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Campus Distribution (Cisco Catalyst 4500) QoS Design

Chapter Description

This chapter discusses the best-practice QoS design recommendations for the Cisco Catalyst 4500 (Supervisor 6-E/7-E) series switch in the role of a campus distribution layer switch.

Queuing Models

Ingress queuing is not supported on the Catalyst 4500; only egress queuing is supported.

The Catalyst 4500 supports a strict-priority hardware queue with (up to) seven additional nonpriority hardware queues. In addition, the Catalyst 4500 supports DSCP-to-queue mapping.

At the time of this writing, DSCP-based weighted random early detection (WRED) is not supported on the Catalyst 4500 platform. However, the Catalyst 4500 family uses a platform-specific congestion avoidance algorithm to provide active queue management (AQM), namely Dynamic Buffer Limiting (DBL). DBL tracks the queue length for each traffic flow in the switch. When the queue length of a flow exceeds its limit, DBL drop packets or sets the Explicit Congestion Notification (ECN) bits in the packet headers. The DBL algorithm can identify belligerent flows (that is, unchecked/nonadaptive/inelastic flows) and drop these more aggressively. Belligerent flows can use excessive bandwidth and switch buffers, resulting in poor application performance for well-behaved flows. Therefore, DBL can induce not only random “probabilistic drops” (in a manner similar to WRED), but also “belligerent flow drops,” both of which are counted and displayed via the show policy-map interface command output on classes where DBL has been enabled (as demonstrated later in Example 15-4).

Therefore, the egress queuing model for the Catalyst 4500 platform can be expressed as 1P7Q1T+DBL.

The Catalyst 4500 can be configured to support 4-class, 8-class, or 12-class queuing models, as discussed in the following sections.

Four-Class Egress Queuing Model

In the four-class model (illustrated in Figures 11-3 and 11-4 in Chapter 11, “QoS Design Principles and Strategies”), the application class to queue mappings are as follows:

  • Real-time traffic (marked EF) is assigned to the priority queue (which may be optionally policed to 30 percent bandwidth).
  • Control traffic (marked CS3) is assigned to a dedicated nonpriority queue with a 10 percent bandwidth allocation.
  • Transactional data (marked AF2) is assigned to another dedicated nonpriority queue with a 35 percent bandwidth allocation with DBL enabled.
  • Best-effort traffic (marked DF) is assigned to a default queue with 25 percent bandwidth allocation with DBL enabled.

Figure 15-3 illustrates the resulting four-class (1P3Q1T+DBL) egress queuing model for the Catalyst 4500.

Figure 15-3

Figure 15-3 Catalyst 4500 Four-Class Egress Queuing Model

Example 15-1 shows the corresponding configuration for four-class (1P3Q1T+DBL) egress queuing on the Catalyst 4500.

Example 15-1 Four-Class (1P3Q1T+DBL) Egress Queuing Configuration Example on a Catalyst 4500

 ! This section configures the class maps for the egress queuing policy
C4500(config)# class-map match-all PRIORITY-QUEUE
C4500(config-cmap)# match dscp ef
 ! VoIP (EF) is mapped to the PQ
C4500(config)# class-map match-all CONTROL-QUEUE
C4500(config-cmap)# match dscp cs3
 ! Signaling (CS3) is mapped to a dedicated queue
C4500(config)# class-map match-all TRANSACTIONAL-DATA-QUEUE
C4500(config-cmap)# match dscp af21 af22 af23
 ! Transactional Data (AF2) is mapped to a dedicated queue


