Yes, DEBUG3.

The trace from a working client and a non-working client are identical, except
that the non-working one stops when it gets to the point of waiting to receive
the key from the client.

ssh -vvvv on the client sides hangs at "key sent"...

On 2014-10-06 11:36, Derek Murawsky wrote:
> Have you run the server(s) with debugging turned up? If you're seeing this
> regularly, it might make sense to run with debug logging for a week and see
> what your server is seeing. Have all your clients retry with debugging up as
> well, and then compare notes next time this happens. 
> At a guess, it sounds almost like sshd is hanging. Otherwise it should close
> out on its own after about 30-90 seconds from a TCP timeout. 
> -D
> 
> On Mon, Oct 6, 2014 at 12:41 PM, Yves Dorfsman <[email protected]
> <mailto:[email protected]>> wrote:
> 
> 
>     We've run into this weird AWS issue 3 times now in a week, never seen it
>     before:
> 
>     A Linux instance becomes unreachable via ssh from some ip addresses. If 
> you
>     try to ssh from those addresses, it just hangs, for ever, until to ctrl-c 
> out
>     of it. Yet you can ssh from other ip addresses without any problem.
> 
>     The ip addresses that work and that don't seem random, some are outside 
> AWS,
>     some inside, even on the same subnet. When we run in DEBUG3 mode, we see 
> that
>     the client sent it's key, while the server waits for the said key, and 
> sits
>     there waiting. The few similar issues (ssh hanging at key exchange) we 
> found
>     when googling were solved by changing MTU!
> 
>     The only resolution we have found so far is to stop/start the instance 
> and get
>     a new ip (tbh, we haven't tried to just reboot).
> 
>     Has anybody run into this? Any idea what's going on?
> 
>     --
>     Yves.
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> 
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-- 
Yves.
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