[Bug 1667] sshd slow connect with 'UseDNS yes'

bugzilla-daemon at bugzilla.mindrot.org bugzilla-daemon at bugzilla.mindrot.org
Wed Nov 4 09:04:33 EST 2009


--- Comment #10 from Darren Tucker <dtucker at zip.com.au> 2009-11-04 09:04:32 EST ---
(In reply to comment #9)
> [root at corvus ~]# time host -t A flux.arc.nasa.gov. ns1.arc.nasa.gov.
> flux.arc.nasa.gov has address
> real    0m5.026s

There's your problem: your DNS is taking 5s to respond.  I'm surprised
that it's happening for A records too given what I saw in the packet
trace, but I expected to see this for AAAA.

So your DNS (or resolver) is slow, and that's compounded by something
in PAM making multiple trips to the well.

The options I can think of are:
 * fix your DNS or resolver
 * make your resolver send only IPv4 requests
 * live with UseDNS=no
 * disable PAM.

You also could try building OpenSSH with "configure
--with-cflags=-DBROKEN_GETADDRINFO".  This will force the use of the
built-in getaddrinfo replacement that happens to speak only IPv4, but
it probably won't help the PAM bits.  I suspect this will make minimal
difference though.

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