34 46 48 56

Enabling Priority Queuing To enable priority queuing, do the following: Step 1

Specify the interface range. 3550G-Dist(config)#interface range g 0/1 - 12

Step 2

Specify the priority queue. 3550G-Dist(config-if-range)#priority-queue out

Step 3

Move the CoS 5 traffic to queue 4, which is the priority queue for the Catalyst 3500 family. 3550G-Dist(config-if-range)#wrr-queue cos-map 4 5

Configuring ACLs There are times when classification of traffic by the access-layer switch is required. The Catalyst 3550 has a powerful set of features that allow us to classify traffic as it enters the network. The following configuration illustrates how to classify VoIP bearer and control traffic with the Catalyst 3550 as it enters the network. Step 1

Create ACLs to identify the traffic. 3550G-Dist(config)#ip access-list extended GOLD-DATA 3550G-Dist(config-ext-nacl)#remark Match IP Address of the application server 3550G-Dist(config-ext-nacl)#permit ip any host 192.168.100.1 3550G-Dist(config-ext-nacl)#permit ip host 192.168.100.1 any 3550G-Dist(config)#ip access-list extended VOICE 3550G-Dist(config-ext-nacl)#remark Match the UDP ports that VoIP Uses for Bearer Traffic 3550G-Dist(config-ext-nacl)#permit udp any any range 16384 32767 3550G-Dist(config)#ip access-list extended VOICE-CONTROL 3550G-Dist(config-ext-nacl)#remark Match VoIP Control Traffic 3550G-Dist(config-ext-nacl)#remark SCCP

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3550G-Dist(config-ext-nacl)#permit 3550G-Dist(config-ext-nacl)#remark 3550G-Dist(config-ext-nacl)#permit 3550G-Dist(config-ext-nacl)#remark 3550G-Dist(config-ext-nacl)#permit 3550G-Dist(config-ext-nacl)#remark 3550G-Dist(config-ext-nacl)#permit

Step 2

tcp any any range 2000 2002 H323 Fast Start tcp any any eq 1720 H323 Slow Start tcp any any range 11000 11999 H323 MGCP udp any any eq 2427

Create classes that use the ACLs as admission criteria. 3550G-Dist(config)#class-map match-all VOICE 3550G-Dist(config-cmap)#description VoIP Bearer Traffic 3550G-Dist(config-cmap)#match access-group name VOICE 3550G-Dist(config)#class-map match-all GOLD-DATA 3550G-Dist(config-cmap)#description Mission Critical Traffic 3550G-Dist(config-cmap)#match access-group name GOLD-DATA 3550G-Dist(config)#class-map match-all VOICE-CONTROL 3550G-Dist(config-cmap)#description VoIP Control Traffic (SCCP, H225, H254, MGCP) 3550G-Dist(config-cmap)#match access-group name VOICE-CONTROL

Step 3

Create a policy to set the DSCP PHB label/value for the classes. 3550G-Dist(config)#policy-map DISTRIBUTION-C3550-UPLINK-IN 3550G-Dist(config-pmap)#description Set DSCP PerHopBehavior Label for VOIP Control and Bearer Traffic 3550G-Dist(config-pmap)#class VOICE-CONTROL 3550G-Dist(config-pmap-c)#set ip dscp 26 3550G-Dist(config-pmap)#class VOICE 3550G-Dist(config-pmap-c)#set ip dscp 46 3550G-Dist(config-pmap)#class GOLD-DATA 3550G-Dist(config-pmap-c)#set ip dscp 18

Step 4

Apply the policy to an interface so that traffic entering the network through this port is classified with the appropriate DSCP PHB Label EF and AF31 for VoIP Bearer, and Control respectively. 3550G-Dist(config)#int g 0/12 3550G-Distconfig-if)#service-policy input DISTRIBUTION-C3550-UPLINK-IN

Configuring CoS or DSCP Trust Additionally, you need to enable the Catalyst 3550 to trust DSCP or CoS depending on the capabilities of the access-layer switch attached. In this example, port 0/1 is attached to a Layer 3-aware access device and can trust DSCP arriving from it. Ports 0/2 and 0/3 are attached to Layer 2-only access devices, so the switch needs to trust CoS. Step 1

Configure trust for DSCP. 3550G-Dist(config)#int g0/1 3550G-Dist(config-if)#mls qos trust DSCP

Step 2

Configure trust for CoS. 3550G-Dist(config-if)#int 3550G-Dist(config-if)#mls 3550G-Dist(config-if)#int 3550G-Dist(config-if)#mls

g0/2 qos trust cos g0/3 qos trust cos

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Verifying the Configuration On the Catalyst 3550 access-layer switch, you can verify the configuration and performance during periods of high congestion by examining the output of the following commands: Command

Description

See

show mls qos maps

Displays the QoS CoS mapping information.

