Yealink SIP-T48G [178/465] Sip server domain name resolution

Administrator’s Guide for SIP-T4X IP Phones

164

Procedure

Server redundancy can be configured using the configuration files or locally.

Configuration File

<MAC>.cfg

Configure the server

redundancy on the IP phone.

For more information, refer to

Server Redundancy on page

338.

Local

Web User Interface

Configure the server

redundancy on the IP phone.

Navigate to:

http://<phoneIPAddress>/servl

et?p=account-register&q=load

&acc=0

If a domain name is configured for a SIP server, the IP address(es) associated with that

domain name will be discovered 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 the NAPTR query for the SRV pointer

and service type (UDP, TCP and TLS), the SRV query on the record returned from the

NAPTR for the host name and the port number, and the A query for the IP addresses.

If a port is set to 0 and the transport type is set to DNS-NAPTR, NAPTR and SRV queries

will be tried before falling back to A query. If no port is found through the DNS query,

5060 will be used. If an explicit port (except 0) is specified and the transport type is set

to DNS-NAPTR, the only lookup will be an A query.

The following details the procedures of DNS query for the IP phone to resolve the

domain name of working server into the IP address, port and transport protocol.

NAPTR (Naming Authority Pointer)

First, the IP phone sends the NAPTR query to get the SRV pointer and service type. The IP

phone performs a NAPTR query for the domain name. Example of NAPTR records:

order pref flags service regexp replacement

IN NAPTR 90 50 "s" "SIP+D2T" "" _sip._tcp.example.com

IN NAPTR 100 50 "s" "SIP+D2U" "" _sip._udp.example.com