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Steve_A_130918's avatar
Steve_A_130918
Icon for Nimbostratus rankNimbostratus
Dec 19, 2013

SMTP Intermittent Connection Failure

Hi   I have a VIP fronting 3 Exchange 2007 transport hubs on smtp port 25. It appears to work correctly for 99% of the accessing servers, but for a couple it times out intermittently. You can tes...
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Steve_A_130918's avatar
Steve_A_130918
Icon for Nimbostratus rankNimbostratus
Dec 30, 2013

Managed to get a tcpdump against the source server at the F5.

 

First (successful) connection show the usual syn / syn,ack / ack sequence, ending with a fin,ack / ack / fin,ack / ack sequence.

 

Second (unsuccessful) connection shows syn / syn,ack / syn / syn,ack / syn / syn,ack / syn,ack then nothing and the connection drops.

 

So it looks like the remote server is responding but the source server isn't accepting the response as valid and keeps retrying until it times out.

 

I can email the dump file if anyone is willing to run it through wireshark and give me an opinion.

 

Thanks

 

Steve