Example 3-25

show mls qos interface queueing

Displays the QoS queuing strategy.

Example 3-26

show policy-map interface

Displays statistics and configurations of input and output policies attached to an interface.

Example 3-27

show mls qos interface interface

Displays QoS information for the specified interface.

Example 3-28

Example 3-25 Displaying the QoS CoS- M apping Information 3550G-Dist#show mls qos maps Cos-dscp map: cos: 0 1 2 3 4 5 6 7 -------------------------------dscp: 0 8 16 26 34 46 48 56

Example 3-26 Displaying QoS Queuing Strategy 3550G-Dist#show mls qos interface queueing GigabitEthernet0/1 Ingress expedite queue: dis Egress expedite queue: ena wrr bandwidth weights: qid-weights 1 - 25 2 - 25 3 - 25 4 - 25 when expedite queue is disabled Dscp-threshold map: d1 : d2 0 1 2 3 4 5 6 7 8 9 --------------------------------------0 : 01 01 01 01 01 01 01 01 01 01 1 : 01 01 01 01 01 01 01 01 01 01 2 : 01 01 01 01 01 01 01 01 01 01 3 : 01 01 01 01 01 01 01 01 01 01 4 : 01 01 01 01 01 01 01 01 01 01 5 : 01 01 01 01 01 01 01 01 01 01 6 : 01 01 01 01 Cos-queue map: cos-qid 0 - 1 1 - 1 2 - 2 3 - 2 4 - 3 5 - 4 6 - 4 7 - 4

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Example 3-27 Displaying Policy Information 3550G-Dist#show policy-map interface GigabitEthernet0/12 service-policy input: DISTRIBUTION-C3550-UPLINK-IN class-map: VOICE-CONTROL (match-all) 0 packets, 0 bytes 5 minute offered rate 0 bps, drop rate 0 bps match: access-group name VOICE-CONTROL class-map: VOICE (match-all) 0 packets, 0 bytes 5 minute offered rate 0 bps, drop rate 0 bps match: access-group name VOICE class-map: GOLD-DATA (match-all) 0 packets, 0 bytes 5 minute offered rate 0 bps, drop rate 0 bps match: access-group name GOLD-DATA class-map: class-default (match-any) 0 packets, 0 bytes 5 minute offered rate 0 bps, drop rate 0 bps match: any 0 packets, 0 bytes 5 minute rate 0 bps

Example 3-28 Displaying QoS Information for the Interface 3550G-Dist#show mls qos int g0/1 GigabitEthernet0/1 trust state: trust dscp COS override: dis default COS: 0 DSCP Mutation Map: Default DSCP Mutation Map 3550G-Dist#show mls qos int g0/2 GigabitEthernet0/2 trust state: trust cos COS override: dis default COS: 0 DSCP Mutation Map: Default DSCP Mutation Map

3550G-Dist#show mls qos int g0/3 GigabitEthernet0/3 trust state: trust cos COS override: dis default COS: 0 DSCP Mutation Map: Default DSCP Mutation Map

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QoS in an AVVID-Enabled Campus Netw ork Summary

Summary The following general guidelines and recommendations apply when configuring a Cisco AVVID network in a campus environment: •

Multiple queues are required on all interfaces to guarantee that loss, delay, and delay variation will not affect voice, video, mission-critical data.

•

Use service policies to set the ToS and CoS classification marking for those devices that cannot set the classification and for those devices that you cannot trust.

•

Never allow PC applications to send traffic at a CoS or ToS value of 3-7. Use the ability of the access-layer switches to manipulate the IP phone’s classification and marking ability and set the appropriate trust for access-layer ports that directly support PCs.

