If have a draytek 2820 series router that continues to disconnect my ssh sessions after approx. 5 minutes. I suspect it disconnects other stuff as well, because users have been complaining about having to send large emails twice, after receiving errors.
I tried altering the MTU and other stuff to no avail. The router is behind a DOCSYS modem, can this have something to do with it?
Your ssh problem sounds like a problem with an idle connection; I don't think it's the MTU, as that would cause other strange problems.