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Re: remote port forwarding unstable

On Mon, 19 Oct 2009, Adriana Rodean wrote:
> I always do a remote port forwarding with openssh on 1026 port let's
> say ( ssh -R 1026:localhost:55555 ). Most times the port is opened on
> remote machine. But sometimes i notice that ssh can't do remote port
> forwarding to that port 1026. I looked on the remote machine (netstat
> -an) and no one is using that port, so the port is free.
> Only way to fix this is do a remote port forwarding to another port
> lets say 1056, successfully done, then try again and do it for 1026,
> this time remote port forwarding successfully works... Sometimes it
> works if i try again with 1026, but other times i need to open another
> port then try again with 1026 port...
> [..]
> I use version of OpenSSH 5.1p1 on remote machine and the client is
> OpenSSH for Windows 3.8.1p1

Nobody uses the port, but it is still in TIME_WAIT state.
Usually openssh uses SO_REUSEADDR to say the kernel that the
port can be reused while in TIME_WAIT state, but to avoid X11
man-in-the-middle attack the portable version of OpenSSH
5.1 does not set it if you have X11UseLocalhost=no.

So, you should either wait a little after each closing of the
port before trying to use it again, or set X11UseLocalhost=yes.


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