Reverse lookup mx records and cnames
Mark Andrews
Mark_Andrews at isc.org
Tue May 10 15:12:39 UTC 2005
> Hello.
> I'm not sure what to do.
>
> I have lots of servers which have a record such as
> mail.customerdomain IN A 10.1.1.1
> The MX record for each domain is something like
> customerdomain IN MX mail.customerdomain
Why? "customerdomain IN MX your.server" will work just as
well and be more managable in the long term if you ever
need to change its address.
> This works fine, but you can get a listing of all customers by doing a
> reverse lookup on 10.1.1.1, which is our mail server. This isn't good.
>
> I've thought of two ways to fix this:
> 1. Use a CNAME for the MX record to point to our mail server.
> This isn't allowed or recommended.
> 2. Hack the reverse zone to only return our mail server name.
> This is a hack.
Actually this is quite common. There is no need to have a
PTR record for every A record. In fact it does not scale
as you will find out once you get enough customers to exceed
the DNS/TCP message size of 64k.
Things that care about PTR/A relationships want there to be
a A record to match the PTR record not the other way around.
> Can anyone offer me any advice?
>
--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: Mark_Andrews at isc.org
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