Delegating a Subdomain of a Reverse-Mapping Zone

6.3.1 Problem

You want to delegate a subdomain of your reverse-mapping zone to a set of name servers.

6.3.2 Solution

Just as with a forward-mapping zone, add NS records to your reverse-mapping zone's data file delegating the subdomain to the name servers. For example, to delegate the 1.168.192.in-addr.arpa subdomain to the name servers ns1.baz.bar.example and ns2.foo.example, you'd add these two NS records to the 168.192.in-addr.arpa zone data file:

1.168.192.in-addr.arpa. IN NS ns1.baz.bar.example.
1.168.192.in-addr.arpa. IN NS ns2.foo.example.

6.3.3 Discussion

There's very little difference between delegating a subdomain of a forward-mapping zone and a subdomain of a reverse-mapping zone: you add NS records to the parent zone, specifying the name of the subdomain and the domain names of the name servers. Some of the labels in the subdomain's name are the octets in an IP address, but the name server doesn't care about that.

The correspondence between octets and labels causes problems if you use network or subnet masks that don't break on an octet boundary -- you end up with either multiple zones per network or subnet or multiple networks per zone. For more, see Recipes Section 6.4 and Section 6.5.

Oh, there is one difference in delegating reverse-mapping zones: glue A records are rarely necessary in reverse-mapping zones, since most people don't give their name servers names like ns1.1.168.192.in-addr.arpa.

6.3.4 See Also

Recipes Section 6.4 and Section 6.5, for delegating reverse mapping for networks with network or subnet masks that don't break on an octet boundary.