DNS (Domain name server/service)

DNS maps the host name (eg mail.earth.monash.edu.au) to an ip number (eg 130.194.168.8).

A DNS server provides this ability to clients and also defines all the machines under our control and provides this information to the world.

The server in our department only caches our local information and provides the mapping service to the clients.

ITS provides DNS data to the rest of the world for our department via the addhost service.

Packages

Under linux, following rpm's are required (for mandrake8.0).

bind-9.1.1-1mdk
bind-utils-9.1.1-1mdk

Hosts

DNS can run on a number of servers providing redundant service.

neo main server (local network connected)
orion old server (locally connected)
s2 server (is really neo)
s3 backup server (its network connected)
s4 ACRC server (in building 27)
virtual exporer ACRC server (virtualexplorer.[com|etc...])
bifrost cam's server (darkqueen.org)

Files

/etc/named.boot
WARNING: this is an old file that is refered to in the DNS book by oriley, but it is not used. DO NOT edit this file!
/etc/named.conf
This is the configuration file that defines what networks are known and where to look for names we do not know about.
/var/named/*
Files here contain information on IP and names that the server knows about.

Configuration

The named.conf file must be configured to know what files to look for in /var/named. A standard configuration file can be found in /Mount/config/data/Install/named/named.conf.

Config files for our department in /var/named/* are generated by host/machine database.

The most important part is the forwarders { 130.194.1.99; 130.194.7.99; }; line in the /etc/named.conf which tells our nameserver where to ask for hosts it doesnt know.

Problems...?

DNS should be reasonably stable because of the redundancy. The host/machine database should restart the service when it updates the config file.

You must be root to do the following.

sh /etc/rc.d/init.d/named status
sh /etc/rc.d/init.d/named stop
sh /etc/rc.d/init.d/named start

Changes not appearing...

You did make sure that you changed the serial number record in the SOA record? It must always go UP. NEVER DOWN!

named wont start...

Look in /var/log/messages for something like:

Jul 22 14:53:12 s2 named[2666]: dns_zone_load: zone 168.194.130.in-addr.arpa/IN: loading master file GEN.dns.168.rev: no ttl

Add: $TTL 172800 to the top of all the files in /var/named/GEN.*.

Checking...

You can check a dns server with:

dig @130.194.168.1 earth.monash.edu.au
Check dns on neo.
dig any @130.194.168.1 earth.monash.edu.au
Check SOA record on neo (notice serial number!).
dig mx @130.194.168.1 earth.monash.edu.au
Check mx (mail delivery order) on neo.