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Cisco Bug: CSCun81101 - DFC encounters CEF exception with high tcam usage before reaching limit

Last Modified

Jul 15, 2019

Products (1)

  • Cisco Catalyst 6000 Series Switches

Known Affected Releases

15.1(1)SY2.1

Description (partial)

Symptom:
A Supervisor 2T system may experience a TCAM FIB Exception state on some linecards, even when the maximum number of routes has not been exceeded.

For example, here we see that the Supervisor has not entered an exception state, but a linecard has -

SUP2T#sh platform hardware cef exception status 
Current IPv4 FIB exception state = FALSE
Current IPv6 FIB exception state = FALSE
Current MPLS FIB exception state = FALSE
Current EoM/VPLS FIB TCAM exception state = FALSE

SUP2T#remote command mod 1 sh platform hard cef exception status detail
Current IPv4 FIB exception state = TRUE <<<<<<<<
Current IPv6 FIB exception state = FALSE
Current MPLS FIB exception state = FALSE
Current EoM/VPLS FIB TCAM exception state = FALSE

This issue can impact either IPv4 or IPv6 routes.

CPUHOG in process CFIB LC QUEUE BOOL Task is seen recurring before the exception is reported in the logs.

Feb 10 08:14:45 CET: SYS-DFC1-3-CPUHOG Task is running for (2000)msecs, more than (2000)msecs (0/0),process = CFIB LC QUEUE BOOL Task.
-Traceback= 89D4804 89D7B3C 89D8DFC 89D8FEC 89DE7D0 89DED78 89DF110 8856AE0 8856D44 8857208 8857404 88579D4 89E8948 89E8BB4 8857BE0 8857DD8
Feb 11 13:26:44 CET: SYS-DFC1-3-CPUHOG Task is running for (2000)msecs, more than (2000)msecs (0/0),process = CFIB LC QUEUE BOOL Task.
-Traceback= 89F20DC 89F2354 89F2354 89F236C 89F2354 89F236C 89F236C 89F2354 89F236C 89F236C 89D70CC 89D8FD8 89DE7D0 89DED78 89DF110 8856AE0
.
.
.
Feb 11 13:28:25 CET: SYS-DFC1-3-CPUHOG Task is running for (2000)msecs, more than (2000)msecs (2/1),process = CFIB LC QUEUE BOOL Task.
-Traceback= 89D7440 89D8DFC 89D8FEC 89DE7D0 89DED78 89DF110 8856AE0 8856D44 8857F14 8858038 8859318 884B738 88CBF50 8F92F80 8F795F4 8F7AB84
Feb 12 06:47:40 CET: CFIB-DFC1-7-CFIB_EXCEPTION FIB TCAM exception, Some entries will be software switched <<<<<<<<<

Conditions:
The cpuhog indicates that there were several times in the operation of the switch where many prefixes were being groomed.  While this is not an issue alone, it indicates routing changes in the topology.

This bug is specific to Sup2T and DFCs with the extended TCAM size (1M route capacity).  It cannot occur on the regular (nonXL modules).
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