Is my DNS set up properly for reverse lookups?

[Steven M. Schultz]

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Hi -

> From: Barry Margolin <barmar at bbnplanet.com>
> >444 PTR www.forstdomain.com.
> >444 PTR www.seconddomain.com.
> 
> Yes.  However, I don't recommend having multiple PTR records for the same
> address.  It's legal, just potentially confusing.

	It also "breaks" the TCP wrapper ("tcpd") because the POSIX
	interface 'getnameinfo()' can't deal with multiple names being
	returned by a reverse lookup.  The older 'gethostbyaddr()'
	routine can deal with the situation but if you're on a system
	for which 'tcpd' has been IPv6'ified and/or POSIX'fied then
	'tcpd' will declare a "mismatch".

	The reason this happens is that 'tcpd' first does a reverse lookup:

	if (getnameinfo(sa, sa->sa_len, host->name, sizeof(host->name),
			    NULL, 0, NI_NAMEREQD))

	Note:  there is no provision for returning multiple names.

	During the triple crosscheck (addr->name, name->addr, addr->name)
	it is possible to have a mismatch occur	depending on which name gets
	returned by 'getnameinfo'.  I've seen it happen a couple times.

	So while multiple in-addr.arpa entries are legal there is code (fairly
	new/recent code at that) which doesn't/can't deal with it.

	Steven Schultz
	sms at wlv.iipo.gtegsc.com