FWIW, since you now have one, the one thing I remember in specific being a problem was long-term TCP sessions. There's a setting that's a timeout for how long such sessions can last. I don't know that I understand the concept of this setting in general (I suppose to clear out queues from TCP sessions that got dropped on the floor instead of exiting normally or being abnormally terminated), but it's there, and the default is like 15 minutes or something. This will, apparently, kill any TCP session that's been open for 15 minutes, no matter if it's being used. Or maybe there's an idle thing. I don't quite remember, but I do remember it turning off legitimate TCP traffic. Anyway, the setting is there as a global setting, but the global setting doesn't actually affect anything. You have to set it in the connection-specific area.

This took a supposed expert I was dealing with over a week to figure out.