Enterasys Networks X-Pedition XSR CLI - Manual (Page 482)

Policy-Map Commands
12-86 Configuring Quality of Service
Example
These commands create class‐map class1 and define its match criteria:
XSR(config)#class-map class1
XSR(config-cmap<class1>)#match access-group 136
These commands create the policy map which is defined to contain policy specifications for class1
and the default class:
XSR(config)#policy-map policy1
XSR(config-pmap<policy1>)#class class1
XSR(config-pmap-c<class1>)#bandwidth 2000
XSR(config-pmap-c<class1>)#queue-limit 40
XSR(config-pmap<policy1>)#class class-default
XSR(config-pmap-c<class-default>)#queue-limit 20
bandwidth
This command specifies or modify the bandwidth allocated for a class belonging to a policy map.
It is used in conjunction with a class defined by the
class-map command. The bandwidth
command specifies the bandwidth for traffic in that class. Class‐Based Weighted Fair Queueing
(CBWFQ) derives the weight for packets belonging to the class from the bandwidth allocated to
the class. CBWFQ then uses the weight to ensure that the queue for the class is serviced fairly.
The amount of bandwidth can be specified in percentages or kilobits per second (kbps). When
configured in kbps, the class weight is calculated as a ratio of the bandwidth specified for that class
over the available link bandwidth. The available link bandwidth is equal to the interface
bandwidth minus the sum of all bandwidth reserved for low latency queues. When configured in
percentages, the class weight is equal to the bandwidth percentages.
Configuring bandwidth in percentages is most useful when the underlying link bandwidth is
unknown, changes over time, or the relative class bandwidth distributions are known. For
interfaces that have adaptive shaping rates, CBWFQ can be set by configuring class bandwidths in
percentages.
The following restrictions apply to the bandwidth command:
• If the percent keyword is used, the sum of class bandwidth percentages cannot exceed 100% .
• The amount of bandwidth set should be large enough to also accommodate Layer 2 overhead.
• A policy map can have all the class bandwidths specified in kbps or all the class bandwidths
specified in percentages, but not a mix of both. But, the unit for the
priority command in the
priority class can be different from the bandwidth unit of the CBWFQ.
Syntax
bandwidth {bandwidth-kbps | percent percent}
Note: When the bandwidth of an interface is insufficient to satisfy the bandwidth of a policy map, the
interface becomes oversubscribed and some CBFWQ classes may become unable to transmit.
bandwidth-kbps Amount of bandwidth, in kbps, assigned to the class.
percent Available bandwidth percentage assigned to the class.