Reference Guide

FTOS#
Pre-Calculating Available QoS CAM Space
Pre-calculating available QoS CAM space is supported on the S4820T platform.
Before FTOS version 7.3.1, there was no way to measure the number of CAM entries a policy-map would consume (the
number of CAM entries that a rule uses is not predictable; from 1 to 16 entries might be used per rule depending upon its
complexity). Therefore, it was possible to apply to an interface a policy-map that requires more entries than are
available. In this case, the system writes as many entries as possible, and then generates an CAM-full error message
(shown in the following example). The partial policy-map configuration might cause unintentional system behavior.
%EX2YD:12 %DIFFSERV-2-DSA_QOS_CAM_INSTALL_FAILED: Not enough space in L3
Cam(PolicyQos) for class 2 (Gi 12/20) entries on portpipe 1 for linecard 12
%EX2YD:12 %DIFFSERV-2-
DSA_QOS_CAM_INSTALL_FAILED: Not enough space in L3 Cam(PolicyQos) for
class 5 (Gi 12/
22) entries on portpipe 1 for linecard 12
The test cam-usage command allows you to verify that there are enough available CAM entries before applying a
policy-map to an interface so that you avoid exceeding the QoS CAM space and partial configurations. This command
measures the size of the specified policy-map and compares it to the available CAM space in a partition for a specified
port-pipe.
Test the policy-map size against the CAM space for a specific port-pipe or all port-pipes using these commands:
• test cam-usage service-policy input policy-map {linecard | stack-unit }
number port-set number
• test cam-usage service-policy input policy-map {linecard | stack-unit }
all
The output of this command, shown in the following example, displays:
• The estimated number of CAM entries the policy-map will consume.
• Whether or not the policy-map can be applied.
• The number of interfaces in a port-pipe to which the policy-map can be applied.
Specifically:
• Available CAM — the available number of CAM entries in the specified CAM partition for the specified 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 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.
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