network change

[Kevin Darcy]

Eric A. Hall wrote:

> > When we had the first network move to the current provider, we had
> > trouble with DNS. People for outside our network had difficulty
> > connecting to certain site because the old DNS data was still being
> > looked up. I'm wondering if any of you have a better solution and
> > perhaps can give me advise.
>
> The data was probably stuck in various caches. You have two options on
> your next changeover. The first one is to start shortening the TTL
> values of your DNS data so that it does not get cached for as long. By
> the time you get ready for your changeover, have the TTL down to 30
> minutes or some other small value so that the data expires quickly. You
> will still have some problems but not that many and not for very long.
> You will need to time this right, as you don't want to have queries
> being answered with TTL of 2 weeks the day before the transition.

> Another option is to run both networks simultaneously and gradually
> migrate the DNS pointers to the new addresses. Harder but definitely a
> smoother way to transition.

Shortening the TTL's on your own records is all very well and fine, but
what about the TTL's on the TLD server's glue records? These are typically
2 days. To deal with that issue, it may be wise to add new delegations
pointing to the new addresses of the nameservers, assuming you know those
addresses in advance. Then delete the old delegations after the migration
is complete. Unfortunately, with this approach, since InterNIC forbids
multiple names for the same address, or multiple addresses associated with
a name in their "host" records, you'll have to either give your
nameservers different names permanently, or, after the move, migrate them
back to their original names through a series of incremental host-record
updates.


- Kevin