 ! This section configures the four-class egress queuing policy map
C4500(config)# policy-map 1P3Q1T
C4500(config-pmap-c)# class PRIORITY-QUEUE
C4500(config-pmap-c)#  priority
 ! Enables the priority queue
C4500(config-pmap-c)# class CONTROL-QUEUE
C4500(config-pmap-c)#  bandwidth remaining percent 10
 ! Defines the control queue with 10% BW remaining
C4500(config-pmap-c)# class TRANSACTIONAL-DATA-QUEUE
C4500(config-pmap-c)#  bandwidth remaining percent 35
C4500(config-pmap-c)#  dbl
 ! Defines a transactional data queue with 35% BW remaining + DBL
C4500(config-pmap-c)# class class-default
C4500(config-pmap-c)#  bandwidth remaining percent 25
C4500(config-pmap-c)#  dbl
 ! Provisions the default/Best Effort queue with 25% BW remaining + DBL


 ! This section attaches the egress queuing policy to the interface(s)
C4500(config)# interface range TenGigabitEthernet 1/1-2
C4500(config-if-range)# service-policy output 1P3Q1T

You can verify the configuration in Example 15-1 with the following commands:

  • show class-map
  • show policy-map
  • show policy-map interface

Eight-Class Egress Queuing Model

In the eight-class model (illustrated in Figures 11-5 and 11-6), the application class to queue mappings are as follows:

  • Real-time traffic (marked EF) is assigned to the priority queue (which may be optionally policed to 10 percent bandwidth).
  • Interactive video (marked AF4) is assigned to a dedicated nonpriority queue with a 23 percent bandwidth allocation with DBL enabled.
  • Streaming video (marked AF3) is assigned to a dedicated nonpriority queue with a 10 percent bandwidth allocation with DBL enabled.
  • Network control traffic (marked CS6) is assigned to a dedicated nonpriority queue with a 5 percent bandwidth allocation.
  • Signaling traffic (marked CS3) is assigned to a dedicated nonpriority queue with a 2 percent bandwidth allocation.
  • Transactional data (marked AF2) is assigned to dedicated nonpriority queue with a 24 percent bandwidth allocation with DBL enabled.
  • Scavenger traffic (marked CS1) is constrained within a dedicated nonpriority queue with a 1 percent bandwidth allocation.
  • Best-effort traffic (marked DF) is assigned to a default queue with 25 percent bandwidth allocation with DBL enabled.

Figure 15-4 illustrates the resulting eight-class (1P7Q1T+DBL) egress queuing model for the Catalyst 4500.

Figure 15-4

Figure 15-4 Catalyst 4500 Eight-Class (1P7Q1T+DBL) Egress Queuing Model

Example 15-2 shows the corresponding configuration for eight-class (1P7Q1T+DBL) egress queuing on the Catalyst 4500.

Example 15-2 Eight-Class (1P7Q1T+DBL) Egress Queuing Configuration Example on a Catalyst 4500

 ! This section configures the class maps for the egress queuing policy
C4500(config)# class-map match-all PRIORITY-QUEUE
C4500(config-cmap)# match dscp ef
 ! VoIP (EF) is mapped to the PQ
C4500(config)# class-map match-all INTERACTIVE-VIDEO-QUEUE
C4500(config-cmap)# match dscp af41 af42 af43
 ! Interactive-Video (AF4) is assigned a dedicated queue
C4500(config)# class-map match-all STREAMING-VIDEO-QUEUE
C4500(config-cmap)# match dscp af31 af32 af33
 ! Streaming-Video (AF3) is assigned a dedicated queue
C4500(config)# class-map match-all CONTROL-QUEUE
C4500(config-cmap)# match dscp cs6
 ! Network Control (CS6) is mapped to a dedicated queue
C4500(config)# class-map match-all SIGNALING-QUEUE
C4500(config-cmap)# match dscp cs3
 ! Signaling (CS3) is mapped to a dedicated queue
C4500(config)# class-map match-all TRANSACTIONAL-DATA-QUEUE
C4500(config-cmap)# match dscp af21 af22 af23
 ! Transactional Data (AF2) is assigned a dedicated queue
C4500(config)# class-map match-all SCAVENGER-QUEUE
C4500(config-cmap)# match dscp cs1
 ! Scavenger (CS1) is assigned a dedicated queue

