Server Domain Name Resolution - Yealink CP969 Administrator's Manual

Click Confirm to accept the change.
7.

Server Domain Name Resolution

If a domain name is configured for a server, the IP address(es) associated with that domain
name will be resolved through DNS as specified by
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, A query will be performed only. If a 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.
NAPTR (Naming Authority Pointer)
First, the IP phone sends NAPTR query to get the NAPTR pointer and transport protocol.
Example of NAPTR records:
order
IN NAPTR 90
IN NAPTR 100
Parameters are explained in the following table:
Parameter
order
pref
Flags
service
regexp
replacement
The IP phone picks the first record because its order of 90 is lower than 100. The pref parameter
pref flags service
50 "s" "SIP+D2T"
50 "s" "SIP+D2U"
Specify preferential treatment for the specific record. The order is from
lowest to highest, lower order is more preferred.
Specify the preference for processing multiple NAPTR records with the
same order value. Lower value is more preferred.
The flag "s" means to perform an SRV lookup.
Specify the transport protocols:
SIP+D2U: SIP over UDP
SIP+D2T: SIP over TCP
SIP+D2S: SIP over SCTP
SIPS+D2T: SIPS over TCP
Always empty for SIP services.
Specify a domain name for the next query.
Configuring Advanced Features
RFC 3263. The DNS query involves NAPTR,
regexp replacement
"" _sip._tcp.yealink.pbx.com
"" _sip._udp.yealink.pbx.com
Description
581