How many nameservers?

[Chris Thompson]

On Feb 2 2009, shulkae wrote:

>How may NS entries typically is allowed per zone? Is there a bind
>limit or does it cause any side effects if the
>slaves are geographically distributed ?
>
>We would like to setup one zone for my new group who have offices all
>over the world ? We are planning
>to use BIND 9 over FreeBSD. There may be few SUN/Solaris hosts as
>well.
>
>We would like to start with around 16 Slaves per master per zone. Is
>this too much? My tests did not reveal any side effect fortunately.
>
>Anyone with experience of setting up DNS slaves all around the globe
>please advise..

The questions "how many NS records?" and "how many slaves?" are not
the same. You should consider stealth slaving (q.v.) on your local
recursive nameservers.

If you are talking about DNS domains connected to the outside world,
then the NS records are not primarily for your benefit: they are for
the outside world. So they should all refer to hosts with decent
external Internet access (and yes, they should be "geographically
distributed" if possible). That doesn't apply to stealth slaves.

I suspect that BIND's RTT-based balancing of queries to the hosts
referenced in multiple NS records wouldn't gain anything from as
many as 16 of them, and it could even be counter-productive. "Maximum
of seven" used to be a rule of thumb, although that was at least 
partly based on the no-longer-entirely-relevant 512-byte limit
mentioned in other postings.

RFC 2182, "Selection and Operation of Secondary DNS Servers",
although 11.5 years old, is still very much worth reading.

-- 
Chris Thompson
Email: cet1 at cam.ac.uk