caching-only DNS and forwarders

[Barry Margolin]

In article <m3hfe5qh0d.fsf at localhost.localdomain>,
Pat Railswak  <nobody at example.org> wrote:
>I've set up my caching-only DNS and was left with a question.
>
>With normal home use of caching-only DNS why should I use the
>"forwarders" option in /etc/named.conf when one just gives it the 
>same DNS listed in /etc/resolv.conf?  The DNS HOWTO (and others)
>have said this is good, but I don't see why. The same external DNS are 
>queried as soon as the local DNS doesn't find the name in its cache
>with or without using forwarding it seems to me.  Is there any test 
>I can do to show what's happening?  I don't like duplicating the IPs 
>in two files if not helpful. Can someone explain better than the HOWTO
>or my "DNS & BIND" book?

If you don't have "forwarders", it will work its way down the DNS hierarchy
from the root servers, not go to the servers in /etc/resolv.conf.  named
doesn't consult resolv.conf at all, only client applications do.

If you point to your ISP's servers, they're probably closer to you than the
root servers and the remote sites' servers.  They may also have the answer
to your query cached because another customer already looked it up
recently.  So instead of having to make several queries to distant servers,
you may get an answer with one query to a nearby server.

On the other hand, this makes you dependent on your ISP's servers.  If
they're not reliable, you would probably be better off letting your server
do its own lookups.

-- 
Barry Margolin, barmar at bbnplanet.com
GTE Internetworking, Powered by BBN, Burlington, MA
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