A slave DNS domain is one for which your system acts as a backup for the master server. They are used to spread the load of serving DNS, and to allow clients to still resolve names in the domain if the master is temporarily down or un-reachable. Records are transferred from the master to slaves periodically, or when they change.

Typically, when a virtual server is created using Virtualmin a master DNS domain is created on the same system. Slaves can also be setup on other systems, as explained on the DNS Slave Auto-Configuration Quickstart page.

However, in some cases the master domain may be hosted on a different system, such as one run by the client who owns the domain. In this case, the Slave DNS plugin can be used to easily create and manage a local backup for the domain, to increase reliability or to satisfy registrar requirements on the number of nameservers a zone needs.

The simplest way to install the plugin on a system that is configured to use the Virtualmin YUM or APT repository is as follows :

1. Login to Virtualmin as root, and click on optional Virtualmin packages on the right-hand System Information page.
2. Check the box next to the wbm-virtuamin-slavedns or webmin-virtualmin-slavedns package, and click the Update Selected Packages button.
3. If all goes well, it will be downloaded from the repository and installed on your system.
4. Open the System Settings category on the left menu, and click on Features and Plugins.
5. Check the box next to Slave DNS domain, and click Save.

Unless some error message about plugin or feature dependencies appears, it is now almost ready for use.

Before a slave DNS domain can be created, a default master DNS server address must be configured. This can be later changed on a per-domain basis. To set the default, the steps to follow are :

1. Open the System Settings category on Virtualmin's left menu, and click on Server Templates.
2. Click on the Default Settings template, then select the Plugin options category.
3. In the Default slave zone masters field, enter one or more master DNS server IPs.
4. If your BIND DNS server uses views, the one to create slave zones in should be selected from the Add slave zones to view menu.
5. Click Save.

Once the plugin is fully configured, creating a slave domain is as simple as selecting the Setup slave DNS zone? box on the Create Virtual Server form. Or you can enable it for an existing server on the Edit Virtual Server page. Either way, the slave domain will be added to the BIND configuration, and setup to replicate records from the default masters.

Naturally, it is impossible to enable both the master and slave DNS domain features for the same virtual server.

Once a virtual server has the slave DNS feature enabled, you can change the IP address of the master DNS server as follows :

1. Select the domain from Virtualmin's left menu.
2. Under the Services menu, click on Configure Slave DNS Zone.
3. Change the IPs in the Master server IP addresses field, then click Save.

If records have been successfully transferred from the master, they will be listed on this page.