Administrator’s Guide for SIP-T2 Series/T19(P) E2/T4 Series/CP860 IP Phones666Static DNS CacheFailover redundancy can only be utilized when the configured domain name of the server isresolved to multiple IP addresses. If the IP phone is not configured with a DNS server, or theDNS query returns no result from a DNS server, you can configure a set of DNS NAPTR/SRV/Arecords into the IP phone. The IP phone will attempt to resolve the domain name of the SIPserver with static DNS cache.When the IP phone is configured with a DNS server, the IP phone will behave as follows toresolve domain name of the server: The IP phone performs a DNS query to resolve the domain name from the DNS server. If the DNS query returns no results for the domain name, or the returned record cannot becontacted, the values in the static DNS cache (if configured) are used when theirconfigured time intervals are not elapsed. If the configured time interval is elapsed, the IP phone will attempt to perform a DNS queryagain. If the DNS query returns a result, the IP phone will use the returned record and ignore thestatically configured cache values.When the IP phone is not configured with a DNS server, it will behave as follow: The IP phone attempts to resolve the domain name within the static DNS cache. The IP phone will always use the results returned from the static DNS cache.IP phones can be configured to use static DNS cache preferentially. Static DNS cache isconfigurable on a per-line basis.
