This is a question I posted to the RHEL3 mailing list but didn't get a response:

"We are currently running squid-2.5.STABLE3-6.3E.9 on one of our RHEL3 proxy servers because updating to the latest (squid-2.5.STABLE3-6.3E.14) seems to break any kind of tunelling, ie. things like instant messaging ports and ssh using proxytunnel (http://proxytunnel.sourceforge.net/). Has anyone else experienced this problem with the Squid updates from RHN?"

I was wondering if anyone running Centos has any advice/info on this?