Avaya 1230 - SIP Domain DNS Lookup Feature

SIP Domain DNS Lookup feature
The DNS Lookup feature enables the IP Deskphone to discover IP addresses for a specified SIP
domain using DNS.
There are two ways the DNS Lookup feature can provide SIP domain IP addresses to the IP
Deskphone:
1. using DNS SRV records (refer to RFC2782)
2. using DNS A/AAAA records (IPv4/IPv6 address records)
How DNS lookup works
One or two IP addresses can be configured for a particular SIP domain - primary and secondary IP
addresses:
• SERVER_IP[x]_1
• SERVER_IP[x]_2
where x = the domain number from 1 to 5.
If the IP Deskphone attempts to log on using these configured addresses and fails to do so, the IP
Deskphone then tries to discover the IP addresses using DNS. If there is no primary or secondary
SIP domain IP address configured, then the IP Deskphone uses DNS to determine the IP address. If
only SERVER_IP[x]_2 is configured (SERVER_IP[x]_1 is 0.0.0.0), then DNS Lookup is used first; if
DNS Lookup fails, only then is the secondary IP address tried.
The DNS Lookup feature tries to obtain SIP domain IP addresses through DNS SRV records, using
the domain name as a parameter for UDP, TCP, and TLS. Multiple SRV records can be configured
for each domain and for each transport protocol (UDP, TCP and TLS). The hostname is returned
instead of the IP address. The hostname must point to an address record (A or AAAA record).
SRV record example:
_sip._tcp.example.com. 86400 IN SRV 0 5 5060 sipserver.example.com
where:
• sip = the desired service
• tcp = the transport protocol
• example.com = the configured domain name
• 5060 = the port to be used
• sipserver.example.com = the SIP proxy to be used (hostname is replaced by the IP address
using A/AAAA records)
The DNS Lookup feature then tries to find the IP address of the SIP domain in A/AAAA records on
the DNS Server. Only the IP address is returned; therefore, default ports are used — 5060 for
UDP/TCP and 5061 for TLS.
Features
206 SIP Software for Avaya 1200 Series IP Deskphones-Administration March 2015
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