Users Guide
Specically:
• Available CAM — the available number of CAM entries in the specied CAM partition for the specied 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 specied 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 specied 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
Port-pipe | CAM Partition | Available CAM | Estimated CAM | Status
=====================================================================
0 L2ACL 500 200 Allowed(2)
Conguring Weights and ECN for WRED
The WRED congestion avoidance functionality drops packets to prevent buering resources from being consumed. Trac 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 buer
and trac manager (BTM) (ingress or egress) can be consumed by only one or few types of trac, leaving no space for other types. You
can apply a WRED prole to a policy-map so that the specied trac can be prevented from consuming too much of the BTM resources.
WRED drops packets when the average queue length exceeds the congured 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 congure
ECN for WRED, devices employ ECN to mark the packets and reduce the rate of sending packets in a congested network.
In a best-eort network topology, data packets are transmitted in a manner in which latency or throughput is not maintained to be at an
eective level. Packets are dropped when the network experiences a large trac load. This best-eort 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 trac state to an optimal
load. In this manner, enhanced performance and throughput are achieved. Also, the devices can respond to congestion before a queue
overows 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-congurable. You can use the wred weight number command to congure 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 weight to enable a
smooth, seamless averaging of packets to handle the sudden overload of packets based on the previous time sampling performed. You can
specify the weight parameter for front-end and backplane ports separately in the range of 0 through 15.
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Quality of Service (QoS)