Enterasys Networks X-PeditionTM manual Configuring Cbwfq, Measuring Bandwidth Utilization

Mechanisms Providing QoS

Configuring CBWFQ

CBWFQ is configured using the bandwidth command. It provides a minimum bandwidth guarantee during congestion. For example, policy-map keyser guarantees 30 percent of the bandwidth to class sosay and 60 percent of the bandwidth to class intrigue. If one class uses less of the requested share of bandwidth, the excess bandwidth may be used by the other class.

XSR(config)#policy-map keyser

XSR(config-pmap<keyser>)#class sosay

XSR(config-pmap-c<sosay>)#bandwidth percent 30

XSR(config-pmap<keyser>)#class intrigue

XSR(config-pmap-c<intrigue>)#bandwidth percent 60

Measuring Bandwidth Utilization

A quick and easy way to monitor bandwidth utilization is as follows: define an empty policy map, apply the policy to the serial sub-interface, and display the output of show policy-map. Enter the following commands:

XSR(config)#policy-map test

XSR(config-pmap<test>)#interface serial 1/1:0

XSR(config-subif<S1/1.0>)#service-policy output test

XSR(config-subif<S1/1.0>)#exit

XSR(config)#show policy-map interface serial 1/0:0

Describing Priority Queues

Priority Queues (PQ) extend absolute (strict) priority to certain traffic. Higher priority packets are sent before lower priority packets, and lower priority packets are sent before any non-priority packets. Priority queuing ensures that applications which cannot tolerate much delay (e.g., voice and video traffic) are serviced before non-time critical applications (e.g., FTP).

Traffic assigned to priority queues is rate-limited so the queue’s presence would not “starve” low priority packets and fair queues. The XSR supports up to four priority queues per interface, labeled high, medium, low, and normal. They are characterized by the following rules:

•High priority queues are emptied before low priority queues.

•PQ bandwidth is controlled using a traffic policer to rate-limit it

Note: If priority queues are configured to take up almost the entire bandwidth of the interface or PVC, CBWFQ and control packets will get no actual bandwidth and may be blocked.

Configuring Priority Queues

The priority command configures priority queuing for certain packets based on the traffic class. When you specify priority (using the following commands) for a class, it takes a bandwidth argument affording maximum bandwidth. The following commands configure priority queuing:

•policy-map policy-name

•class class-name

•priority priority-level kbps [burst-size]

Be aware that bandwidth guarantees come into play when an interface is congested, at which time traffic class guarantees bandwidth equal to the specified rate. The priority command implements a maximum bandwidth guarantee. If the priority class does not use its bandwidth, the

XSR User’s Guide 12-5