[enum-wg] Tier-2 provisioning: NS vs CNAME/DNAME

Hello ENUMmers,

I'm about to become responsible for a Tier-2 ENUM registry, part of the 
Irish ENUM
Trial.  I expect to use BIND as the name server platform for this 
purpose.  I have
supposed (perhaps naïvely) that the conventional delegation mechanism, 
using NS
records in the parent zone, would be appropriate.  This involves 
creating a new
zone as each new telephone number is registered, and configuring the 
zone specifically
on each of Tier-2 name servers.

I'm not sure I really want to buy in to this level of per-number 
provisioning
activity, and see apparently significant advantages in using the 
technique of RFC2317
(Classless IN-ADDR.ARPA delegation) to make life simpler.

The advantages I see are the following.

The Tier-1 zone file becomes smaller, with just one CNAME (or DNAME) 
record per
delegation, rather than two or more NS records.

At Tier 2, the named configuration file needs only per-server, rather 
than per-number-
per-server provisioning activity, and propagation of newly-registered 
numbers is driven
by NOTIFY rather than by reloading the updated configuration file on 
each server.

This looks like the way to go, but perhaps I'm missing something ?

Best regards,

Niall O'Reilly
UCD Computing Services