Delegating in-addr.arpa for subnetted address space

[mike at bilow.com (Michael Bilow)]

You cannot do this.  From the perspective of DNS, reverses are treated as
strings of components separated by dots.  As a result, you can only do a
delegation of a reverse on an octet boundary.

For example, if you have an IP address such as 1.2.3.4, then its reverse
will be handled by a zone that is authoritative on an octet boundary, and
there are only four possibilities:

	1.in-addr.arpa
	2.1.in-addr.arpa
	3.2.1.in-addr.arpa
	4.3.2.1.in-addr.arpa

It is this last possibility which should give you a clue as to the
solution.  Assuming that your ISP has a zone of authority for your larger
enclosing CIDR block, then they need to delegate each one of the 16
addresses to your name server.  They would do it something like this:

	$ORIGIN 3.2.1.in-addr.arpa.
	* * *
	16	NS	ns.thorin.com.
	17	NS	ns.thorin.com.
	18	NS	ns.thorin.com.
	19	NS	ns.thorin.com.
	20	NS	ns.thorin.com.
	21	NS	ns.thorin.com.
	22	NS	ns.thorin.com.
	23	NS	ns.thorin.com.
	24	NS	ns.thorin.com.
	25	NS	ns.thorin.com.
	26	NS	ns.thorin.com.
	27	NS	ns.thorin.com.
	28	NS	ns.thorin.com.
	29	NS	ns.thorin.com.
	30	NS	ns.thorin.com.
	31	NS	ns.thorin.com.

Strictly speaking, you would need a separate zone file for each one of
these addresses, since technically each address is in its own zone.  You
could fake this and use a single zone file if you did not mind hiding and
being unable to reverse the IP addresses of your neighbors yourself.

-- Mike


On 2001-07-12 at 23:30 -0400, thorin wrote:

> Have a quick question and I hope someone Can point me in the right
> direction.
> 
> My ISP has allocated a /28 (255.255.255.240 - 16 addresses) for my use
> here.
> Forward lookups work like a charm and are replicating to the slaves as
> planned.
> 
> However, I have the need for reverse lookups to resolve and was
> wondering if anyone has tackled this before in a subnetted environment.
> I'm assuming I'll have to call my ISP (UUNet) and ask them to delegate
> my portion of the address space before any of my modifications will take
> effect - but I want to make sure I'm not missing something obvious here.
> 
> --Thorin


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