Depending on just one server to provide a resource to your network is almost never a good idea. If our DNS server has a problem and fails, our network users will be unable to resolve any names, internal or external. To rectify this, we can actually set up a slave DNS server that will cache zone records from the master and allow name resolution to work in case the primary fails. This is not required, but redundancy is always a good thing.
To set up a secondary DNS server, we first need to configure our primary server to allow it to transfer zone records to a slave server. To do so, we'll need to edit the /etc/bind/named.conf.options file, which currently looks similar to the following:
options { directory ...
