In this section of the Server set properties dialog, you can specify which DNS servers to update for this server set (whenever a server fails or comes back online).
Update the default DNS servers (configuration in Options dialog)
Enable this to update the default DNS servers configured in the Options dialog / DNS updating section for this server set.Update the following DNS servers (for this server set only)
List of DNS servers to update for this server set.
Use the Add button to add a new DNS server - see DNS server properties dialog.
Use the Edit button to update the selected DNS server - see DNS server properties dialog.
Use the Remove button to remove the selected DNS server.