Messages in this thread | | | From | David Laight <> | Subject | RE: [-next] Regression: ssh log in slowdown | Date | Fri, 13 Jun 2014 10:05:42 +0000 |
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From: Geert Uytterhoeven > Hi David, > > On Fri, Jun 13, 2014 at 10:49 AM, David Laight <David.Laight@aculab.com> wrote: > > From: Of Geert Uytterhoeven > > ... > >> Note that I'm also using NFS root, which doesn't seem to be affected. > >> I can happily run "ls -R /" on the serial console during the 10 s delay in ssh. > > > > Are you sure that the delay during ssh login isn't just > > a reverse DNS timeout? > > Indeed, the ssh server sends a reverse DNS request twice, with 5s in between: ... > Interestingly, I don't see the forward DNS request after that, which > does happen in the good case.
The forwards request is probably just copying some strange code from 'rshd' that tried to verify the reverse lookup by doing a forwards lookup on the result. That in itself used to cause us grief. The RDNS would (correctly) generate host.bar.baz.co.uk, since the 'domain' in etc/resolv.conf was bar.baz.co.uk the forwards lookup first tried host.bar.baz.co.uk.bar.baz.co.uk then host.bar.baz.co.uk.baz.co.uk one of which always timed out :-( (When the 'search' command was added we could avoid the request that timed out.)
David
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