Installation guide

Advanced Operational Features
41-001561-00 REV00 – 10.2014 6-36
The SIP registration and SIP proxy features on the phones previously allowed the use of server queries only to live DNS
servers. Using the host file and specific DNS SVR parameters extends this mechanism to allow pre-configuration of server
values in the aastra.cfg file. The following new parameters are used for this feature:
• sip dns srvX name
• sip dns srvX priority
• sip dns srvX weight (supported in a future release)
• sip dns srvX port
• sip dns srvX target
You can configure up to 4 DNS SRV records, with each server having a priority which tells the phone which server to use,
and a host name or target. The IP phone will use the DNS SRV record with the lowest-numbered priority value first, and
will only failover to other records if the connection with this record's host fails. Thus a service may have a designated
failover server, which is only used if the primary server fails.
If a service has multiple SRV records with the same priority value, the IP phone(s) use the weight field to determine which
host to use. The weight value is a ratio compared to the weight of other records with the same name and priority value.
In the following example, both the priority and weight fields are used to provide a combination of load balancing and
backup service.
Example
sip dns srv1 name: _sip._udp.example.com
sip dns srv1 priority: 10
sip dns srv1 weight: 60
sip dns srv1 port: 5060
sip dns srv1 target: bigbox.example.com
sip dns srv2 name: _sip._udp.example.com
sip dns srv2 priority: 10
sip dns srv2 weight: 20
sip dns srv2 port: 5060
sip dns srv2 target: smallbox1.example.com
sip dns srv3 name: _sip._udp.example.com
sip dns srv3 priority: 10
sip dns srv3 weight: 20
sip dns srv3 port: 5060
sip dns srv3 target: smallbox2.example.com
sip dns srv4 name: _sip._udp.example.com
sip dns srv4 priority: 20
sip dns srv4 weight: 10
sip dns srv4 port: 5060
sip dns srv4 target: backupbox.example.com
The first three records (SRV 1, 2, and 3) share a priority of 10, so the weight field's value is used by the phones to load bal-
ance across the three target host names.
Bigbox will get 60% of the load, and smallbox1 and smallbox2 will each get 20% load.
Note:
The “X” indicates a DNS SRV with a value from 1 to 4.
Note:
The “sip dns srvX weight” parameter must be configured but the phones will support this feature in a future release.