[AusNOG] PTR Records

[Mark Andrews]

In message <1317382514.1778278.1416276314750.JavaMail.yahoo at jws10688.mail.bf1.y
ahoo.com>, Mark ZZZ Smith writes:
> 
> 
> 
> 
> >________________________________
> > From: Colin Stubbs <colin.stubbs at equatetechnologies.com.au>
> >To: Mark Andrews <marka at isc.org> 
> >Cc: "ausnog at lists.ausnog.net" <ausnog at lists.ausnog.net> 
> >Sent: Tuesday, 18 November 2014, 12:46
> >Subject: Re: [AusNOG] PTR Records
> > 
> >
> >
> >What Mark said.
> >
> >I'd also note, that while the value returned by the PTR request is
> > *intended* to be another valid RR (A, AAAA etc)... it can actually
> > be any ASCII string.

More correctly it can be any domain name.  That said within
in-addr.arpa and ip6.arpa the PTR records which correspond to the
reverse mappings of IP addresses are expected to be hostnames (LDH).

> If you want to have a bit of fun, change PTRs for router interfaces to
> "censored" or similar. When I did something similar (I wanted to obscure
> something just to that it wouldn't be used temporarily), traceroute just
> displayed it.  IOW, traceroute wasn't validating in any way the PTR
> string returned, it was purely displaying it.

"censored" is LDH so you have no way of knowing if it or the library
routine checked.  Note also some routines within a library may care
while others may not.  getnameinfo / gethostbyaddr usually care,
but not always, whereas res_query / res_search won't care despite
both being in the same library.

Mark
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org