[asterisk-users] asterisk and DNS

[Tzafrir Cohen]

On Fri, Feb 06, 2009 at 12:10:52PM +0000, Jan-Aage Frydenbø-Bruvoll wrote:
> 
> Hi,
> 
> nscd (name server caching daemon) is a part of most Linux 
> distributions as well - maybe that'd help you if your DNS server is 
> unstable.

The NSCD caches names from the name switch. Those names are not only
'hosts'. They can also be user names ('passwd') or just about anything
from /etc/nsswitch.conf .

However using it to cache hosts is considered a bad idea normally. IIRC
it is due to incorrect caching of bad replies.

ncsd.conf has the following:

# hosts caching is broken with gethostby* calls, hence is now disabled
# per default.  See /usr/share/doc/nscd/NEWS.Debian.
        enable-cache            hosts           no

And the NEWS file reads:

glibc (2.5-5) unstable; urgency=low

  Since this release, hosts caching in nscd is off by default: for some of the
  libc calls (gethostby* calls) nscd does not respect the DNS TTLs.  It can
  lead to system lockups (e.g. if you are using pam-ldap and change the IP of
  your authentication server) hence is not considered safe.

  See debian bug #335476 and how upstream answered to that in
  http://sourceware.org/bugzilla/show_bug.cgi?id=4428.

 -- Pierre Habouzit <madcoder at debian.org>  Sat, 28 Apr 2007 11:10:56 +020

> 
> Best regards
> Jan
> 
> > Julian Lyndon-Smith wrote:
> > > We've just had the problem where our DNS server went down, and * started 
> > > to act "funny".
> > >
> > > Is the best solution to install a local DNS server on the * box, and 
> > > have no other DNS servers ? - this is an internal app, no need for any 
> > > external DNS resolution at all.
> > >
> > > Julian.
> 
> 
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-- 
               Tzafrir Cohen
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