[Dovecot] Hostname passed to PAM as rhost

[Jethro R Binks]

On Mon, 26 Sep 2005, John Peacock wrote:

> Actually, this level of paranoia is not useful, since it will fail to 
> correctly operate in the very real case of co-hosted boxes.  There can 
> only be (in practice) a single mapping from IP => hostname (via 
> in-addr.arpa), but there can be virtually limitless hostname => IP maps.

Technically that is incorrect.  See RFC 2181 10.2, which explicitly 
states:

  "Confusion about canonical names has lead to a belief that a PTR
   record should have exactly one RR in its RRSet.  This is incorrect,
   the relevant section of RFC1034 (section 3.6.2) indicates that the
   value of a PTR record should be a canonical name.  That is, it should
   not be an alias.  There is no implication in that section that only
   one PTR record is permitted for a name.  No such restriction should
   be inferred."

Apparently older implementations of gethostbyaddr() didn't like this, but 
that isn't the case in modern implementations.

However, your comments are probably correct in practice because those 
implementing multiple hostnames -> single IP rarely put in the 
corresponding multiple PTR records from the in-addr.arpa entry back to 
each of the hostnames.

Jethro.

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Jethro R Binks
Computing Officer, IT Services
University Of Strathclyde, Glasgow, UK