What's Wrong with CNAMEs? (was Re: Prefixless domains)

Kevin Darcy kcd at daimlerchrysler.com
Tue Mar 26 23:22:12 UTC 2002


Simon Waters wrote:

> Kevin Darcy wrote:
> >
> > I have a question for all of you snobs who avoid CNAMEs like the plague:
> > how do you deal with reverse records when multiple names must resolve to
> > the same IP address? Multiple PTR records don't work, of course. What
> > reasonable alternative is there, besides making one of the names be an
> > A record, with the other (n-1) names being aliases to that name? Can't do
> > that with zone-apex names, of course...
>
> canonical IN A 127.0.0.1
> fred IN A 127.0.0.1
>
> 1.0.0.172.in-addr.arpa. PTR canonical
>
> Why do multiple PTR records not work, you mean the application
> you are thinking of can not handle them correctly? I think the
> standards say they should work, but the standard doesn't say
> what you do with them.

Well, the "application" I'm thinking of is the gethostbyaddr() interface, and
thus by extension everything that uses it. This phenomenon is so widespread,
I think it is fair to say that multiple PTRs "don't work" in any practical
sense.


- Kevin





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