About DNS Caching
You configure a local domain name servers (DNS) for caching under Optimization > Branch Services: Caching DNS. By default, the DNS cache is disabled.
A DNS name server resolves hostnames to IP addresses and stores them locally in a single appliance. Any time your browser requests a URL, it first looks in the local cache to see if it is there before querying the external name server. If it finds the resolved URL locally, it uses that IP address.
This feature is a nontransparent DNS caching service. Any client machine must point to the client-side appliance as its DNS server.
Hosting the DNS name server function provides:
• improved performance for applications by saving the round trips previously needed to resolve names. Whenever the name server receives address information for another host or domain, it stores that information for a specified period of time. That way, if it receives another name resolution request for that host or domain, the name server has the address information ready, and does not need to send another request across the WAN.
• improved performance for services by saving round trips previously required for updates.
• continuous DNS service locally when the WAN is disconnected, with no local administration needed, eliminating the need for DNS servers at branch offices.
A cache holds the resolved address entries information.