[Dnsmasq-discuss] Feature Request(s)

/dev/rob0 rob0 at gmx.co.uk
Fri Mar 16 00:37:45 GMT 2012


On Thu, Mar 15, 2012 at 03:14:08PM -0500,
   richardvoigt at gmail.com wrote:
> On Thu, Mar 15, 2012 at 2:34 PM, /dev/rob0 <rob0 at gmx.co.uk> wrote:
> 
> > On Thu, Mar 15, 2012 at 10:24:44AM -0700, Rob Zwissler wrote:
> > > Yah, seems to me it would make more sense to key off the IP 
> > > address (or have that come first in the config) as it seems to 
> > > make more sense to organize zone files by IP, and since you can 
> > > have multiple A's per IP but not multiple IPs per PTR.
> >
> > You CAN have as many PTR records as you want on any name. 
> > However, it's unlikely to do anything useful.
> >
> Since the PTR name contains the IP, by definition different IPs
> means different PTR records.

There is nothing preventing you from having as many PTRs on a single 
in-addr.arpa name as you might wish. Here's a silly example:

$ dig 78.247.23.216.in-addr.arpa. any @216.23.247.74

;; QUESTION SECTION:
;78.247.23.216.in-addr.arpa.    IN      ANY

;; ANSWER SECTION:
78.247.23.216.in-addr.arpa. 7200 IN     SOA     ns.slackbuilds.org. hostmaster.ns.slackbuilds.org. 2012031502 28800 7200 864000 7200
78.247.23.216.in-addr.arpa. 7200 IN     NS      ns2.slackbuilds.org.
78.247.23.216.in-addr.arpa. 7200 IN     PTR     c78.nodns4.us.
78.247.23.216.in-addr.arpa. 7200 IN     PTR     look.here.another.ptr.78.247.23.216.in-addr.arpa.
78.247.23.216.in-addr.arpa. 7200 IN     PTR     third.ptr.wow.
78.247.23.216.in-addr.arpa. 7200 IN     A       216.23.247.79
78.247.23.216.in-addr.arpa. 7200 IN     TXT     "A TXT record also."
78.247.23.216.in-addr.arpa. 7200 IN     TXT     "CNAME record is the one thing we cannot do."

SOA, NS, three PTRs, A, and two TXTs on that name. Silly stuff, yet 
quite within the range of DNS legitimacy. My point is, however, that 
resolvers won't know what to do with multiple PTRs on the same name.

Similarly, you can add PTR records in "forward" zones. There's no 
limit to the fun, fine in DNS. But no resolver would ask for these 
PTRs (unless in an RFC 2317 CNAME reference.)

See, I even missed the trailing dot on the middle PTR for fun. Or 
pure sloppiness. :)

In <877gylpki8.fsf at benfinney.id.au>
On Fri, Mar 16, 2012 at 09:27:59AM +1100, Ben Finney wrote:
> /dev/rob0 <rob0 at gmx.co.uk> writes:
>
> > You CAN have as many PTR records as you want on any name. 
> > However, it's unlikely to do anything useful.
>
> It can be quite useful, since machines can have multiple NICs
> on the same network (for redundancy, among other reasons) each 
> presenting a different IP address.

I thought we were talking about multiple PTRs on the same name. 
Different IP addresses would mean different in-addr.arpa names. It
sounds like you are talking about multiple identical PTR values, 
where the in-addr.arpa names differ.
-- 
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