Configuring Advanced Features399Parameters Permitted Values DefaultPhone User Interface:NoneFailover redundancy can only be utilized when the configured domain name of the SIPserver is resolved to multiple IP addresses. If the IP phone is not configured with a DNSserver, or the DNS query returns no result from a DNS server, you can configure a set ofDNS NAPTR/SRV/A records into the IP phone. The IP phone will attempt to resolve thedomain name of the SIP server with static DNS cache.When the IP phone is configured with a DNS server, the IP phone will behave as followsto resolve domain name of the SIP server: The IP phone performs a DNS query to resolve the domain name from the DNSserver. If the DNS query returns no results for the domain name, or the returned recordcannot be contacted, the values in the static DNS cache (if configured) are usedwhen their configured time intervals are not elapsed. If the configured time interval is elapsed, the IP phone will attempt to perform aDNS query again. If the DNS query returns a result, the IP phone will use the returned record andignore the statically 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.
