Some hints on DNS config? [part 2]

Barry Margolin barmar at alum.mit.edu
Thu Jul 14 03:31:33 UTC 2005


In article <db4kdg$2amb$1 at sf1.isc.org>,
 Kimi Ostro <kimimeister at gmail.com> wrote:

> I think this is the part that bit me the first time and for some
> reason cannot get my head around it, specifically configuration of the
> authoritative and caching services?
> Well I know how to configure each seperately, it is more the
> "interaction" between the authoritative and caching services? I cannot
> see where the cache slots in and who needs to know what.. Obviously
> masters need to know about slaves and vice versa, clients/resolvers
> need to know about nameservers.

The interaction is pretty simple.

When the server starts up, it loads all the master and slave zone files 
that are listed in its named.conf file, and becomes authoritative for 
them (assuming there are no errors detected in the files).

For slave zones, it periodically schedules refreshes, where it checks 
with the master server to see whether the SOA serial number has 
increased, and transfers a new copy of the zone if so.

It loads the root hints, which tells it how to process queries that 
aren't in zones it's authoritative for.  To update the root server list, 
it queries one of the servers in the hints for the current root NS 
records.

When a query comes in, the server checks whether it has the answer in 
its memory, which contains both the authoritative zones that it loaded 
and the cache that it has built up.  If so, it sends the answer to the 
client.

If not, and if the query requests recursion and the client is in its 
allow-recursion access list, it recurses starting with the most NS 
records that match the name in the request.  If it hasn't built up much 
of a cache yet, it may have to start all the way up with the root 
nameservers, but more often it will have something better (e.g. the 
nameserver for .com).  When it recurses, it caches the responses so it 
can answer future queries more easily.

There are a few details I've glossed over, but that's most of what you 
need to understand when configuring BIND.  For more details, I suggest 
you get the book "DNS & BIND".

-- 
Barry Margolin, barmar at alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***



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