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Re: Pick a name, any name...



On Fri, Nov 29, 2002 at 01:11:34PM -0800, John H. Robinson, IV wrote:
> because with a A record one lookup -> IP address(es)
> with a CNAME one lookup -> another lookup -> IP address(es)
> 
> CNAME cause you to at least DOUBLE the DNS lookups, DOUBLING the
> potential timeouts, DOUBLING dns load

Not necessarily. It depends a bit on the intelligence of the DNS server and
the client. A DNS response has an "additional section" for stuff like this.
If you so a "dig net. ns" you will see that not only are you provided with a
list of nameservers in the answer section, but also all their IP addresses
in the additional section. Thus avoiding the second lookup.

The same trick can be applied to CNAMEs. It also applies to MX records
(which may only specify the name of a server, not IP address).

Try:

dig freshmeat.net. mx
dig www.freshmeat.net

for more examples.

> can you do it? certainly. should you be aware of the effects WHEN you do
> it? yes. you may break the rules only after you understand the rules.

There is no rule. The designers of DNS thought of this and solved it.

-- 
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Support bacteria! They're the only culture some people have.

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