[SURBL-Discuss] TTL/turnaround times for SURBL

Patrik Nilsson patrik at patrik.com
Tue Aug 3 21:32:26 CEST 2004


At 02:50 2004-08-03 -0700, Jeff Chan wrote:
>I think that would be done by lowering the TTL.  The
>time to live appears to indicated to DNS how quickly
>new information should be served up.  Do any DNS gurus
>know if that's correct?  In other words if we lower the
>TTLs on our zone files should we expect new entries
>to be visible sooner.

If you are using version 9 of Bind, the positive TTL is set by the $TTL 
directive for the zone, unless there is a specific TTL for the RR, in which 
case that is used.

Negative TTLs (for NXDOMAIN/"not found" replies) are set by the "minimum" 
SOA directive.

This "negative caching time" use of the miminum directive is specific to 
Bind 9 though. Earlier versions of Bind and most other name servers treat 
it as a default miminum TTL in general.

For rbldnsd, it might be possible to do something similar using the soa ttl 
value for negative and the $ttl directive for positive replies, but I am 
not sure.

> > Finally, has any progress been made
> > speeding up the refresh times for
> > multi.surbl.org?
>
>It's certainly something that can be done rather easily
>but I'd like to get some feedback about the impact on
>our nameservers as a result.  Do shorter TTLs mean
>more DNS traffic?  Does it cause positive caches to
>expire sooner and therefore cause more querying of
>authoritative name servers?

At least in theory, with Bind 9, negative and positive caching can be set 
separately.

Try lowering the 8H 'minimum' value for multi.surbl.org while keeping the 
8H RR TTL or zone $TTL value.

Patrik 



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