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Re: ssh hangs for 5 seconds for a particular machine

On 2015-04-08 13:46:06 -0400, Michael Graham wrote:
> On 8 April 2015 at 13:41, Vincent Lefevre <vincent@vinc17.net> wrote:
> > # /usr/sbin/sshd -D -ddd -p 80 -f /etc/ssh/sshd_config 2>>(ts -s "%.s")
> > [...]
> > 3.315346 debug3: Trying to reverse map address
> So sshd is doing the reverse lookup and fails

Yes, but with nslookup, the failure is *immediate*. So, this doesn't
explain the 5-second delay.

> You probably want to add (or modify) the UseDNS setting to your sshd
> config file.
> UseDNS Specifies whether sshd(8) should look up the remote host name
> and check that the resolved host name for the remote IP address maps
> back to the very same IP address.  The default is “yes”.

Thanks, this solves the problem.

(I've also reported the DNS issue to the sysadmin.)

Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

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