closing all inactive server connections

[Ted Zlatanov <tzz@lifelogs.com>]

Very often, my company's VPN will disconnect and my server connections
will hang.  I have to manually go into the server buffer and hit `C' on
each server to close the connection, then C-g to cancel the ensuing
timeout.  I have 8 servers (NNTP and IMAP) so this is slow and annoying.
My questions are:

1) is there a way to close all the server connections without the
connection timeout?

2) can I set the time a connection becomes inactive (so it needs to be
reopened) to a few seconds?  It seems to be several minutes right now.
Perhaps this is not a Gnus attribute but a system-level TCP setting, I
don't know how Gnus and Emacs manage TCP connections.

Thanks
Ted