Enterprise QoS Solution Reference Network Design Guide
Enterprise QoS Solution Reference Network Design Guide
Enterprise QoS Solution Reference Network Design Guide
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
WAN Edge Classification and Provisioning Models<br />
3-8<br />
<strong>Enterprise</strong> <strong>QoS</strong> <strong>Solution</strong> <strong>Reference</strong> <strong>Network</strong> <strong>Design</strong> <strong>Guide</strong><br />
Chapter 3 WAN Aggregator <strong>QoS</strong> <strong>Design</strong><br />
These additional configurations are superfluous and inefficient for the router to process. The MQC<br />
implicit class-default should be used instead.<br />
Another advantage of using the MQC implicit class-default is that (currently, before Consistent <strong>QoS</strong><br />
Behavior code) on nondistributed platforms, class-default is the only class that supports fair queuing<br />
within it.<br />
Verification command:<br />
show policy<br />
Verification Command: show policy<br />
The preceding three-class policy, like any other MQC policy, can be verified using the show policy<br />
command, as shown in Example 3-5.<br />
Example 3-5 Verification of Three-Class WAN Edge Policy<br />
RBR-2691-Right#show policy WAN-EDGE<br />
Policy Map WAN-EDGE<br />
Class VOICE<br />
Strict Priority ! Voice will get LLQ<br />
Bandwidth 33 (%) ! LLQ is provisioned to 33%<br />
compress:<br />
header ip rtp ! cRTP is enabled<br />
Class CALL-SIGNALING<br />
Bandwidth 5 (%) Max Threshold 64 (packets) ! Call-Signaling gets 5% BW<br />
Class class-default<br />
Flow based Fair Queueing ! Data will get FQ<br />
Bandwidth 0 (kbps) Max Threshold 64 (packets)<br />
RBR-2691-Right#<br />
The Five-Class WAN Edge Model builds on the previous Three-Class WAN Edge Model and includes a<br />
provision for a Critical Data class and a Scavenger class.<br />
The new Critical Data class requires Transactional Data traffic to be marked to DSCP AF21 (or AF22,<br />
in the case of dual-rate policers deployed within the campus). Additionally, IGP routing (marked by the<br />
routers as CS6) and <strong>Network</strong>-Management traffic (recommended to be marked to CS2) are protected<br />
within this class. In this example, the Critical Data class is provisioned to 36 percent of the link and<br />
DSCP-based WRED is enabled on it.<br />
The Scavenger class constrains any traffic marked to DSCP CS1 to 1 percent of the link; this allows<br />
class-default to use the remaining 25 percent. However, to constrain Scavenger to 1 percent, an explicit<br />
bandwidth guarantee (of 25 percent) must be given to the Best-Effort class. Otherwise, if class-default<br />
is not explicitly assigned a minimum bandwidth guarantee, the Scavenger class still can rob it of<br />
bandwidth. This is because of the way the CBWFQ algorithm has been coded: If classes protected with<br />
a bandwidth statement are offered more traffic than their minimum bandwidth guarantee, the algorithm<br />
tries to protect such excess traffic at the direct expense of robbing bandwidth from class-default (if<br />
class-default is configured with fair-queue), unless class-default itself has a bandwidth statement<br />
(providing itself with a minimum bandwidth guarantee). However, assigning a bandwidth statement to<br />
class-default (on nondistributed platforms) currently precludes the enabling of fair queuing (fair-queue)<br />
on this class and forces FIFO queuing on class-default (this limitation is to be removed with the release<br />
of Consistent <strong>QoS</strong> Behavior code).<br />
An additional implication of using a bandwidth statement on class-default is that even though 25<br />
percent of the link is reserved explicitly for class-default, the parser will not attach the policy to an<br />
interface unless the max-reserved-bandwidth 100 command is entered on the interface before the<br />
Version 3.3