Common BIND Files
Introduction
So far we
have covered in great detail the main files required
for the space.net domain. These files, which we
named db.space.net and db.192.168.0, define all the
resouce records and hosts available in the space.net
domain.
Now, even
though the contents of these files are common for
every domain but vary in their contents (e.g
resource records defined for each domain), there are
some files that are common and have pretty much the
same contents for any type of domain !
We will be
looking at these files on this page and analysing
them to help you understand why they exist and how
they fit into the big picture :)
Our Common Files
There are
3 common files that we're going to look at. However,
the first two files'
contents change slightly depending on the domain,
this is because they must be aware of the various
hosts and the domain name for which they are
created. The third file
is always the same amongst all DNS servers and I'll
explain more about it later on.
So here
are our files:
-
named.local or
db.127.0.0
-
named.conf (analysed
at the end)
-
named.ca or
db.cache
We are
going to take each file and look at its contents,
this will make them easier to understand.
The named.local File
The
named.local file, or db.127.0.0 as some might call
it, is used to cover the loopback network. Since no
one was given the responsibility for the 127.0.0.0
network, we need this file to make sure there are no
errors when the DNS server needs to direct traffic
to itself (127.0.0.1 IP Address - Loopback).
When
installing BIND, you will find this file in your
caching example directory: /var/named/caching-example,
so you can either create a new one or modify the
existing one to meet your requirements.
The
file is no different than our example db.addr file
we saw previously:
$TTL 3h
0.0.127.in-addr.arpa. IN SOA voyager.space.net.
admin.space.net. (
1 ; Serial
3h ; Refresh after 3 hours
1h ; Retry after 1 hour
1w ; Expire after 1 week
1h ) ; Negative caching TTL of 1
hour
0.0.127.in-addr.arpa. IN NS voyager.space.net.
0.0.127.in-addr.arpa. IN NS gateway.space.net.
1.0.0.127.in-addr.arpa. IN PTR localhost.
That's
all there is for named.local file !
The named.ca File
The
named.ca file (also known as the "root hints file")
is created when you install BIND and dosen't need to
be modified unless you have an old version of BIND
or it's been a while since you installed BIND.
The
purpose of this file is to let your DNS server know
about the ROOT Servers on the Internet. There is no
point showing the whole content of this file because
it's quite big, so I'll show you an entry of a ROOT
server so you can see what it looks like:
; last update: Aug 22,
1997
; related version of root zone: 1997082200
;
;
; formerly NS.INTERNIC.NET
;
. 3600000 IN NS A.ROOT-SERVERS.NET.
A.ROOT-SERVERS.NET. 3600000 A 198.41.0.4
The domain
name "." refers to the
root zone and the "3600000"
is an explicit time to live for the records in the
file, but it is generally ignored :) The rest are
self explanatory. If you want to grab a new copy of
the root hint file you can ftp to
ftp.rs.internic.net (198.41.0.6)
and log on anonymously, there you will find the
latest up to date version.
The named.conf File
The
named.conf file is usually located in the /etc
directory and is the key file that ties all the zone
data files together and lets the DNS server know
where they are located in the system. This file is
automatically created during the installation but
you must edit it in order to add new entries that
will point to any new zone files you have created.
Let's have
a close look at the named.conf file and explain:
options {
directory "/var/named";
};
// Root Servers
zone "." IN {
type hint;
file "named.ca";
};
// Entry for Space.net - name to ip mapping
zone "space.net" IN {
type master;
file "db.space.net";
};
// Entry for Space.net - ip to name mapping
zone "0.168.192.in-addr.arpa" IN {
type master;
file "db.192.168.0";
};
// Entry for Local Loopback
zone "0.0.127.in-addr.arpa" IN {
type master;
file "named.local";
};
At
first glance it might seem a maze, but it's a lot
simpler than you think. Break down each paragraph
and you can see clearly the pattern that follows.
Starting from the top, the options section simply
defines the directory where all the files to follow
are located, the rest are simply comments.
The
root servers section tells the DNS server where to
find the root hints file, which contains all the
root servers. Next up is the entry for our domain
space.net, we let the DNS server know which file
contains all the zone entries for this domain and
let it know that it will act as a master DNS server
for the domain. The same applies for the entry to
follow, which contains the IP to Name mappings, this
is the 0.168.192.in-addr.arpa
zone.
The
last entry is required for the local loopback. We
tell the DNS server which file contains the local
loopback entries.
Notice
the "IN" class that is
present in each section ? If we accidentally forgot
to include it in our zone files, it wouldn't matter
because the DNS server will automatically figure out
the class from our named.conf file. It's imperative
not to forget the "IN"
(Internet) class in the named.conf, whereas it
really doesnt matter if you don't put it in the zone
files. It's good practice still to enter it in the
zone files as we did, just to make sure you don't
have any problems later on.
And
that ends our discussion for the common DNS (BIND)
files. Next up is the configuration of our
Slave/Secondary DNS server.
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