Extending dynamic address range w/ DDNS

[Frank Stanek]

Hello,

we have been assigned a /22 IP address range for internal use. Of this
range we have been using a /24 range for dynamic clients with DDNS
updates (dhcpd 3.0.3, BIND 9.4.3-P3), the other three /24 ranges are
currently reserved for static hosts and other things. On the BIND
side we have one static forward zone and one dynamic one. As for the
reverse zones we have four: one dynamic zone and three static ones (one
for each of the /24 ranges).

The relevant part of the dhcpd configuration looks like this:
subnet 172.16.0.0 netmask 255.255.252.0 {
    authoritative;
    range 172.16.2.0 172.16.2.255;
    default-lease-time 172800;
    max-lease-time 345600;
    zone dynamic.intern. { primary 127.0.0.1; key key_ddns; }
    zone 2.16.172.in-addr.arpa. { primary 127.0.0.1; key key_ddns; }
    allow unknown-clients;
# ...
}

Now this dynamic range is getting too small because of an increase
in the number of dynamic clients. We tried to extend the range like
this
range 172.16.1.30 172.16.2.255;
but then obviously only the 2.16.172.in-addr.arpa. zone will get updated,
not the 1.16.172.in-addr.arpa. zone. Adding the 1.16.172 zone does not
work because it seems dhcpd does not recognize which zone should be updated
based on the IP address it hands out. We have also tried to work with
classes or pools but the problem is we do not have a sensible way
by which to distinguish the clients, ie should a certain client
be in one or the other pool/class.

Another way might be to merge the two reverse zones into one. However
that would be pretty ugly because of the journal files. Also if we
did that, we would still have the two static reverse zones
0.16.172.in-addr.arpa. and 3.16.172.in-addr.arpa. while we would
now have a dynamic reverse zone 16.172.in-addr.arpa.. Not pretty.

Could anyone please give me some hints as to what is the "best"
way to increase the dynamic range without making the configuration
ugly or confusing?

Regards
Frank