[avahi] problem with nss_mdns4 doing long timesouts looking up dotted decimals

[Trent Lloyd]

Hi Norman,

On Fri, Mar 23, 2007 at 04:08:49PM -0400, Norman Ramsey wrote:
>  > On Sat, 10.03.07 12:20, Norman Ramsey (nr at eecs.harvard.edu) wrote:
>  > 
>  > > With a recent update, it now takes me 10 or 15 seconds to do any opeation
>  > > involving ssh.  Using strace, I believe I've tracked the problem 
>  > > to avahi's lair.  Here's a fragment of an strace: the NSS opens
>  > > libness_mdns4, which connects to an avahi-daemon socket and asks it to
>  > > resolve a dotted-decimal address.  It takes 5 seconds to time out
>  > > (i.e., it takes 5 seconds for the read() to complete).  For reasons I
>  > > don't understand, ssh does this lookup *twice* to make a connection.
>  > > Result: every little remote cvs operation comes with a 10-second
>  > > delay.  This is driving me crazy; can anyone think of a workaround?
>  > 
>  > If nsswitch.conf is configured correctly (and yours appears to be),
>  > this timeout should only happen if no DNS reverse name is configured
>  > for that IP address, and neither a mDNS reverse name.
> 
> Very odd.  There is a DNS server built into my firewall and this is
> probably causing the problem.
> 
>  > There are several way to work around this:
>  > 
>  > 1) Remove the final "mdns4" from the nsswitch.conf line. This will
>  >    disable reverse mDNS lookups for all IP addresses outside the
>  >    169.254.0.0/16 range. 
> 
> If I remove mdns4, will the earlier mdns4_minimal be sufficient to
> identify hosts in the .local domain on the same LAN segment?

Yes mdns4_minimal only attempts to resolve .local hostnames and reverse
DNS in the 169.254.0.0 range

Cheers,
Trent

> 
>  > The current default behaviour does its best to avoid this timeout, by
>  > putting the DNS lookups first, but you're still bitten because your
>  > DNS doesn't include proper mappings for this IP address.
> 
> Yes.  I blame Bill Gates (the firewall is made by Microsoft).
> 
> 
> Thanks so much for the workarounds!
> 
> 
> Norman
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