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Cisco Bug: CSCuq33385 - 3850 Switch Leaks Flow Manager Entries due to UDP

Last Modified

Jun 09, 2017

Products (1)

  • Cisco IOS

Known Affected Releases

15.0(1)EZ3

Description (partial)

Symptom:
A 3850 switch may see leaks in the flow manager table, leading to an eventual crash if an IOS process attempts to obtain a flow entry but cannot. A common victim process that can see this issue is IP SLA. Eg:

*Jul 28 17:30:41.790: %SYS-3-CPUHOG: Task is running for (158390)msecs, more than (2000)msecs (2/2),process = IP SLAs XOS Event Processor.
-Traceback= XXXXXXXX ...

Conditions:
UDP packets are being processed by the flow manager. Netflow does not need to be explicitly configured to hit this issue. This can be seen in any context where the switch is processing UDP packets destined for itself. One way to validate this bug is being hit is to do the following:

switch#(config) service internal
switch#(config) exit

switch#show flowmgr | count udp
Number of lines which match regexp = 24

switch#show flowmgr | count udp
Number of lines which match regexp = 25

switch#show flowmgr | count udp
Number of lines which match regexp = 26

If you wait about 5-10 minute between iterations of "show flowmgr | count udp", you should continue to see a steady increase in flow manager entries due to UDP if you're hitting this bug. If the flow manager table grows to about 48k entries in total, you pose a risk of a crash or other unexpected behaviors.

This issue is seen in IOS-XE 3.3.3SE, but not 3.6.0E.
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