•

Remember that QoS in the campus is not a bandwidth management issue as much as it is a buffer management issue. TX queue congestion can cause packet loss, which can adversely affect performance of applications that are sensitive to loss, delay, and delay variation.

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4

QoS in an AVVID-Enabled W ide-Area Netw ork This chapter provides information about implementing QoS in an AVVID-enabled wide-area network (WAN). It includes the following:

Note

•

Overview

•

QoS Recommendations for WAN Aggregation Routers

•

QoS Recommendations for Remote Branch Routers

•

Verifying QoS

This chapter contains references to other documents. These references are included as tips in the text. The URL for each referenced document is located in Appendix A, “Reference Information.” In some cases, an internal document is referenced. For copies of internal documents, please see your Cisco Systems representative.

Overview A fundamental principle of economics states that the more scarce a resource, the more efficiently it should be managed. In an enterprise network infrastructure, bandwidth is the prime resource and it is scarcest over the WAN. Therefore, the case for efficient bandwidth optimization via QoS technologies is strongest over the WAN, especially for enterprises that are converging their voice, video, and data networks. This chapter provides design guidance for enabling QoS over the WAN. It is important to note that the recommendations put forward in this chapter are not autonomous. They are critically dependent on the recommendations discussed in Chapter 3, “QoS in an AVVID-Enabled Campus Network.” This chapter focuses strictly on the WAN components of the Cisco AVVID Network Infrastructure (as shown in Figure 4-1), specifically the: •

WAN aggregation routers

•

Remote-branch routers

•

WAN media

For general information about using QoS for voice and video, see Chapter 1, “Overview.”

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Figure 4-1

WAN Infrastructure

IP IP Si

IP

WAN Si

IP

Distribution

Access

Si

Core

IP

WAN aggregator

IP

Branch router

Access

81031

IP

IP phones

IP

Si

IP phones

QoS Toolset The challenges of packet loss, delay, and delay variation can be addressed through the application of various QoS tools. This section provides information about the use of QoS tools in WAN environments. For general information about the QoS Toolset, see the “What is the Quality of Service Toolset?” section on page 1-12.

Classification In a WAN environment, classification is generally DSCP-based. NBAR can also be used for classification within the WAN. For information on these two tools, see the “Classification Tools” section on page 1-12.

Provisioning With respect to provisioning tools in a WAN environment, special consideration should be given to the following: •

Policers and Shapers

•

Link-Fragmentation and Interleaving

•

TX Ring

Policers and Shapers The principle drawback in strict traffic policing is that TCP will retransmit dropped packets and will throttle flows up and down, until the all the data is sent (or the connection times-out). Such TCP ramping behavior results in inefficient use of bandwidth (both over-utilizing and under-utilizing the WAN links). Because shaping usually delays packets rather than dropping them, it smooths flows and allows for more efficient use of WAN bandwidth. Therefore, shaping is more suitable in the WAN than policing. This is especially in the case with NBMA WAN media where physical access speed can vary between two endpoints, such as Frame Relay and ATM (as shown in Figure 4-2).

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Figure 4-2

Varying Access Speeds in NBM A Networks Cause Delay and Drops

Result: Buffering that will cause delay and, eventually, dropped packets 128 kbps 256 kbps Remote Sites

512 kbps 768 kbps

Frame Relay, ATM

T1

Central Site 81039

T1

Link-Fragmentation and Interleaving For slow-speed (768 kbps or below) WAN connections it is necessary to provide a mechanism for LFI. A data frame can only be sent to the physical wire at the serialization rate of the interface. This serialization rate is the size of the frame divided by the clocking speed of the interface. For example, a 1500 byte frame takes 214 ms to serialize on a 56 kbps circuit. If a delay-sensitive voice packet is behind a large data packet in the egress interface queue, the end-to-end delay budget of 150-200 msec could be exceeded. Additionally, even relatively small frames can adversely affect overall voice quality by simply increasing the delay variation to a value greater than the size of the adaptive jitter buffer at the receiver. In WANs, two tools are available for LFI: MLP LFI (for point-to-point links), and FRF.12 (for Frame Relay links).

Tip

For more information on FRF.12, see Configuring FRF.12 Fragmentation on Switched PVCs.

