Secondary for reverse CIDR delegation (whew!)

[Barry Margolin]

In article <a6to23$htq at pub3.rc.vix.com>,
Damon LaCaille <lacaille at pobox.com> wrote:
>
>How would one go about setting up a DNS server that acts as a
>secondary for a non-octet reverse delegation?
>
>For example:  I am company.com, and my isp hands me 1.2.3.0/25 so I
>have 128 addresses 1.2.3.0 through 1.2.3.127.
>
>My primary DNS server acts as the authority for these through the
>CNAME that the RFC recommends using.  However, how does may secondary
>DNS server know which IP addresses are active and which are not for
>zone transfers of that CIDR block?  I can't tell it to download the
>whole 1.2.3.0/24 zone because I only own half of it, and I can't tell
>it to download the individual IP addresses because the secondary
>wouldn't know which IP addresses are active and which aren't.  Make
>sense?

The name of the zone that's delegated to you is presumably something like
0/25.3.2.1.in-addr.arpa.  So if you have

zone "0/25.3.2.1.in-addr.arpa" {
  type master;
  ... };

in your configuration, the secondary should have:

zone "0/25.3.2.1.in-addr.arpa" {
  type slave;
  masters { <your address>; };
  ... };


>The RFC only explains how to set up a primary reverse resolution name
>server for CIDR, not a secondary from what I can tell.

The only thing special about these domains is the content and the CNAMEs in
the parent.  When setting up a slave server, none of that is relevant, so
there's nothing to explain.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Woburn, MA
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