 ! This section configures the 1P7Q1T+DBL egress queuing policy map
C4500(config)# policy-map 1P7Q1T
C4500(config-pmap-c)# class PRIORITY-QUEUE
C4500(config-pmap-c)#  priority
 ! Defines a priority queue
C4500(config-pmap-c)# class INTERACTIVE-VIDEO-QUEUE
C4500(config-pmap-c)#  bandwidth remaining percent 23
C4500(config-pmap-c)#  dbl
 ! Defines a interactive-video queue with 23% BW remaining + DBL
C4500(config-pmap-c)# class STREAMING-VIDEO-QUEUE
C4500(config-pmap-c)# bandwidth remaining percent 10
C4500(config-pmap-c)#  dbl
 ! Defines a streaming-video queue with 10% BW remaining + DBL
C4500(config-pmap-c)# class CONTROL-QUEUE
C4500(config-pmap-c)#  bandwidth remaining percent 5
 ! Defines a control/management queue with 5% BW remaining
C4500(config-pmap-c)# class SIGNALING-QUEUE
C4500(config-pmap-c)#  bandwidth remaining percent 2
 ! Defines a signaling queue with 2% BW remaining
C4500(config-pmap-c)# class TRANSACTIONAL-DATA-QUEUE
C4500(config-pmap-c)#  bandwidth remaining percent 24
C4500(config-pmap-c)#  dbl
 ! Defines a transactional data queue with 24% BW remaining + DBL
C4500(config-pmap-c)# class SCAVENGER-QUEUE
C4500(config-pmap-c)#  bandwidth remaining percent 1
 ! Defines a (minimal) scavenger queue with 1% BW remaining/limit
C4500(config-pmap-c)# class class-default
C4500(config-pmap-c)#  bandwidth remaining percent 25
C4500(config-pmap-c)#  dbl
 ! Provisions the default/Best Effort queue with 25% BW remaining + DBL


 ! This section attaches the egress queuing policy to the interface(s)
C4500(config)# interface range TenGigabitEthernet 1/1-2
C4500(config-if-range)# service-policy output 1P7Q1T

You can verify the configuration in Example 15-2 with the following commands:

  • show class-map
  • show policy-map
  • show policy-map interface

Twelve-Class Egress Queuing Model

In the 12-class model (illustrated in Figures 11-7 and 11-8), the application class to queue mappings are as follows:

  • Voice (marked EF), broadcast video (marked CS5), and real-time interactive traffic (marked CS4) is all assigned to the priority queue (which may be optionally policed to 30 percent bandwidth).
  • Multimedia-conferencing traffic (marked AF4) is assigned to a dedicated nonpriority queue with a 10 percent bandwidth allocation with DBL enabled.
  • Multimedia-streaming traffic (marked AF3) is assigned to a dedicated nonpriority queue with a 10 percent bandwidth allocation with DBL enabled.
  • Network control traffic (marked CS6), signaling traffic (marked CS3) and network management traffic (marked CS2) is all assigned to a dedicated nonpriority queue with a 10 percent bandwidth allocation; optionally, CS7 traffic may also be mapped to this queue.
  • Transactional data traffic (marked AF2) is assigned to dedicated nonpriority queue with a 10 percent bandwidth allocation with DBL enabled.
  • Bulk data traffic (marked AF1) is assigned to a dedicated nonpriority queue with 4 percent bandwidth allocation with DBL enabled.
  • Scavenger traffic (marked CS1) is constrained within a dedicated nonpriority queue with a 1 percent bandwidth allocation.
  • Best-effort traffic (marked DF) is assigned to a default queue with 25 percent bandwidth allocation with DBL enabled.

Figure 15-5 illustrates the resulting 12-class (1P7Q1T+DBL) egress queuing model for the Catalyst 4500.

