Thanks for the pointers. Tracking connections is a little tough, since there are thousands of connections to the front end, and the pool/node is a load balancer. finding the one SYN that isn't ACKd is like finding a needle in a needle stack :-)
One thing to note is that I replaced some old Linux servers running Apache using mod_proxy with the LTM. We never had this issue until we went to the LTM. I am trying to figure out which of the hundreds of differences is causing the problem, and if there is a way to adjust the LTM so that it doesn't behave this way. I suppose increasing the SYN retry is an option. Would using an LB::reselect work if there is only one node in a pool?
Thanks,
Kenny
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