Config check for box swith two nics

[Paul Almquist]

On Friday 18 March 2005 19:55, Rick Stevens wrote:
> Felipe Alfaro Solana wrote:
> > On 18 Mar 2005, at 21:26, GPL wrote:
> >> I am working with a box that has two nics. I want the PUBLIC interface
> >> to use two of my external DNS servers and the INTERNAL interface to
> >> use two of my internal DNS servers. This is not a router as I have not
> >> turned routing on. Not sure my resolv.conf is right. When I try to
> >> ping an internal host by just host name and FQDN it fails. Fine by IP.
> >> Ping by name on Internet side fine.
> >
> > Name resolution is jus that: name resolution... when you try to resolve
> > a name, you don't know beforehand what interface you should use, since
> > you only know the host name. When you want to resolve a name, you ask a
> > name server, but you can't distinguish between internal or external
> > queries.
> >
> > AFAIK, what you want to do is impossible.
>
> You can't direct a DNS query to a specific DNS server, that's true.
> You can, however, put multiple DNS servers in your /etc/resolv.conf
> file.  I'd suggest you put the external DNS servers in first, and your
> internal server in last.  If the name resolution doesn't happen on one
> of the external servers, it'll revert to the internal server.

"The servers in nameserver lines are contacted in order; as long as the first 
one continues to answer queries, the others will be ignored.  If a problem 
occurs, the query times out and the next name server is tried.  Each server 
is tried in turn, up to four times.  The time out interval increases with 
every failure."  Unix System Admin Handbook  3rd ed., p412
So if the first one responds with a not found the others will not be 
consulted.  The assumption is the they all have access to the same data, the 
public DNS servers.

>
> BTW, only the first three DNS servers in /etc/resolv.conf are used.


-- 
Paul Almquist
paul at almquist.name
Eau Claire, WI  USA