Olaf Kirch - Linux Network Administrator Guide, Second Edition

named is usually started at system boot time and runs until the machine goes down again. Implementations of BIND prior to Version 8 take their information from a configuration file called /etc/named.boot and various files that map domain names to addresses. The latter are called zone files . Versions of BIND from Version 8 onwards use /etc/named.conf in place of /etc/named.boot .

To run named at the prompt, enter:

# /usr/sbin/named

named will come up and read the named.boot file and any zone files specified therein. It writes its process ID to /var/run/named.pid in ASCII, downloads any zone files from primary servers, if necessary, and starts listening on port 53 for DNS queries.

The BIND configuration file prior to Version 8 was very simple in structure. BIND Version 8 has a very different configuration file syntax to deal with many of the new features introduced. The name of the configuration file changed from /etc/named.boot , in older versions of BIND, to /etc/named.conf in BIND Version 8. We'll focus on configuring the older version because it is probably what most distributions are still using, but we'll present an equivalent named.conf to illustrate the differences, and we'll talk about how to convert the old format into the new one.

The named.boot file is generally small and contains little but pointers to master files containing zone information and pointers to other name servers. Comments in the boot file start with the (#) or (;) characters and extend to the next newline. Before we discuss the format of named.boot in more detail, we will take a look at the sample file for vlager given in Example 6.8.

Example 6.8: The named.boot File for vlager

;

; /etc/named.boot file for vlager.vbrew.com

;

directory /var/named

;

; domain file

;____________________

cache . named.ca

primary vbrew.com named.hosts

primary 0.0.127.in-addr.arpa named.local

primary 16.172.in-addr.arpa named.rev

Let's look at each statement individually. The directory keyword tells named that all filenames referred to later in this file, zone files for example, are located in the /var/named directory. This saves a little typing.

The primary keyword shown in this example loads information into named. This information is taken from the master files specified as the last of the parameters. These files represent DNS resource records, which we will look at next.

In this example, we configured named as the primary name server for three domains, as indicated by the three primary statements. The first of these statements instructs named to act as a primary server for vbrew.com , taking the zone data from the file named.hosts .

The cache keyword is very special and should be present on virtually all machines running a name server. It instructs named to enable its cache and to load the root name server hints from the cache file specified ( named.ca in our example). We will come back to the name server hints in the following list.

Here's a list of the most important options you can use in named.boot :

directory

This option specifies a directory in which zone files reside. Names of files in other options may be given relative to this directory. Several directories may be specified by repeatedly using directory . The Linux file system standard suggests this should be /var/named .

primary

This option takes a domain name and filename as an argument, declaring the local server authoritative for the named domain. As a primary server, named loads the zone information from the given master file.

There will always be at least one primary entry in every boot file used for reverse mapping of network 127.0.0.0 , which is the local loopback network.

secondary

This statement takes a domain name, an address list, and a filename as an argument. It declares the local server a secondary master server for the specified domain.

A secondary server holds authoritative data on the domain, too, but it doesn't gather it from files; instead, it tries to download it from the primary server. The IP address of at least one primary server thus must be given to named in the address list. The local server contacts each of them in turn until it successfully transfers the zone database, which is then stored in the backup file given as the third argument. If none of the primary servers responds, the zone data is retrieved from the backup file instead.

named then attempts to refresh the zone data at regular intervals. This process is explained later in connection with the SOA resource record type.

cache

This option takes a domain name and filename as arguments. This file contains the root server hints, which is a list of records pointing to the root name servers. Only NS and A records will be recognized. The domain should be the root domain name, a simple period (.).

This information is absolutely crucial to named; if the cache statement does not occur in the boot file, named will not develop a local cache at all. This situation/lack of development will severely degrade performance and increase network load if the next server queried is not on the local net. Moreover, named will not be able to reach any root name servers, and thus won't resolve any addresses except those it is authoritative for. An exception from this rule involves forwarding servers (see the forwarders option that follows).

forwarders

This statement takes a whitespace-separated list of addresses as an argument. The IP addresses in this list specify a list of name servers that named may query if it fails to resolve a query from its local cache. They are tried in order until one of them responds to the query. Typically, you would use the name server of your network provider or another well-known server as a forwarder.

slave

This statement makes the name server a slave server. It never performs recursive queries itself, but only forwards them to servers specified in the forwarders statement.

There are two options that we will not describe here: sortlist and domain . Two other directives may also be used inside these database files: $INCLUDE and $ORIGIN . Since they are rarely needed, we will not describe them here, either.

BIND Version 8 introduced a range of new features, and with these came a new configuration file syntax. The named.boot , with its simple single line statements, was replaced by the named.conf file, with a syntax like that of gated and resembling C source syntax.

The new syntax is more complex, but fortunately a tool has been provided that automates conversion from the old syntax to the new syntax. In the BIND 8 source package, a perl program called named-bootconf.pl is provided that will read your existing named.boot file from stdin and convert it into the equivalent named.conf format on stdout. To use it, you must have the perl interpreter installed.

You should use the script somewhat like this:

# cd /etc

# named-bootconf.pl ‹named.boot ›named.conf

The script then produces a named.conf that looks like that shown in Example 6.9. We've cleaned out a few of the helpful comments the script includes to help show the almost direct relationship between the old and the new syntax.