exception no http response recieved (possible connection failure)

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We have a php script that contacts google and checks user status. The problem is it fails periododicly on average fails 5 times out of 5000 users. The times it fails is spratic.The machine it runs on is behind an f5 load balancer. When we run the program on a server that is not behind the load balancer  we get no errors. I have run tcpdumps on the f5 and each machine involved but find nothing unusual. there was a tcp dup ack but i don't think thats all that unusual. Sence this is an ssl connection I can't tell exactly what the set of packets are that are causing the error.  I'm at a loss as to what to check from here. I was hoping someone would have some ideas on what to check.
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At time of failure does the F5 have any log entries.  What version of the F5 OS are you running?
- Netork Path: What are the differences in network path of access through F5 and not through F5?  See any errors there?
is the ASM enabled on the F5?

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Commented:
nothing in the logs on the f5. F5 version: BIG-IP 9.1.3 Build 37.0. network path is switch > f5 > switch> main router. The network path for non f5 is switch > main router. I don't know if asm is enabled on the f5. We also ran some interal external tcpdumps on the f5 and found no differences in the incoming and outgoing traffic. f5 engineers ran a bit by bit comparison.
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> .. this is an ssl connection  ..
so the f5 is configured transparently and not the SSL endpoint?

> it fails periododicly
can you please post the corresponding error messages

Author

Commented:
the f5 is not the ssl endpoint. ssl traffic just passes through.
Error message recieved same as tite:
Caught exception: No HTTP response received (possible connection failure)
assuming that this is the message from your web server, the only way to track down that problem would be to sniff n both ends of the F5 and compare the traffic when this error occours.

> .. ran a bit by bit comparison.
then the f5 external interface does net get the response either
you need to find a open tcp connection then, closed by f5 due to timeout, IIRC

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Commented:
We did not find an open tcp connection in our dumps on the f5. We are going to try a sniff of packets on the switch between the server and the f5 to see if anything is droped there. Is there a good way (set of filters) to search for open packets. we're using wireshark.
Thanks

Commented:
If you're using a standard Virtual Server to forward this traffic it could be introducing a delay in the response time your script is expecting.  Since this is a pass thru VS and not doing any upper layer proccessing I would make it a FastL4 VS.
We finaly desided to make the program try again after a failure was caught.

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