linux-dns

gistfile1.txt

For a lot of distros the /etc/resolv.conf is autogenerated by NetworkManager or dhcp-client, in those cases usually 
/etc/resolv.conf contains a warning like:

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN

From Ubuntu Server Guide
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Traditionally, the file /etc/resolv.conf was a static configuration file that rarely needed to be
changed or automatically changed via DCHP client hooks. Nowadays, a computer can switch from
one network to another quite often and the resolvconf framework is now being used to track these
changes and update the resolver's configuration automatically. It acts as an intermediary between
programs that supply nameserver information and applications that need nameserver information.
Resolvconf gets populated with information by a set of hook scripts related to network interface
configuration. The most notable difference for the user is that any change manually done to /etc/
resolv.conf will be lost as it gets overwritten each time something triggers resolvconf. Instead,
resolvconf uses DHCP client hooks, and /etc/network/interfaces to generate a list of nameservers
and domains to put in /etc/resolv.conf, which is now a symlink:
/etc/resolv.conf -> ../run/resolvconf/resolv.conf

To configure the resolver, add the IP addresses of the nameservers that are appropriate for your
network in the file /etc/network/interfaces. You can also add an optional DNS suffix search-lists
to match your network domain names. For each other valid resolv.conf configuration option, you can
include, in the stanza, one line beginning with that option name with a dns- prefix. The resulting file
might look like the following:
iface eth0 inet static
 address 192.168.3.3
 netmask 255.255.255.0
 gateway 192.168.3.1
 dns-search example.com
 dns-nameservers 192.168.3.45 192.168.8.10
The search option can also be used with multiple domain names so that DNS queries will be
appended in the order in which they are entered. For example, your network may have multiple subdomains
to search; a parent domain of example.com, and two sub-domains, sales.example.com and
dev.example.com.
If you have multiple domains you wish to search, your configuration might look like the following:
iface eth0 inet static
 address 192.168.3.3
 netmask 255.255.255.0
 gateway 192.168.3.1
 dns-search example.com sales.example.com dev.example.com
 dns-nameservers 192.168.3.45 192.168.8.10
If you try to ping a host with the name of server1, your system will automatically query DNS for its
Fully Qualified Domain Name (FQDN) in the following order:
1. server1.example.com
2. server1.sales.example.com
3. server1.dev.example.com
If no matches are found, the DNS server will provide a result of notfound and the DNS query will fail.