Building a secondary (slave) DNS server
To guarantee high-availability in your network, it can be useful to operate more than one DNS server in your environment to catch up with any server failures. This is particularly true if you run a public DNS server where continuous access to the service is crucial and where it is not uncommon to have five and more DNS servers at once. Since configuring and managing multiple DNS servers can be time consuming, the BIND DNS server uses the feature of transferring zone files between the nodes so that every DNS server has the same domain resolving and configuration information. In order to do this, we need to define one primary and one or more secondary or slave DNS servers. Then we only have to adjust our zone file once on the primary server which will transfer the current version to all our secondary servers, keeping everything consistent and up-to-date. For a client it will then make no difference which DNS server they are connecting to.
