[dns-operations] how common is a 66-record answer section, i wonder?

Paul Vixie paul at vix.com
Mon Aug 14 05:40:01 UTC 2006

> 	I've never seen the benefit of multiple pointers in the
> 	reverse tree.  People just keep adding them until they
> 	exceed the ability of the protocol to return.  In reality
> 	nothing depends on there being a matching ptr for a address.
> 	The reverse however is not true.

i realize that .rhosts is dead, but there was a time when being able
to check gethostbyname(gethostbyaddr(getpeername(s))) == getpeername(s)
was valuable, and being able to enumerate all of the owners of A RRs
that had the same rdata was therefore valuable.

it's still in common use for anti-spam MTA's.  postfix has an option
for "don't allow e-mail from hosts who don't have PTRs" as well as
"don't allow e-mail from hosts whose PTR isn't the same as their HELO"
as well as "don't allow e-mail from hosts who aren't in the A RRset
for the HELO name".  i use all three, and i depend on them, and i like
them, and so i find A-vs-PTR symmetry to be valuable, even w/o .rhosts.

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