Administrator Guide

• Estimated CAM — the estimated number of CAM entries that the policy will consume when it is
applied to an interface.
• Status — indicates whether the specified policy-map can be completely applied to an interface in the
port-pipe.
– Allowed — indicates that the policy-map can be applied because the estimated number of CAM
entries is less or equal to the available number of CAM entries. The number of interfaces in the
port-pipe to which the policy-map can be applied is given in parentheses.
– Exception — indicates that the number of CAM entries required to write the policy-map to the
CAM is greater than the number of available CAM entries, and therefore the policy-map cannot be
applied to an interface in the specified port-pipe.
NOTE: The show cam-usage command provides much of the same information as the test cam-
usage command, but whether a policy-map can be successfully applied to an interface cannot be
determined without first measuring how many CAM entries the policy-map would consume; the
test cam-usage command is useful because it provides this measurement.
• Verify that there are enough available CAM entries.
test cam-usage
Example of the test cam-usage Command
Dell# test cam-usage service-policy input pmap_l2 port-set 0
Port-pipe | CAM Partition | Available CAM | Estimated CAM | Status
=====================================================================
0 L2ACL 500 200 Allowed(2)
Configuring Weights and ECN for WRED
The feature to configure a weight for WRED and ECN functionality for backplane ports is supported on
the Z9000 platform.
The WRED congestion avoidance functionality drops packets to prevent buffering resources from being
consumed. Traffic is a mixture of various kinds of packets. The rate at which some types of packets arrive
might be greater than others. In this case, the space on the buffer and traffic manager (BTM) (ingress or
egress) can be consumed by only one or few types of traffic, leaving no space for other types. You can
apply a WRED profile to a policy-map so that the specified traffic can be prevented from consuming too
much of the BTM resources.
WRED drops packets when the average queue length exceeds the configured threshold value to signify
congestion. ECN is a capability that enhances WRED by marking the packets instead of causing WRED to
drop them when the threshold value is exceeded. If you configure ECN for WRED, devices employ ECN
to mark the packets and reduce the rate of sending packets in a congested network.
In a best-effort network topology, data packets are transmitted in a manner in which latency or
throughput is not maintained to be at an effective level. Packets are dropped when the network
experiences a large traffic load. This best-effort network deployment is not suitable for applications that
are time-sensitive, such as video on demand (VoD) or voice over IP (VoIP) applications. In such cases, you
can use ECN in conjunction with WRED to resolve the dropping of packets under congested conditions.
Using ECN, the packets are marked for transmission at a later time after the network recovers from the
heavy traffic state to an optimal load. In this manner, enhanced performance and throughput are
Quality of Service (QoS)
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