DNS settings

DNS setting define the DNS servers to contact to resolve host names to IP addresses.

The primary behavior to configure for host name resolution consists of the following definitions:
  • Which domains to search for a match when a host name without a domain qualifier is submitted. The appliance attempts to resolve a host name with any domain in the domain name table. The host name is resolved to the first found match.
  • Which DNS servers to contact and their contact order.
  • The load-balancing algorithm to contact name servers:
    • First alive. This algorithm maintains a list of servers and forwards a new connection to the next server on the list.
    • Round robin. This algorithm uses the concept of a primary server and one or more backup servers. When the primary server is available, all connections are forwarded to this server. When the primary server is unavailable, connections are forwarded to backup servers. The primary server is the first server in the list.

The results from DNS resolution requests are cached to improve performance. When a name server responds with an IP address, the response includes its time to live (TTL) in the cache. The appliance uses the value from the DNS response or 10 seconds, whichever is greater. If the name server responds that a host name has no associated IP address, the appliance caches the negative response for 30 seconds.