Creating the resolv.conf File

A simple example resolv.conf file for a client (non-server) machine in the doc.com domain is shown in Example 12-1:

Example 12-1 Sample resolv.conf File

; Sample resolv.conf file for the machine polaris
domain doc.com
; try local name server
nameserver 127.0.0.1
; if local name server down, try these servers
nameserver 123.45.6.1
nameserver 111.22.3.5
; sort the addresses returned by gethostbyname(3c)
sortlist
130.155.160.0/255.255.240.0
130.155.0.0

The first line of the /etc/resolv.conf file lists the domain name in the form:

domain domainname

Where domainname is the name registered with the Internet governing bodies (as of this writing, the InterNIC).

No spaces or tabs are permitted at the end of the domain name. Make sure that you enter a hard carriage return immediately after the last character of the domain name.

The second line identifies the loopback name server in the form:

nameserver 127.0.0.1

Succeeding lines list the IP addresses of up to three DNS master, secondary, or cache-only name servers that the resolver should consult to resolve queries. (Do not list more than three primary or secondary servers.) Name server entries have the form:

nameserver IP_address

Where IP_address is the IP address of a primary or secondary DNS name server. The resolver queries these name servers in the order they are listed until it obtains the information it needs.

The fifth line of the /etc/resolv.conf file lists the address sortlist in the form:

sortlist
addresslist

Where addresslist specifies the sort order of the addresses returned by gethostbyname(3c). In our example, gethostbyname returns the netmask pair 130.155.160.0/255.255.240.0 ahead of the IP address 130.155.0.0.