If you have named server on rhel and want to install and config slave bind server for backup your dns server, here this a simple step:

install bind (if not install yet), for RHEL it is easy to install bind you have to install this package using "rpm -Uvh" from dvd or using yum
- bind (includes DNS server, named)
- bind-utils (utilities for querying DNS servers about host information)
- bind-libs (libraries used by the bind server and utils package)
- bind-chroot (tree of files which can be used as a chroot jail for bind)
- caching-nameserver (config files for a simple caching nameserver)

edit named.conf and named.rfc1912.zones or copy from your master bind server to /var/named/chroot/etc/named.conf and /var/named/chroot/etc/named.rfc1912.zones

change your zone config to be a slave server for your zone:

zone "example.com" IN {
type slave;
file "slaves/yourzonefile";
masters { your master ip; };
allow-update { your master ip; };

change your named.conf in master server:

zone "example.com" IN {
type master;
file "yourzonefile";
also-notify { your slave server ip1; your slave server ip2; }

restart you bind server, when you edit zonefile you have to edit serial to notify slave server to known that zone data is outdate and refresh it with master server.