On 10 December 2011 19:06, Rob Malpass <linux@???> wrote:
> Hi all
>
>
>
> My 64-bit lucid box has developed a rather irritating fault which my lack of
> knowledge can't fix. While the ethernet side of things looks solid - I'm
> getting random disconnections when I'm vnc'd or ssh'd into it. Also (again
> periodically and without apparent reason) it refuses to let me in either
> through vnc or ssh.
>
>
>
> I've installed wireshark and looked in /var/log but such information as is
> in either of these is all Greek to me! FWIW the client is always a Windows
> 7 machine. Here's what I've checked:
>
> * Firestarter - nothing obvious and besides which - with no change to the
> settings sometimes it lets me in, sometimes not - ditto establishing a new
> connection.
>
> * hosts.equiv, hosts.allow
>
>
>
> What I've not checked:
>
> * network cable - but there are no obvious dropouts in a terminal pinging
> the router with the -t option
>
> * using a different client which may be Windows or something else.
>
>
>
> Anybody know is this is a known issue?
>
This could be any number of things.
Some places to start
1) It the problem the sshd?
You can ssh from the server back to itself, and at the same time
connect from the windows 7 client.
When the Windows 7 client disconnects, does the server back to itself
also disconnect.
If only the Windows 7 client disconnects, you know that the problem
lies outside of the ssh server.
So, problem is then down to one of two things:
a) Network fault
b) Windows 7 configuration.
Looking a (b)
Things to look for are:
1) Network bouncing. Look in the windows event log for any issues. It
can take a long time scanning the windows event log before you find
anything useful.
When the network interface goes down in Windows, all TCP connections
using it are also disconnected immediately.
In Linux, when the network interface goes down, TCP connections remain
until standard TCP keepalive timeouts or other timeouts occur.
So, a bouncing network connection will not kill Linux TCP connections.
2) Windows Group policy
Windows can periodically scan all network connections and kill any it
thinks are not permitted.
For example, you could manually set up a firewall permit rule on the
Windows 7 machine. It will work for a bit, and then the scan will undo
the manual permit setting, and also disconnect the TCP sessions.
A good test could be booting a Linux Live CD on the Windows 7 machine,
and see if it has problems with ssh sessions or not.
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