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TCP timeout of 1 hour before can be reconnected (using same ip/port pairs)

The TCP server and client is separated by a PIX firewall. When TCP client is physically disconnected and then reconnected after 30 minutes (TCP client software will re-try every 20secs if reconnection failed again, using same IP/port), it will be connected sucessfully only about an hour later.

Checked on the server and client systems that the TCP state transition is functioning correctly (i.e. no CLOSE_WAIT or FIN_WAIT on the server and client system). The SYN request from the client did reach the firewall LAN.

Check on the PIX firewall using "show conn" and the flag always shows "U" i.e UP irregardless whether there's TCP connection or not. Is this the correct command to use to check active connection?

Will appreciate if anyone has any idea what could be the possible cause for above problem in relation to PIX firewall.

Thanks in advance.

2 REPLIES
Cisco Employee

Re: TCP timeout of 1 hour before can be reconnected (using same

Are you saying that after you disconnect the client, then reconnect it a while later, it takes about an hour for the connection to be successful?

If the client sends out a new SYN packet with the same port numbers (and the same sequence numbers?), but the PIX already has an UP conection for this, I would imagine the PIX probably drops the packet. It will continue to do this until the TCP connection in the PIX times out, then a new one will be built when it sees the SYN packet again. You could verify this by looking at the syslog, you'll see messages that describe exactly what's going on.

New Member

Re: TCP timeout of 1 hour before can be reconnected (using same

>>Are you saying that after you disconnect the client, then reconnect it a while >>later, it takes about an hour for the connection to be successful?

Yes.

>>If the client sends out a new SYN packet with the same port numbers (and >>the same sequence numbers?), but the PIX already has an UP conection

Yes. Same port number and seq number. And the PIX still hv the UP connection.

>>for this, I would imagine the PIX probably drops the packet. It will continue >>to do this until the TCP connection in the PIX times out, then a new one will >>be built when it sees the SYN packet again. You could verify this by looking >>at the syslog, you'll see messages that describe exactly what's going on.

The PIX is not under my control ....so can't easily check the syslog. But I agree with what you suspect. Believe "timeout conn" shall solve my problem then (found that the default connection timeout is 1 hour).

Thanks a lot for your help!.

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