Classless delegation with a split horizon setup

[adhodgson at gmail.com]

Hi,

I am wondering whether any of you on the list can help me with a bit of
a DNS quandary I am in.

My ISP has given me an IP block 81.2.105.208/28.  I have to host PTR
records on my DNS server using the subnetted style
208-223.105.2.81.in-addr.arpa. - this is fine.  The ISP host the zone
105.2.81.in-addr.arpa (or most of it), and have created CNAME records
pointing to the subnetted zone, listing my public nameserver as the
primary for the subnetted zone.

However, I run a split horizon DNS setup with the public information on
one server and LAN-specific information on the other.  This is mainly
because our lan uses the subdomain ad.hodgsonfamily.org.  I host the
records on both on two completely different instances.

The issue I have is I want to create the reverse zone for inside my
LAN, but here I have an issue, as if I created 105.2.81.in-addr.arpa,
the rest of that zone (i.e, for IP addresses I don't own) are not being
resolved since the DNS server can pick up the zone locally.  If I
create the subnetted zone, there would be no CNAME records in the
parent to get resolution working.

Has anyone been in this situation before?  I have two possible
workarounds, one is to create a complete zone file for each IP address,
and the other involves ensuring only the subnetted zone exists, and
relying on resolution to find the cname records from the root
nameservers, thus when it gets to the looking up from the subnetted
zone it would know the information locally thus pick up the records?

Alternatively does anyone know a trick in bind I can use to get this
working a different (and probably more appealing!) way?

Thanks.
Andrew.