TX Ring On all PPP and MLP interfaces, the TX ring buffer size is automatically configured. These default buffer values can not be changed. On Frame Relay links, the TX ring is for the main interface, which all sub-interfaces use. The default value is 64 packets. This may need to be changed if the sub-interface is very small or there are many sub-interfaces. Otherwise, TX rings need to be adjusted on low-bandwidth ATM PVCs, where they should be set to a value of 3. Table 4-1 shows the default TX ring values for WAN Interfaces. Table 4-1

Default Tx Ring Values

M edia

Default TX-Ring Buffer Sizing (packets)

PPP

6

MLP

2

ATM

8192 (Must be changed for low speed VCs.)

Frame Relay

64 (per main T1 interface)

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M odular QoS Command-Line Interface The Modular QoS CLI (MQC) was developed with the objective of making QoS configuration more consistent across platforms. MQC is a syntax structure for QoS policies, consisting of three parts: •

class-map statement— classifies traffic

•

policy-map statement— defines the treatment for the various classes of traffic

•

service-policy statement—binds the policy to an interface and specifies direction

MQC offers simplicity and consistency in policy definition as its main advantages. MQC also supports the ability to define policies within policies (hierarchical policies). Hierarchical policies are essential for deploying AVVID policies on distributed Frame Relay WAN aggregators. Also, MQC has associated with it an SNMPv2 MIB (CISCO-CLASS-BASED-QOS-MIB), which provides detailed, granular visibility for QoS monitoring and management.

Tip

For more information, see Modular Quality of Service Command Line Interface in the Cisco IOS Quality of Service Solutions Configuration Guide, Release 12.2. For hierarchical policies, see the Traffic Policy as a QoS Policy (Hierarchical Traffic Policies) Example. And for the MIB, see the Cisco Class-Based QoS Configuration and Statistics MIB.

QoS Recommendations for W AN Aggregation Routers This section contains information about using QoS in WAN aggregation routers. It covers the following: •

Classifying and Provisioning for Voice on the WAN Edge

•

Classifying and Provisioning for Video on the WAN Edge

•

Classifying and Provisioning for Data on the WAN Edge

•

Link-Specific WAN QoS Recommendations

•

Summary Configurations

Classifying and Provisioning for Voice on the W AN Edge On the WAN edges (both at the WAN aggregator and the remote-branch), voice traffic needs to be assigned to an LLQ and voice control traffic needs a minimum bandwidth guarantee (CBWFQ). The bandwidth required for LLQ traffic can be expressed quantitatively (in absolute kbps) or it can be expressed relatively (as of IOS 12.2.2T) using the percent keyword. This keyword can enable increased modularity of configuration and simplification of management. Expressing the bandwidth reservation in absolute kbps or as a percentage is at the administrator's discretion.

Note

If the percent keyword is used for one LLQ provisioning, then it must be used for all other LLQ provisioning (as in the case of voice and video). Likewise, if an LLQ is provisioned in terms of absolute kbps, then any additional LLQs must also be provisioned in absolute kbps.

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Tip

For more information on the percent keyword, see Low Latency Queueing with Priority Percentage Support. In the following configuration for voice only over a T1 link: •

Voice is assigned to an LLQ.

•

Voice control traffic is guaranteed.

•

All non-voice traffic is assigned to a default queue to receive weighted-fair queueing.

class-map match-all VOICE match ip dscp ef ! class-map match-all VOICE-CONTROL match ip dscp af31 ! ! policy-map WAN-EDGE class VOICE priority percent 33 class VOICE-CONTROL bandwidth percent 2 class class-default fair-queue

Or: class-map match-all VOICE match ip dscp ef ! class-map match-all VOICE-CONTROL match ip dscp af31 ! ! policy-map WAN-EDGE class VOICE priority 506 class VOICE-CONTROL bandwidth percent 2 or bandwidth 30 class class-default fair-queue

DSCP keywords and decimal values are completely synonymous (DSCP EF is the exactly the same as DSCP 46). Both refer to a value of 101110 in the first 6 bits of the ToS byte.

Note

At the time of writing, IOS 12.2(8)T converts DSCP keywords to their decimal equivalents in the running configuration.

Note

Remember that this policy does not take effect until it is bound to an interface with a service-policy statement. Service-policy statements are discussed in the “Link-Specific WAN QoS Recommendations” section. For more information about LLQ and CBWFQ, see “Scheduling Tools” section on page 1-17.

