S-Nat and XML transactions
The load balancers we're using work as NAT devices (Network Address Translation), so we have a private network behind them with all of our servers attached and the public network on the other side of them. All traffic to/from our servers goes through the load balancers, making for a firewall. To allow the web servers to talk to sites they want to visit (or request services and information from), NAT is used to allow for the public address of the load balancers to be used in the request to the servers on the other end.
This works well for most things I've tried. OS updates install just fine (rather quickly over the large pipes our data center has, I might add). Payment related data works just fine (or at least it does now that I have it fixed). I can open an X-Windows session and browse websites just fine. But the problems start to come in when we try to pass XML from our new servers to our office location. I get a 500 read timeout almost instantly. I haven't spent a whole lot of time on this, but it's sure puzzling how most services can work and one (which we use heavily on the site I haven't moved yet) refuses to work.
I'm sure I'll come across the answer soon enough, but until then I'll scratch my head a while.