Can TCAM memory issue cause high CPU on 3750 stack?

[Omkar Tambalkar]

We have a 3750 stack with a mix of 3750G and 3750X switches. The current active template on the switch is desktop default and we are running EIGRP on the switch with large routing table so we get the TCAM error that a specific prefix cannot be programmed in TCAM memory so it will be software forwarded.

%PLATFORM_UCAST-4-PREFIX:  One or more, more specific prefixes could not be programmed into TCAM and are being covered by a less specific prefix, and the packets may be software forwarded

This error is quite frequent on a daily basis. My question is that will this error create a high CPU situation and affect traffic processing on the stack causing ESX Hosts to become unresponsive?        

[Giuseppe Larosa]

Hello Omkar,

yes TCAM full leads to high cpu usage, This may happen also on C6500/C7600

It is not the error by itself, but it is the fact that traffic with destination belonging to IPv4 prefixes not programmed in TCAM is process switched that causes spikes in cpu usage with overall performance degradation.

You have to take the time to change SDM template or to find a way to reduce the total number of routes ( using EIGRP you can perform manual summarization on a per interface basis) on the affected device(s).

Changing SDM template requires reload so you will need a maintenance time window

Hope to help

Giuseppe