TTL: does it really work?

[Kevin Darcy]

Michele Chubirka wrote:

> I'm having great difficulty with my zone data staying cached MUCH longer
> than my zone's default TTL. Is this common Or do I have bigger problems.
> Usually the issue comes up with large ISPs like UUnet.

You should verify that the records in question actually have the TTL's you
think they do. If for some reason you have a explicit TTLs in your zonefile
-- for whatever reason -- then maybe your default TTL is being overriden.

Another possibility is that the records in question are coming from the
TLD servers as "glue records". These typically have TTLs of 2 days or more.
Newer nameservers observe strict "data ranking" rules (see RFC 2181) and so
glue records will be discarded in favor of records which come directly from
authoritative servers. But not everyone is running up-to-date nameserver
software, and in any case, there may be situations where other people's
nameservers may get a glue record cached and not consider it necessary to
"upgrade" that record by asking your authoritative servers for them. The
moral of the story is your nameserver records shouldn't point to volatile
A records. Nameserver records hold the namespace together, so for them,
*persistence* is preferred.

Other than those caveats, yes, TTL really works. I use it all the time :-)


- Kevin