How to do I do reverse on a Supernet?

[Barry Margolin]

In article <Pine.OSF.3.96.990721153511.4653A-100000 at firma.thezone.net>,
Roderick B. Greening <roderick at cableatlantic.nf.ca> wrote:
>On Wed, 21 Jul 1999, Berislav Todorovic wrote:
>
>> In article <Pine.OSF.3.96.990721132916.5303K-100000 at firma.thezone.net>,
>>   "Roderick B. Greening" <roderick at cableatlantic.nf.ca> wrote:
>> > But RFC 2317 does not cover shorter prefixes like /23, /22, or /21?
>> 
>> For prefixes shorter than /24, but lonter than /16 you can:
>
>	The problem is that we have a supernet (/22) which has a forward
>	domain my-domain-here.net. The forward is updated via dynamic DNS
>	(Network Registrar sends DDNS updates to our server). The reverse
>	would work, but we have to specify a single zone to send reverse
>	updates to. Since there are other /24's in the main /16, we can
>	not put it in a single file (the /24's have their own zone for 
>	other customers). How do we generate a zone for the /22 which can
>	be updated via DDNS from Network Registrar?

One way to do it would be to direct the updates to the /16 zone.  You can
still delegate individual /24's out of this zone as well.

Another way would be to adapt the principles of RFC 2317.  Suppose you're
doing DDNS for x.y.20.0/22.  In the y.x.in-addr.arpa zone file, put:

20/22 IN NS ddns-server.company.com.

$GENERATE 0-255 $.20 IN CNAME $.20.20/22
$GENERATE 0-255 $.21 IN CNAME $.21.20/22
$GENERATE 0-255 $.22 IN CNAME $.22.20/22
$GENERATE 0-255 $.23 IN CNAME $.23.20/22

However, without knowing more about the DDNS client, I'm not sure whether
you can get it to send the appropriate dynamic updates for this zone.  For
a machine with IP address x.y.z.w it would have to update the PTR record
for w.z in the 20/22.y.x.in-addr.arpa zone.

-- 
Barry Margolin, barmar at bbnplanet.com
GTE Internetworking, Powered by BBN, Burlington, MA
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