Figure 15-5

Figure 15-5 Catalyst 4500 12-Class (1P7Q1T+DBL) Egress Queuing Model

Example 15-3 shows the corresponding configuration for 12-class (1P7Q1T+DBL) egress queuing on the Catalyst 4500.

Example 15-3 Twelve-Class (1P7Q1T+DBL) Egress Queuing Configuration Example on a Catalyst 4500

 ! This section configures the class maps for the egress queuing policy
C4500(config)# class-map match-any PRIORITY-QUEUE
C4500(config-cmap)# match dscp ef
C4500(config-cmap)# match dscp cs5
C4500(config-cmap)# match dscp cs4
 ! VoIP (EF), Broadcast Video (CS5) and Realtime Interactive (CS4)
 ! are all mapped to the PQ
C4500(config)# class-map match-any CONTROL-MGMT-QUEUE
C4500(config-cmap)# match dscp cs7
C4500(config-cmap)# match dscp cs6
C4500(config-cmap)# match dscp cs3
C4500(config-cmap)# match dscp cs2
 ! Network Control (CS7), Internetwork Control (CS6),
 ! Signaling (CS3) and Management (CS2) are mapped
 ! to a Control/Management Queue
C4500(config)# class-map match-all MULTIMEDIA-CONFERENCING-QUEUE
C4500(config-cmap)# match dscp af41 af42 af43
 ! Multimedia Conferencing (AF4) is assigned a dedicated queue
C4500(config)# class-map match-all MULTIMEDIA-STREAMING-QUEUE
C4500(config-cmap)# match dscp af31 af32 af33
 ! Multimedia Streaming (AF3) is assigned a dedicated queue
C4500(config)# class-map match-all TRANSACTIONAL-DATA-QUEUE
C4500(config-cmap)# match dscp af21 af22 af23
 ! Transactional Data (AF2) is assigned a dedicated queue
C4500(config)# class-map match-all BULK-DATA-QUEUE
C4500(config-cmap)# match dscp af11 af12 af13
 ! Bulk Data (AF1) is assigned a dedicated queue
C4500(config)# class-map match-all SCAVENGER-QUEUE
C4500(config-cmap)# match dscp cs1
 ! Scavenger (CS1) is assigned a dedicated queue


 ! This section configures the 1P7Q1T+DBL egress queuing policy map
C4500(config)# policy-map 1P7Q1T
C4500(config-pmap-c)# class PRIORITY-QUEUE
C4500(config-pmap-c)#  priority
 ! Defines a priority queue
C4500(config-pmap-c)# class CONTROL-MGMT-QUEUE
C4500(config-pmap-c)#  bandwidth remaining percent 10
 ! Defines a control/management queue with 10% BW remaining
C4500(config-pmap-c)# class MULTIMEDIA-CONFERENCING-QUEUE
C4500(config-pmap-c)#  bandwidth remaining percent 10
C4500(config-pmap-c)#  dbl
 ! Defines a multimedia conferencing queue with 10% BW remaining + DBL
C4500(config-pmap-c)# class MULTIMEDIA-STREAMING-QUEUE
C4500(config-pmap-c)#  bandwidth remaining percent 10
C4500(config-pmap-c)#  dbl
 ! Defines a multimedia streaming queue with 10% BW remaining + DBL
C4500(config-pmap-c)# class TRANSACTIONAL-DATA-QUEUE
C4500(config-pmap-c)#  bandwidth remaining percent 10
C4500(config-pmap-c)#  dbl
 ! Defines a transactional data queue with 10% BW remaining + DBL
C4500(config-pmap-c)# class BULK-DATA-QUEUE
C4500(config-pmap-c)#  bandwidth remaining percent 4
C4500(config-pmap-c)#  dbl
 ! Defines a bulk data queue with 10% BW remaining + DBL
C4500(config-pmap-c)# class SCAVENGER-QUEUE
C4500(config-pmap-c)#  bandwidth remaining percent 1
 ! Defines a (minimal) scavenger queue with 1% BW remaining/limit
C4500(config-pmap-c)# class class-default
C4500(config-pmap-c)#  bandwidth remaining percent 25
C4500(config-pmap-c)#  dbl
 ! Provisions the default/Best Effort queue with 25% BW remaining + DBL


