Multiple Domains using one address

[Kevin Darcy]

Yes, it's valid, but there's really no point in having all 3 PTR's since
nothing I'm aware of looks past the first one.

The only pitfall would be if your machines were connecting to a server
which attempted to "authenticate" incoming connections by matching the
results of the reverse lookup with some non-DNS data, e.g. if you had a
protocol something like:

    Client: Hi, I'm www.mydomain2.com. Let's talk!
    Server: According to the reverse lookup, you're actually
www.mydomain1.com. Get lost, imposter!

A more benign form of this same syndrome would be the Received: headers
on SMTP messages, which might show a disparity between the announced
name (in the HELO or EHLO part of the conversation), and the results of
the reverse lookup for the client address.

As a workaround, it might be possible to arrange for all such client
connections to identify themselves as www.mydomain1.com or whatever your
*first* PTR points to.


- Kevin


garabaldi_22 at my-deja.com wrote:

> Newbie:
>
> Is it valid to have multiple domains using the same A records and PTR
> records? That is:
>
> www.mydomain1.com  IN  A 206.110.20.30
> www.mydomain2.com  IN  A 206.110.20.30
> www.mydomain3.com  IN  A 206.110.20.30
>
> 30.20.110.206.IN-ADDR.ARPA.     PTR   www.mydomain1.com
> 30.20.110.206.IN-ADDR.ARPA.     PTR   www.mydomain2.com.
> 30.20.110.206.IN-ADDR.ARPA.     PTR   www.mydomain3.com
>
> If this is valid, are there any pitfalls I should know about? TIA!