Users Guide

• The number of interfaces in a port-pipe to which the policy-map can be applied.
Specically:
• Available CAM — the available number of CAM entries in the specied CAM partition for the specied line card or stack-unit
port-pipe.
• Estimated CAM — the estimated number of CAM entries that the policy will consume when it is applied to an interface.
• Status — indicates whether the specied 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 specied 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 rst 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)
Conguring Weights and ECN for WRED
The WRED congestion avoidance functionality drops packets to prevent buering resources from being consumed. Trac 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 buer and trac manager (BTM) (ingress or egress) can be consumed by only one or few types of trac, leaving no
space for other types. You can apply a WRED prole to a policy-map so that the specied trac can be prevented from consuming
too much of the BTM resources.
WRED drops packets when the average queue length exceeds the congured 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 congure ECN for WRED, devices employ ECN to mark the packets and reduce the rate of sending packets in a
congested network.
In a best-eort network topology, data packets are transmitted in a manner in which latency or throughput is not maintained to be at
an eective level. Packets are dropped when the network experiences a large trac load. This best-eort 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 trac state to an
optimal load. In this manner, enhanced performance and throughput are achieved. Also, the devices can respond to congestion
before a queue overows and packets are dropped, enabling improved queue management.
When a packet reaches the device with ECN enabled for WRED, the average queue size is computed. To measure the average
queue size, a weight factor is used. This weight factor is user-congurable. You can use the wred weight number command to
congure the weight for the WRED average queue size. The mark probability value is the number of packets dropped when the
average queue size reaches the maximum threshold value.
The weight factor is set to zero by default, which causes the same behavior as dropping of packets by WRED during network loads
or also called instantaneous ECN marking. In a topology in which congestion of the network varies over time, you can specify a
Quality of Service (QoS)
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