Primary or cache DNS

[Kevin Darcy]

cpalom wrote:

> Newbie question
> How can I know which of the 2 DNS server in my office is a Primary and which
> one is cache, is there any special setting that I should look for ?

A primary will always answer authoritatively, a caching server may sometimes
answer non-authoritatively, if the answer comes from its cache rather than from
an authoritative source. So a common way of checking is just query the server
twice in quick succession; if it's a caching server, the second answer will
almost certainly be from the cache, and therefore marked as non-authoritative.
The only exception would be if the TTL (time to live) of the record(s) you are
querying is very low (e.g. 0), then the record is cached for only a very short
time, or not at all, and it may not be possible to catch a caching server
"red-handed" giving a non-authoritative answer.

By the way, how do you know that the non-primary server in your office is a
caching server? It might be a slave. In this case, it will always answer
authoritatively and there is no reliable way of remotely telling it from the
primary.

Just out of curiosity, why do you care? Pick the fastest and/or more reliable
server; whether it's "primary" or not is mostly irrelevant.


- Kevin