Debian server NOT responding to SYN packets (randomly)

Hi Folks,

I am seeing some extremely strange behavior between my front end webserver (Sun Java Web Server V7.0U1) on Solaris 10 and a JBoss Server (JBoss 4.2.2) on a Debian box). Every once in a while, the web server will have a connection time out with the jboss server (which is part of a 3 machine pool) and the webserver will rightfully shunt that server's load over to one of the other jboss servers, however...this session switching forces our users to have to reauthenticate, as the session data is not shared between jboss machines. The web server will then continue to redirect all traffic for the "down" web server until the health check thread runs again on the web server and it sees that the jboss server is not really down.

Well, after much searching, we have discovered that on those connections that time out, there is no response from the jboss server to the SYN packet sent from the web server!!! We see it leave the webserver (via snoop) and see it arrive on the jboss server (via tcpdump), but no SYNC/ACK is ever returned! During a "good" conversation we see all the appropriate handshaking and data transfer just as we'd suspect.

Has anyone else here ever run into this situation? I did look at the individual SYN packets, and there is no difference between a "good" SYN and a "bad" SYN...they look the same.

In a word....I need "HELP"!

Thanks in advance!

-Emmett