HTTP monitor fails under heavy loads but connections still work for client connections

sorry for the delay in getting back to you - I appear to have just (40 mins ago) resolved the issue, now trying to figure out why!

 

I was working with F5 support who advised:

 

 

 

Another thing that would be helpful to see is if the LTM is actually getting the monitor traffic back to itself. What would be helpful is to capture a tcpdump showing when the monitors are failing during your load test.

 

tcpdump -s0 -ni internal host and host -w /var/tmp/C5XXXX-monitorcapture.dmp

 

Please use the selfIP of the LTM and not the floating IP since monitors are sent from the SelfIP of the LTM and not the floater.

 

 

As this is a test device is was setup as a single device not a pair, so to be able to just capture the monitor traffic per the above I set it up as if it was in a pair, and added a floating IP on the inside. Since then I've run two load tests and the F5 has not see the monitor fail even once, even when I dropped it back from a 15sec interval/46 sec timeout (which had failed), back to a standard 5sec internal/16 sec timeout.

 

 

The only thing in my head that could cause this would be exhausting the IP stack when on a single IP, however I don't believe this to be the case.

 

 

If anyone has any ideas I'm all ears....just glad it appears to be fixed!