 ! This section attaches the egress queuing policy to the interface(s)
C4500(config)# interface range TenGigabitEthernet 1/1-2
C4500(config-if-range)# service-policy output 1P7Q1T

You can verify the configuration in Example 15-3 with the following commands:

  • show class-map
  • show policy-map
  • show policy-map interface (as shown in Example 15-4)

Example 15-4 Verifying Queuing Policies on a Catalyst 4500: show policy-map interface

C4500# show policy-map interface TenGigabitEthernet 1/1
 TenGigabitEthernet1/1
  Service-policy output: 1P7Q1T

    Class-map: PRIORITY-QUEUE (match-any)
      102598 packets
      Match:  dscp ef (46)
        102598 packets
      Match:  dscp cs5 (40)
        0 packets
      Match:  dscp cs4 (32)
        0 packets
      priority queue:
          Transmit: 22782306 Bytes, Queue Full Drops: 0 Packets

    Class-map: CONTROL-MGMT-QUEUE (match-any)
      24847 packets
      Match:  dscp cs7 (56)
        0 packets
      Match:  dscp cs6 (48)
        0 packets
      Match:  dscp cs3 (24)
        24847 packets
      Match:  dscp cs2 (16)
        0 packets
      bandwidth remaining 10 (%)
          Transmit: 24909844 Bytes, Queue Full Drops: 0 Packets


    Class-map: MULTIMEDIA-CONFERENCING-QUEUE (match-all)
      22280511 packets
      Match:  dscp af41 (34) af42 (36) af43 (38)
      bandwidth remaining 10 (%)
          Transmit: 4002626800 Bytes, Queue Full Drops: 0 Packets
      dbl
          Probabilistic Drops: 0 Packets
          Belligerent Flow Drops: 0 Packets


    Class-map: MULTIMEDIA-STREAMING-QUEUE (match-all)
      0 packets
      Match:  dscp af31 (26) af32 (28) af33 (30)
      bandwidth remaining 10 (%)
          Transmit: 0 Bytes, Queue Full Drops: 0 Packets
      dbl
          Probabilistic Drops: 0 Packets
          Belligerent Flow Drops: 0 Packets


    Class-map: TRANSACTIONAL-DATA-QUEUE (match-all)
      235852 packets
      Match:  dscp af21 (18) af22 (20) af23 (22)
      bandwidth remaining 10 (%)
          Transmit: 247591260 Bytes, Queue Full Drops: 0 Packets
      dbl
          Probabilistic Drops: 0 Packets
          Belligerent Flow Drops: 0 Packets


    Class-map: BULK-DATA-QUEUE (match-all)
      2359020 packets
      Match:  dscp af11 (10) af12 (12) af13 (14)
      bandwidth remaining 4 (%)
          Transmit: 2476460700 Bytes, Queue Full Drops: 0 Packets
      dbl
          Probabilistic Drops: 0 Packets
          Belligerent Flow Drops: 0 Packets


    Class-map: SCAVENGER-QUEUE (match-all)
      78607323 packets
      Match:  dscp cs1 (8)
      bandwidth remaining 1 (%)
          Transmit: 98144078642 Bytes, Queue Full Drops: 26268 Packets


    Class-map: class-default (match-any)
      12388183 packets
      Match: any
        12388183 packets
      bandwidth remaining 25 (%)
          Transmit: 13001465825 Bytes, Queue Full Drops: 0 Packets
      dbl
          Probabilistic Drops: 0 Packets
          Belligerent Flow Drops: 0 Packets
C4500#

Example 15-4 shows various queuing classes and their associated packet and byte counts, including 26,268 queuing drops noted on the scavenger queue.

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