Configuring Advanced Features5817. Click Confirm to accept the change.Server Domain Name ResolutionIf a domain name is configured for a server, the IP address(es) associated with that domainname will be resolved through DNS as specified by RFC 3263. The DNS query involves NAPTR,SRV and A queries, which allows the IP phone to adapt to various deployment environments.The IP phone performs NAPTR query for the NAPTR pointer and transport protocol (UDP, TCPand TLS), the SRV query on the record returned from the NAPTR for the target domain nameand the port number, and the A query for the IP addresses.If an explicit port (except 0) is specified, A query will be performed only. If a server port is set to0 and the transport type is set to DNS-NAPTR, NAPTR and SRV queries will be tried beforefalling to A query. If no port is found through the DNS query, 5060 will be used.The following details the procedures of DNS query for the IP phone to resolve the domain name(e.g., yealink.pbx.com) of working server into the IP address, port and transport protocol.NAPTR (Naming Authority Pointer)First, the IP phone sends NAPTR query to get the NAPTR pointer and transport protocol.Example of NAPTR records:order pref flags service regexp replacementIN NAPTR 90 50 "s" "SIP+D2T" "" _sip._tcp.yealink.pbx.comIN NAPTR 100 50 "s" "SIP+D2U" "" _sip._udp.yealink.pbx.comParameters are explained in the following table:Parameter Descriptionorder Specify preferential treatment for the specific record. The order is fromlowest to highest, lower order is more preferred.pref Specify the preference for processing multiple NAPTR records with thesame order value. Lower value is more preferred.Flags The flag “s” means to perform an SRV lookup.serviceSpecify the transport protocols:SIP+D2U: SIP over UDPSIP+D2T: SIP over TCPSIP+D2S: SIP over SCTPSIPS+D2T: SIPS over TCPregexp Always empty for SIP services.replacement Specify a domain name for the next query.The IP phone picks the first record because its order of 90 is lower than 100. The pref parameter
