If you're running Linux and don't want your ISP to automatically change the contents of your resolv.conf file every time you receive a new IP address via DHCP, then do the following.
Assuming that you're using eth0 for your external connection, add the directive "PEERDNS=no" to your /etc/sysconfig/network-scripts/ifcfg-eth0 file.
How to stop DHCP from changing Linux resolv.conf file.
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