DNS TTLs revisited

Barry Margolin barmar at alum.mit.edu
Fri Feb 6 00:02:01 UTC 2004


In article <bvuho7$2ath$1 at sf1.isc.org>, Robert Gahl <bgahl at bawcsa.org> 
wrote:

> Thus my question: Do earlier versions of BIND lack the ability to recognize 
> the specific setting of TTLs on individual hosts?

This is a meaningless question.  That's the *only* place that TTLs 
exist.  If they didn't recognize this, they wouldn't recognize TTLs at 
all, since there are no other TTLs to recognize.

The "default TTL" of the zone is not communicated at all in the DNS 
protocol, it's only a syntactic convenience used when named parses the 
zone file.  There's absolutely no way for a client of the server to tell 
the difference between explicit per-record TTLs and TTLs inherited from 
the default.

Are you sure that your changes have propagated to all your slave 
servers?  And how long after you changed the TTL on the record did you 
do your tests?  If it was less than the old TTL, then you're just seeing 
records that are still in the caches, because the old TTL allowed them 
to stay around for a day.

-- 
Barry Margolin, barmar at alum.mit.edu
Arlington, MA


More information about the bind-users mailing list