Yealink SIP-T2xP Administrator's Manual page 199

5. Configure parameters of the SIP server 1 or SIP server 2 in the corresponding fields.
You must set the port of SIP server to 0 for NAPTR, SRV and A queries.
6. Click Confirm to accept the change.
If the outbound proxy server is required and the transport is set to DNS-NAPTR, you must
Note
set the port of outbound proxy server to 0 for NAPTR, SRV and A queries.
If a domain name is configured for a SIP server, the IP address(es) associated with that
domain name 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 , TCP and TLS), the SRV query on the record returned from
the NAPTR for the target domain name and the port number, and the A query for the IP
addresses.
If an explicit port (except 0) is specified and the transport type is set to DNS-NAPTR, A
query will be performed only. If a SIP server port is set to 0 and the transport type is set
to DNS-NAPTR, NAPTR and SRV queries will be tried before falling 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.
Configuring Advanced Features
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