Enterprise QoS Solution Reference Network Design Guide

WAN Edge Classification and Provisioning Models
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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