PTR Configuration Question

[Mark Pettit]

>On Tue, Nov 30, 2004 at 11:52:50PM -0800,
> Yann Debonne <bind9-users at debonne.net> wrote 
> a message of 23 lines which said:
>
>> So, what is that "80" digit, and how did it enter the picture?!

To answer your question, Yann, they did that because the only way they
can delegate control over the PTR records for a subnet of size less
than /24 is to do something like what they set out in RFC2317.  They
delegate the subdomain "80.54.122.67.in-addr.arpa." to your three
nameservers, and then create CNAMEs that point to entries in the
delegated subdomain.

>It comes from the upper zone (probably your ISP).
>
>~ % dig +short 54.122.67.in-addr.arpa NS
>ns1.pbi.net.
>ns2.pbi.net.
>
>~ % dig +short @ns1.pbi.net -x 67.122.54.85
>85.80.54.122.67.in-addr.arpa.
>   ^^
>   They've apparently read RFC 2317 "Classless IN-ADDR.ARPA
>   delegation" in a very creative and unusual way.

I'm not sure why you consider it "very creative and unusual".  SBC
follows the method set out in section 4. fairly precisely.  The only
thing they leave off is the netmask specification.

So instead of

  $ORIGIN 54.122.67.in-addr.arpa.
  80/29   NS      gate.debonne.net.
  80/29   NS      milk.purecreamery.com.
  80/29   NS      wall.softplanners.com.
  80/29   NS      ns1.pbi.net.
  80/29   NS      ns2.pbi.net
  81      CNAME   81.80/29
  82      CNAME   82.80/29
  83      CNAME   83.80/29
  84      CNAME   84.80/29
  85      CNAME   85.80/29
  86      CNAME   86.80/29

They chose to do this:

  $ORIGIN 54.122.67.in-addr.arpa.
  80      NS      gate.debonne.net.
  80      NS      milk.purecreamery.com.
  80      NS      wall.softplanners.com.
  80      NS      gate.debonne.net.
  80      NS      gate.debonne.net.
  81      CNAME   81.80
  82      CNAME   82.80
  83      CNAME   83.80
  84      CNAME   84.80
  85      CNAME   85.80
  86      CNAME   86.80

-- 
Mark K. Pettit
pettit at yahoo-inc.com