Caching nameserver for mail servers

[Barry Margolin]

In article <20000427155056.A394 at lucifer.bart.nl>,
Jeroen Ruigrok van der Werven  <jruigrok at via-net-works.nl> wrote:
>Hi,
>
>I am thinking about the pros and cons of setting up a caching nameserver
>on a mailserver, as to eleviate some of the lookup stress for the
>mailserver.
>
>Does anyone have some pointers for me about this setup?
>
>The nameserver will be a 8.2.2-p5 based BIND.

If you have multiple mailservers, it would probably be better to have them
all use a common nameserver, so that they can take advantage of the
combined cache.

One pro of using a separate caching server for mail from your other uses is
that its cache won't be full of lots of unneeded www.<domain> entries.  But
the con is that it won't be able to take advantage of NS records that might
have been cached when looking up those entries for other clients, so it
will have to make redundant queries to root and TLD servers.

If some of the clients of your regular caching server are customers who run
their own mailservers, then its cache will probably have many entries that
your mailserver could use, so it might be better to use the same server.

As you can see, there are benefits to each approach, and I don't think
there's any easy way to quantify which is better.  I suggest you just try
it and see how it goes.  I'm not sure what you need to know about the
setup, since there's nothing special about it.  Just run named on the
mailserver and configure its /etc/resolv.conf to point to 127.0.0.1.  You
might want to use the "allow-query { localhost; }" option in named.conf to
prevent anyone else from using it as their server.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Burlington, MA
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