Domain names are assigned through a registration process with one of the domain name registrars available on the Internet (http://www.internic.net/regist.html). Originally, a single authority managed domain names. As commercial uses for domain names spread, additional entities sought the ability to charge for the service of domain registration, and today there are a number of qualified registrars (a search for domain registrar on one of the popular search engines will yield a daunting list). Once a domain name is registered, it is listed in a worldwide database along with contact information for the owners or their agents. The name servers that contain DNS information for the domain can go along with this record.

Most registrants offer a domain name search service, so you can test desired domain names for availability. If the domain name you're seeking is available, you can provide payment information to a registrant and purchase rights to use the name, usually for one or two years.

named is often configured to serve DNS requests even when it does not have local information for a domain. Instead, it is used for its caching ability. When a client program requests an address resolution from the local named, the daemon first checks its local cache. If it doesn't find the domain there, it goes to other DNS servers as usual. If the cache does contain the domain, it is returned immediately to the client from the cache, which speeds the resolution process.

Some Linux distributions come with a caching-only named configuration pre-installed. If this isn't the case for you, simply follow the brief instructions in Section 3 of the DNS HOWTO available from http://www.tldp.org. Part of the configuration includes setting your local system as the default DNS server in /etc/resolv.conf:

nameserver 127.0.0.1

You can test the configuration using the nslookup utility:

# nslookup
Default Server:  localhost
Address:  127.0.0.1
> lpi.org
Server:  localhost
Address:  127.0.0.1
Name:    lpi.org
Address:  209.167.177.93
> lpi.org
Server:  localhost
Address:  127.0.0.1
Non-authoritative answer:
Name:    lpi.org
Address:  209.167.177.93
> exit

In this example, nslookup attaches to the default server localhost (127.0.0.1). In the first query for lpi.org, the local named must find the address from external DNS servers. However, the result is found in the cache on the second try, as indicated by the Non-authoritative answer response. If this behavior isn't seen, there may be a problem with the named configuration in /etc/named.conf.

Some debugging information can be found in /var/log/messages. For example, the bold line in this short excerpt shows an error in the configuration file:

smp named[216]: starting.  named
smp named[216]: cache zone "" (IN) loaded (serial 0)
smp named[216]: Zone "0.0.127.in-addr.arpa"
  (file named.local): No default TTL
  set using SOA minimum instead
smp named[216]: master zone "0.0.127.in-addr.arpa"
  (IN) loaded (serial 1997022700)
smp named[216]: /etc/named.conf:18: can't redefine
channel 'default_syslog'
smp named[216]: listening on [127.0.0.1].53 (lo)
smp named[216]: listening on [192.168.1.30].53 (eth0)
smp named[216]: Forwarding source address is [0.0.0.0].1855
smp named[216]: Ready to answer queries.

Note that configuration of a caching-only name server is beyond the scope of the LPIC Level 1 Exams but is a useful exercise in understanding the configuration of named.

A few tools exist to verify the operation of DNS name resolution. Here's a brief synopsis of nslookup and host, both specifically mentioned in this Objective. The host utility does not offer interactive mode but uses a syntax similar to nslookup.

It's likely that a Linux administrator will maintain or install systems running BIND v4.x as well as the newer v8.x. This LPI Objective requires an understanding of the differences between the configuration files for these two BIND versions. Under BIND v4, the configuration file was called /etc/named.boot. Example 20-6 shows a trivial BIND v4 configuration file.

directory                                /var/named
cache   .                                root.hints
primary 0.0.127.IN-ADDR.ARPA             127.0.0.zone
primary localhost                        localhost.zone

In BIND v8, the configuration file was renamed /etc/named.conf. Example 20-7 shows the equivalent configuration in the BIND v8 format.

options {
        directory "/var/named";
};
zone "." {
        type hint;
        file "root.hints";
};
zone "0.0.127.IN-ADDR.ARPA" {
        type master;
        file "127.0.0.zone";
};
zone "localhost" {
        type master;
        file "localhost.zone";
};

As you can see, the information contained in the files is largely the same, but the v8 format contains a more formal structure. For those upgrading to Version 8, the Perl script named-bootconf.pl is included in the v8 package to upgrade named.boot to named.conf.