[CentOS] /etc/resolv.conf - Number of Nameservers

Mon Mar 10 06:32:07 UTC 2008
Manish Kathuria <mkathuria at tuxtechnologies.co.in>


On Sun, 2008-03-09 at 22:02 -0700, John R Pierce wrote:
> Manish Kathuria wrote:
> > What is the maximum number of nameservers mentioned in /etc/resolv.conf
> > which will be queried while looking up a hostname or IP address in the
> > present version ? Earlier implementations had a ceiling of 3 name
> > servers which could be queried. Has there been any increase ?
> >   
> 
> only one server is ever queried.  only if it if it can't be reached at 
> all will it fall back on the 2nd one (and if that can't be reached, the 
> 3rd)   a answer of 'host not found' from the primary server does /not/ 
> trigger any fallback, instead it returns "not found".
> 
> so, why would you need more than 3 ?   DNS servers should have a .9999 
> uptime.


The idea is to switch between multiple internet links for the same
internal network, without making frequent changes to /etc/resolv.conf.
The ISPs here don't allow DNS look ups from an IP not belong to their
address, so a number of look up requests get denied when the outgoing
connection is through another ISP. Of course, I can run a caching
nameserver on the small network or use Open DNS servers but that adds to
the delay.

Thank you,

Manish