Cisco Distributed Director

[Werner Wiethege]

On Fri, 16 Jun 2000, Barry Margolin wrote:
 
> Since your TTL is 0 seconds, the caching nameserver shouldn't actually
> cache the record.  It should forward it to the client machine, and then
> discard it.  The next time a client tries to look it up, the caching server
> should go back to the DD.  If you have even load balancing configured on
> the DD, it should alternate which address it gives out each time.  AFAIK,
> the fact that all the queries are coming from the same nameserver shouldn't
> matter.
 
The BIND 8.2.3T5B code checks for staleness of a record with the
following
comparison (in function stale in ns_eq.c):
                  dp->d_ttl >= (u_int32_t)tt.tv_sec               
where d_ttl is the time when a record expires and tv_sec the current
time.
I assume older versions have the same kind of check.
Considering records to be valid as long as the times in seconds are
the same can explain the behaviour that a caching nameserver keeps
returning the same value for almost a second when the TTL is 0.
Tests done by Pete Taylor where he left out without the equal sign
have shown different behaviour. Does TTL have inclusive or exclusive
interpretation in the standards or is it an implementation issue?
 
Werner