Robert Wessel robertwessel2 at
Thu Jan 29 22:48:23 UTC 2004

Michele Chubirka <chubirka at> wrote in message news:<bvbna8$11e$1 at>...
> Does the TTL of the A record which the CNAME points to, override any TTL set
> for a CNAME record? For example, if I set an A record's TTL for 60 seconds,
> but then have a CNAME which points to it with a TTL of 30 seconds, how long
> will the TTL actually be for that CNAME record?

The TTL for the CNAME and the A records are quite independent.  A
resolver or caching DNS server that gets a 30s CNAME and the 60s A
will, as expected, discard the CNAME after 30 seconds and the A after
60 (or earlier, as the mood strikes it).  If a second request for the
same name arrives after, say, 45 seconds, the resolver will refetch
whatever lead to the CNAME (which might, of course result in something
different), but if it points to the same A record, it can use the
still cached one.

A somewhat interesting case occurs when the CNAME and the A are both
returned on the query (which often happens if the two records are
coming from the same DNS server), in which case the "new" A record
should replace the "old" cached one, event though the hasn't
expired yet.

> Michele Chubirka
> Unix Systems Engineer
> George Washington University
> xxx-xxx-xxxx

Do you *really* want to be posting your phone number on USENET?

More information about the bind-users mailing list