I don't understand why you need this to happen every 5 minutes. If it is delegations are from the root servers, they are only updated twice daily. Sure you can update the zone files right after the registration, but nobody except people who use your name servers for recursive lookups will get that info.
If the problem is more one of pleasing the customer than doing the technically sufficient thing, I suggest the following: Separate the authoritative servers (A) from the ones the customers use for recursive lookups (R). Add the _new registrations_ to the R servers and update R's every five minutes. The customers who use the R servers will get the 'right' answers and be happy. Twice a day, yank that day's batch of new zones from the R servers and move them to A servers. This way R servers get updated often but with 100-500 zone files, the A servers get updated just in time. If the customers grab the DNS IP's via PPP, you can change the numbers very easily. Would this work, or am I misunderstaning the problem? cheers, BM
