Classless in-addr.arpa delegation

Why

Many enterprises are joining the net

Size frequently does not justify /24 prefix

Desire to assign < /24 prefix

Problem delegating in-addr.arpa authority because in-addr.arpa mechanism is octet-oriented

The problem

Enterprise A has 192.0.2.0/27

Enterprise B has 192.0.2.32/28

Who maintains
2.0.192.in-addr.arpa?

Approach 1

Have 2.0.192.in-addr.arpa maintained by central body (e.g. service provider)

Maintainer must be notified of every change

Delays in processing

Does not scale

CNAME

CNAME can be used to ‘move’ objects in the DNS tree:
www.foo.com CNAME server.isp.net

Can use CNAME to alias parts of
in-addr tree

Normal delegation

$ORIGIN	2.0.192.in-addr.arpa.
1	PTR	pc1.other.domain.
2	PTR	pc2.other.domain.
...

Approach 2

$ORIGIN	2.0.192.in-addr.arpa.
0	CNAME	0.some.domain.
1	CNAME	1.some.domain.
2	CNAME	2.some.domain.
…

32	CNAME	32.other.domain.
33	CNAME	33.other.domain.

$ORIGIN	some.domain.
1	PTR	pc1.some.domain.

Moving PTR records to different zones

Can point CNAME records to other places in domain tree:

in-addr.arpa.some.domain

0/27.2.0.192.in-addr.arpa

0-27.2.0.192.in-addr.arpa

Comments

Need to add (a lot of) CNAME records in 2.0.192.in-addr.arpa
This is normal

This is not hard, it is confusing

domain names may be confusing

Documentation

See RFC2317 for documentation
(it’s not a tutorial, however)

See ‘DNS and BIND’ page 214 onwards

Classless in-addr.arpa delegation

ymbk

2000-05-02T05:54:26