Very odd problem - SSL, Virtual Interfaces, and Authorize.net

[Travis Roy]

Okay this is extreamly strange but let me give it a shot to the list..

We have two sites (auth.signull.com and store.signull.com) they both 
have ssl certs for online payment via authorize.net. Now I set up 
auth.signull.com on the primary interface and store.signull.com on a 
virtual interface and set up IP based virtual hosting and all goes 
well, when you go to the IP or the name of either you get to the right 
page be it SSL or non SSL.

Now, since putting them both up we started having problems when I did 
this and the problem is very odd. There's a script that sends 
somebody's credit card information to authorize.net and then that is 
suppose to check it and send the information back to our server via a 
POST so that we can generate a page to show the user what happened (if 
the card was accepted). Now this drove us up a wall because it wasn't 
working and it was timing out. We got error emails from authorize.net 
saying that it was a "time out".

We thought the script might be hanging or something but we didn't see 
anything in the logs about it. After doing a trafshow we started seeing 
the actual connection so we knew they were connecting. Then we started 
doing a tcpdump and had them do the transaction via normal http so we 
could see what was going on. They connected and seem to start some kind 
of handshaking but the apache server never responds.

Now here's where it gets even stranger. Going to the page via IE, 
Mozilla, or even just telnetting to port 80 and issuing the POST that 
way works fine, no issues. Of course authorize.net says that they've 
been doing this for years and it's not their problem. I turn off the 
virtual interface and it works flawlessly, turn it back on, same 
problem.

Anybody have any idea?