Reverse Zone

The reverse zones give you a hostname for every IP address assigned to that zone. Bob has decided that all IP address that are not currently used will have a name like bob123.bob.org. This is what the reverse zone would look like:

@		IN	NS	dns.bob.org.
$ORIGIN 2.1.IN-ADDR.ARPA.
3		IN	SOA	bob.org.	root.bob.org. (
			2001121401 ; serial
			10800 ; refresh
			3600 ; retry
			604800 ; expire
			86400 ; default_ttl
			)
3		IN	NS	dns.bob.org.
3		IN	NS	dns2.bob.org.
$ORIGIN 3.2.1.IN-ADDR.ARPA.
0		IN	PTR	network.bob.org.
1		IN	PTR	gateway.bob.org.
2		IN	PTR	dns.bob.org.
3		IN	PTR	dns2.bob.org.
4		IN	PTR	bob.org.
5		IN	PTR	bob5.bob.org.
6		IN	PTR	bob6.bob.org.

[Skipped a few lines]

253		IN	PTR	bob253.bob.org.
254		IN	PTR	bob254.bob.org.
255		IN	PTR	broadcast.bob.org.

Whenever you change any of these two files you will need to also update the serial number. Usually the serial number is just another form of the date so that you always create later numbers. In this example the serial number is the date in the form YYYYMMDD## where ## stands for the version number for the day. It is quite possible to change the serial number for the DNS more than 10 times a day so it is best to have 2 digits to use. Also, whenever you make a change you will need to restart the DNS in order to have the changes take affect.

bash# /etc/rc.d/init.d/named restart