From: Wietse Venema (no email)
Date: Fri Nov 27 2009 - 13:09:34 EST
Greg A. Woods:
> There _should_ be one PTR for every _valid_ hostname using a given IP
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.
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.