To setup a secondary dns you just need to install bind and create a /etc/named.conf where you define the zones like this:
Code:
zone "domain.comr" {
type slave;
file "domain.com";
masters {xx.xx.xx.xx;};
};
where xx.xx.xx.xx is the IP of your primary dns. Of course you must allow-transfer from the primary to the secondary for automatic zones updating.