Enterprise QoS Solution Reference Network Design Guide

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WAN Edge Classification and Provisioning Models 3-8 Enterprise QoS Solution Reference Network Design Guide Chapter 3 WAN Aggregator QoS Design These additional configurations are superfluous and inefficient for the router to process. The MQC implicit class-default should be used instead. Another advantage of using the MQC implicit class-default is that (currently, before Consistent QoS Behavior code) on nondistributed platforms, class-default is the only class that supports fair queuing within it. Verification command: show policy Verification Command: show policy The preceding three-class policy, like any other MQC policy, can be verified using the show policy command, as shown in Example 3-5. Example 3-5 Verification of Three-Class WAN Edge Policy RBR-2691-Right#show policy WAN-EDGE Policy Map WAN-EDGE Class VOICE Strict Priority ! Voice will get LLQ Bandwidth 33 (%) ! LLQ is provisioned to 33% compress: header ip rtp ! cRTP is enabled Class CALL-SIGNALING Bandwidth 5 (%) Max Threshold 64 (packets) ! Call-Signaling gets 5% BW Class class-default Flow based Fair Queueing ! Data will get FQ Bandwidth 0 (kbps) Max Threshold 64 (packets) RBR-2691-Right# The Five-Class WAN Edge Model builds on the previous Three-Class WAN Edge Model and includes a provision for a Critical Data class and a Scavenger class. The new Critical Data class requires Transactional Data traffic to be marked to DSCP AF21 (or AF22, in the case of dual-rate policers deployed within the campus). Additionally, IGP routing (marked by the routers as CS6) and Network-Management traffic (recommended to be marked to CS2) are protected within this class. In this example, the Critical Data class is provisioned to 36 percent of the link and DSCP-based WRED is enabled on it. The Scavenger class constrains any traffic marked to DSCP CS1 to 1 percent of the link; this allows class-default to use the remaining 25 percent. However, to constrain Scavenger to 1 percent, an explicit bandwidth guarantee (of 25 percent) must be given to the Best-Effort class. Otherwise, if class-default is not explicitly assigned a minimum bandwidth guarantee, the Scavenger class still can rob it of bandwidth. This is because of the way the CBWFQ algorithm has been coded: If classes protected with a bandwidth statement are offered more traffic than their minimum bandwidth guarantee, the algorithm tries to protect such excess traffic at the direct expense of robbing bandwidth from class-default (if class-default is configured with fair-queue), unless class-default itself has a bandwidth statement (providing itself with a minimum bandwidth guarantee). However, assigning a bandwidth statement to class-default (on nondistributed platforms) currently precludes the enabling of fair queuing (fair-queue) on this class and forces FIFO queuing on class-default (this limitation is to be removed with the release of Consistent QoS Behavior code). An additional implication of using a bandwidth statement on class-default is that even though 25 percent of the link is reserved explicitly for class-default, the parser will not attach the policy to an interface unless the max-reserved-bandwidth 100 command is entered on the interface before the Version 3.3
Chapter 3 WAN Aggregator QoS Design Version 3.3 WAN Edge Classification and Provisioning Models service-policy output statement. This is because the parser adds the sum of the bandwidth statements (regardless of whether one of these is applied to the class-default) and, if the total is in excess of 75 percent of the link’s bandwidth, rejects the application of the policy to the interface. This is shown in the following code: ! interface Multilink1 description T1 to Branch#60 ip address 10.1.112.1 255.255.255.252 max-reserved-bandwidth 100 ! overrides the default 75% BW limit service-policy output WAN-EDGE ! attaches the MQC policy ppp multilink ppp multilink group 1 ! Furthermore, WRED can be enabled on the Best-Effort class to provide congestion management. Because all traffic assigned to the default class is to be marked to the same DSCP value (of 0), it would be superfluous to enable DSCP-based WRED on such a class; WRED (technically, RED, in this case because all the [IP Precedence] weights are the same) would suffice. This Five-Class WAN Edge Model is illustrated in Figure 3-3 and detailed in Example 3-6. Figure 3-3 Five-Class WAN Edge Model Bandwidth Allocation Example Scavenger 1% Best-Effort 25% Critical Data 36% Example 3-6 Five-Class WAN Edge Model Voice 33% Call-Signaling 5% ! class-map match-all Voice match ip dscp ef ! IP Phones mark Voice to EF class-map match-any Call Signaling match ip dscp cs3 ! Future Call-Signaling marking bandwidth percent 1 ! Current Call-Signaling marking class-map match-any Critical Data match ip dscp cs6 ! Routers mark Routing traffic to CS6 match ip dscp af21 af22 ! Recommended markings for Transactional-Data match ip dscp cs2 ! Recommended marking for Network Management class-map match-all Scavenger match ip dscp cs1 ! Scavenger marking ! policy-map WAN-EDGE class Voice priority percent 33 ! Voice gets 33% of LLQ class Call Signaling bandwidth percent 5 ! BW guarantee for Call-Signaling Enterprise QoS Solution Reference Network Design Guide 3-9
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