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Dell EMC Configuration Guide for the S3100 Series 9.14.2.4

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Pre-Calculating Available QoS CAM Space

Before Dell EMC Networking OS 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 (TeGi 12/20) entries on portpipe 1

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 {stack-unit } number port-set number
  • test cam-usage service-policy input policy-map {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.
Verify that there are enough available CAM entries.
test cam-usage

Example of the test cam-usage Command

DellEMC# 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)

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