Can name servers ignore TTLs?

Answered Wed, 5 Jun 2002

> I ran into an interesting situation during a host DNS change at a major
> University in New York this weekend. The master DNS server has a TTL for
> the domain of 60 minutes. I confirmed the actual time of DNS change by
> direct nslookup polls of the primary every few minutes last Friday
> evening. I got reports from users that the host in question was
> inaccessible for almost 2 days following by some off campus users. I
> verified it was stale data by having some users swap the new IP number of
> the host name into their URL's.
>
> I have heard discussions that major ISP's have a method of ignoring the
> TTL handed out by an authoritative name server in their caches. I
> rummaged through my copy of DNS and Bind (second edition) and could find
> nothing on this topic. Is there any truth to this? Or is there some
> other mechanism at work?

There's no mechanism within a plain vanilla BIND name server to do this, but I've heard that some service providers employ special name servers that place a minimum TTL on cached data.

There are a couple of other possibilities, too: Older browsers cache
name-to-address mappings indefinitely. Also, if the domain name of
the host is registered on the gTLD name servers, it can stay there--
and stale--indefinitely.

cricket