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Classifying and Provisioning for Video on the W AN Edge On the WAN edges (both at the WAN-aggregator and the remote-branch), video conferencing traffic should to be assigned to an LLQ. The video stream minimum bandwidth guarantee should be the size of the stream plus an additional 20%. Also, the LLQ burst parameter should be set to 30000 bytes per 384 kbps stream.

Tip

Additional details on bandwidth provisioning for video conferencing are explained in the IP Videoconferencing Solution Reference Network Design Guide. In the following configuration for video only over a T1 link: •

Video conferencing traffic is assigned to an LLQ.

•

All non-video traffic is assigned to a default queue for weighted-fair queueing.

class-map match-all VIDEO match ip dscp af41 ! ! policy-map WAN-EDGE class VIDEO priority 460 30000 class class-default fair-queue

Note

Remember that this policy does not take effect until it is bound to an interface with a service-policy statement. Service-policy statements are discussed in the “Link-Specific WAN QoS Recommendations” section.

Classifying and Provisioning for Data on the W AN Edge Most enterprises have many applications that can be considered mission-critical (Gold). However, if too many applications are classified as mission-critical, they will contend amongst themselves for bandwidth and the result will be a dampening QoS effectiveness. A regular FIFO link (with no QoS) is scheduled in the exact same manner as a link where every application is provisioned as mission-critical. Therefore, it is recommended that you classify a maximum of three applications as mission-critical (Gold). Mission-critical applications should be marked with different AF drop-preference values to distinguish them from each other. These distinctions will provide more granular visibility in managing and monitoring application traffic and aid in provisioning for future requirements. Similar arguments can be made for having no more than three applications in a guaranteed-bandwidth (Silver) class of applications. You should also mark these applications with different AF drop-preference values. Default traffic is automatically marked as best effort (DSCP 0). However, non-critical bandwidth-intensive traffic could be marked differently, so that adverse policies could be applied to control such traffic. These types of traffic can be described as “less-than best-effort”, or “scavenger” traffic. For information on the recommended DSCP traffic classifications for data, see Table 1-3 on page 1-15.

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It is imperative that DSCP classification be performed on all packets prior to their arriving at the WAN edges. This allows queueing and congestion-avoidance to be performed at the WAN edge based strictly on DSCP markings, which reduces WAN aggregator CPU overhead.

Note

The default class-map match setting is match-all. Therefore, when you attempt to classify mutually-exclusive traffic flows (such as differing DSCP values), it is important to explicitly use the match-any qualifier when defining the class-map. Example 4-1 shows how four classes of traffic (gold, silver, bronze, and less-than-best-effort) can be classified into three queues. Example 4-1

Four Classes in Three Queues

ip cef For distributed platforms, use ip cef distributed. ! … ! class-map match-any GOLD-DATA match ip dscp af21 match ip dscp af22 match ip dscp af23 ! class-map match-any SILVER-DATA match ip dscp af11 match ip dscp af12 match ip dscp af13 ! policy-map WAN-EDGE class GOLD-DATA bandwidth percent 25 random-detect dscp-based class SILVER-DATA bandwidth percent 15 random-detect dscp-based class class-default fair-queue random-detect dscp-based The queue depth and thresholds are increased for the default random-detect dscp 0 96 128 10 random-detect dscp 2 70 128 10 queue. This allows more traffic and increases the portability (to random-detect dscp 4 58 128 10 random-detect dscp 6 44 128 10

Frame Relay Traffic-Shaping [FRTS] interfaces and VIP platforms) of the configuration.

The best effort traffic and the less-than-best-effort traffic (DSCP 2, 4, 6) share the default queue, but the random-detect thresholds have been adjusted such that less-than-best-effort traffic is dropped significantly sooner than regular best-effort traffic. Example 4-2 shows how four classes of traffic (gold, silver, bronze, and less-than-best-effort) can be classified into four queues.

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Example 4-2

Four-Classes in Four Queues

ip cef ! … ! class-map match-any GOLD-DATA match ip dscp af21 match ip dscp af22 match ip dscp af23 ! class-map match-any SILVER-DATA match ip dscp af11 match ip dscp af12 match ip dscp af13 ! class-map match-any