Question of forwarders vs. caching-only

[Barry Margolin]

In article <p81I3.6$jU2.310 at news.rdc1.md.home.com>,
Don Awalt <awalt at rdaconsultants.com> wrote:
>I have a question, I can set up a DNS for my own (non-authoritative) subnet
>via a caching-only server. This appears to go to root DNS servers to resolve
>names not in its own cache.  Or, I can additionally add the names of
>"forwarder" DNS servers to forward the queries that cannot be resolved
>locally.
>
>When would I just let the DNS server cache via the DNS root servers, vs.
>specifically forwarding? I am thinking forwarding makes sense when you can
>point to another DNS on your own subnet vs. going to a root server
>somewhere, but does it always make sense to forward to an authoritative DNS
>server for your subnet (even if it's across a WAN, as are the root servers)?
>When not to forward?

Forwarding is mainly useful in two cases:

1) You're using split DNS, i.e. you have an internal server that isn't the
one that your domain is delegated to from the root servers.  The server on
your subnet needs to forward to this internal server to see the internal
version of your domain.

2) To share the cache of another internal server, which can reduce the load
on your Internet link.

Also, if you forward to a server that's authoritative for your domain, you
don't lose the ability to look up things in your local domain if the
Internet connection goes down.

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