Split DNS allows you to use separate DNS servers for internal and external requests.
Enable Split DNS: Select this to enable Split DNS.
Primary Split DNS: This is the IP address of the first DNS server to be used in URL name lookups.
Secondary Split DNS: This DNS server is used in addition to the primary DNS server and acts as a backup DNS server if the primary split DNS server is unreachable. When choosing a secondary DNS server be sure to choose a server on a separate network from the primary DNS server. Choosing DNS servers that are on separate networks helps ensure that a network outage at a single data center won't completely disable your DNS lookups.