From: Wietse Venema (no email)
Date: Fri Nov 27 2009 - 13:18:15 EST
> Greg A. Woods:
> > There _should_ be one PTR for every _valid_ hostname using a given IP
> > address.
> Statements such as above remind me of silly knights fighting windmills.
> There is a difference between "right" and "useful", and it even
> depends on where they are used - server or client side.
> Multiple server A records are useful. More in the case of HTTP,
> less in the case of SMTP which uses indirection via MX records.
> (For a discussion about domain-in-a-box applications, see some
> actual measurements that I did earlier this year).
> One PTR per A record is not useful. The server end will not know
> what client name to use.
That is, one PTR per A record, in the case of multiple A records
for the same IP address.
> On the other hand, it is right when every PTR record has a matching
> A record that resolves to (among others) the PTR record's address.