Mitel 6800 Series Administrator's Manual page 637

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.
Note: The "sip dns srvX weight" parameter must be configured but the phones will
support this feature in a future release.
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 balance across the three target host names.
Bigbox will get 60% of the load, and smallbox1 and smallbox2 will each get 20% load.
If all three servers with priority 10 are unavailable, the next highest priority record is selected,
in this case backupbox. This could be a server in another physical location.
The server entries in the startup.cfg file can use DNS hostnames or can use IP addresses. If
hostnames are used, any pre-cached DNS A records via the host file mechanism are used
before resorting to live DNS query if there is no local match.
For example, the following hostfile.text uses IP addresses that are used in the DNS server
queries:
hostfile.txt
Advanced Operational Features
6-48