CANOGA PERKINS 9175 Configuration Guide - Manual (Page 210)

CanogaOS Configuration Guide
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drops more packets from large users than small. Therefore, sources that generate the
most traffic are more likely to be slowed down versus sources that generate little traffic.
You can enable WRED and configure the two thresholds for a drop-precedence
assigned to every egress queues. The WRED’s color drop precedence map is the same
as tail-drop’s. Each min-threshold represents where WRED starts to randomly drop
packets. After min-threshold is exceeded, WRED randomly begins to drop packets
assigned to this threshold. As the queue max-threshold is approached, WRED continues
to drop packets randomly with the rate of drop-probability. When the max-threshold is
reached, WRED drops all packets assigned to the threshold. By default, WRED is
disabled.
Scheduling
Scheduling forwards conditions packets using combination of WDRR and SP. Every
queue belongs to a class. The class rang from 0 to 3, and 3 is the highest priority.
Several queues can be in a same class, or non queue in some class. Packets are
scheduled by SP between classes and WDRR between queues in a class.
• Strict Priority-Based (SP), in which any high-priority packets are first transmitted.
Lower-priority packets are transmitted only when the higher-priority queues are
empty. A problem may occur when too many lower-priority packets are not
transmitted.
• Weighted Deficit Round Robin (WDRR), in which each queue is assigned a
weight to control the number of packets relatively sent from each queue.
Class Map
A class map names and isolates specific traffic from other traffic. The class map defines
the criteria used to match against a specific traffic flow to further classify it. The criteria
can match several access groups defined by the ACL.
If there is more than one type of traffic to be classified, another class map can be created
under a different name. After a packet is matched against the class-map criteria, it is
further classified using a policy map.
Policy Map
A policy map specifies on which traffic class to act. This can be implemented as follows:
• Set a specific priority and color in the traffic class.
• Set a specific trust policy to map priority and color.
• Specify the traffic bandwidth limitations for each matched traffic class (policer)
and the action to take (marking) when the traffic is out of profile.
Policy maps have the following attributes:
• A policy map can contain multiple class statements, each with different match
criteria and action.
• A separate policy-map class can exist for each type of traffic received through an
interface.
• There can be only one policy map per interface per direction. The same policy
map can be applied to multiple interfaces and directions.
• Before a policy map can be effective, it must be attached to an interface.