[ALUG] Mostly-OT: Strange ADSL issues

[Wayne Stallwood]

On Sat, 2006-10-07 at 10:52 +0100, Mark Rogers wrote:
> I have two ADSL lines from completely different providers (Demon and The
> Phone Coop (www.thephone.coop), both behaving the same. The lines are
> both in the Peterborough area but on different exchanges. Although this
> isn't a Linux problem I think Linux is most likely to give me the tools
> to resolve it.
> 
> Basically, some of the time the ADSL lines just work: I can browse the
> web, collect email, download ISOs, etc.
> 
> However the rest of the time (and its becoming increasingly "most of the
> time") I can't. To all intents and purposes the connection has gone.

Very strange.

Some of the things you mention below almost sound like a MTU miss-match
problem, but why this would be intermittent I am not sure. MTU problems
could explain why a ping works until the packet size is increased and
could also explain why traffic encapsulated by your VPN may work while
other connections fail.

What are the line stats on your routers showing ? It doesn't sound
completely like an ADSL/Line problem but the intermittent nature sort of
points in that direction. 

When you are in a state of not being able to start a new ssh connection
can you still telnet to port 22 of an external ssh server and see the
server banner (or do you get connection timed out even doing that)