low TTL on cache NS

[Kevin Darcy]

dave stern wrote:

>I have several mailservers running cache-only nameservice to reduce
>their
>external queries. On occasion, we move hosts from one net to another but
>the
>Cache-only NS doesn't pick  up the IP change we make on the master NS
>despite the mailserver being listed in the named.conf on the master
>under
>also-notify.
>
>Is there a way to reduce the TTL on cache-only NS to something really
>small?
>
>I'm guessing that the Cache-only NS inherits the TTL from the master
>anyway
>thus making a change to its named.local for a short, default TTL wont
>work.
>
>Thinking out loud, I could accomplish the same thing by just having a
>cronjob
>on the Cache-only NS to reload every hour. OTOH, I doubt this is even a
>wise thing to do as
>- We generate and push/pull host files nightly so the current file
>wouldn't have the
>   update anyway
>- Reloading frequently defeats the purpose of running NS on the
>mailserver
>
>Thoughts? ideas?opinions?
>
NOTIFY is only used between masters and slaves, so it won't have any 
effect on a caching nameserver.

Why don't you temporarily lower the TTL on the records that you know are 
going to change? You _could_, theoretically, tune your caching 
nameservers to expire things quickly out of their caches, sure, but then 
it would be doing that for *everything*, *all* of the time, thrashing 
around constantly having to re-fetch data that the authoritative 
nameservers for the relevant zones didn't think would have expired 
already. Do you really want all of that traffic and 
resource-consumption? Seems more reasonable to be selective about the 
caching that one defeats...

- Kevin