curious behavior with ssh OpenSSH_3.9p1

Iain Morgan imorgan at
Tue Sep 11 02:22:09 EST 2007

On Fri, Sep 07, 2007 at 23:31:44 -0700, leel wrote:
> Sirs,
>   I'm trying to figure out why ssh (red hatOpenSSH_3.9p1, OpenSSL 0.9.7a 
> Feb 19 2003)
>  hangs  to a solaris  (Sun_SSH_1.1, SSH protocols 1.5/2.0, OpenSSL 
> 0x0090704f) after some time. the times seem
> variable. the process is still alive on the remote site.
> I can connect to another red hat machine on the same site with longer 
> sessions.  This computer has an older
> version of openssh (red hat OpenSSH_3.4p1, SSH protocols 1.5/2.0, 
> OpenSSL 0x0090602f)
> This did not happen until I've changed
> my modem/router to a linksys wcg200. when the red-hat machine connects 
> to a solaris machine at work
> there are no hang ups.  I fear that the combination of the modem, 
> solaris and ssh is causing the problem
> and I have tried every angle I could think of the fix this.  Also with 
> the same pc under windows xp
> ( this is a dual boot system) it does not hang since I am using ssh to 
> execute a command to create a xterminal
> from the remote computer but using putty or ssh on my pc eventually hangs..
> I've updated the sshd_config file to keep the session alive but to no 
> avail. other programs such as downloading
> and internet radio don't seem to be affected. The download lasted for an 
> hour.
> If you have time, do you have any suggestions or websites on why this is 
> causing the problem?
> do you have any documentation on how ssh works and whether there are 
> problems with cable modems
> and how do check if the cable modem is blocking the keepalive signals?
>  I would like to make sure that it's the particular modem/router I am 
> using  thats causing the problem so that
> I can determine that I just need a different modem/router.
> Thank you for reading this
> Louise Lee

I've occasionally seen situations where certain Linksys (and NetGear) routers
appear to break idle ssh sessions. This seems to happen even with TCP keepalive
enabled. The solution has usually been to enable the ServerAliveInterval
mechanism in the client ssh_config (or ~/.ssh/config). 

I don't recall if the Sun SSH 1.1 implementation supports the ServerAliveInterval
or ClientAliveInterval mechanisms. I suspect it does not, in which case this
solution won't work for you.

Iain Morgan

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