Dear all, I have encountered a problem with our Squid server, where it does not seem to proxy a certain connection. The problem appeared on the 19th August. The last configuration change on the squid server was on the 16th. I rolled back the change, but it did not solve the problem, although, the change was unrelated. A diff between the current and previous squid.conf files did not show anything relevant. The server named t2nl-app301 has this entry in the squid.conf acl t2nl-app301 src 10.205.8.193/255.255.255.255 http_access allow t2nl-app301 All HTTP requests sent via the squid service successfully proxied except one. t2nl-app301 -> Squid service -> Chaos : squid always passes back a 503 Service unavailable. Summary of tests: A direct connection (no proxy used) from t2nl-app301 -> Chaos : result 401. A direct connection (no proxy used) from Squid server -> Chaos : result 401. A connection using the proxy, from Squid server -> Chaos: result 503. A connection using the proxy, from t2nl-app301 -> Chaos : result 503. A tcpdump of the proxied connection between: t2nl-app301 -> Squid service -> Chaos connection shows the conection from t2nl-ap301 to Squid server, but no packets are sent from Squid server to Chaos. There is an entry in the access.log that reads: 10.205.8.193 - - [24/Aug/2010:14:38:03 +0200] "GET http://chaos:5780/invoke/VTEMS.Flows/receive HTTP/1.0" 503 1596 TCP_MISS:NONE I am at a loss of how to diagnose this problem. Has anyone got any ideas of where I should look? I do not see how this could be a firewall problem because one can telnet onto the port from the Squid server and get a responce. Regards, JK.