SRV records provide a standard way of allowing services to use different values, and for a program to determine what those connection values are.
Related Wikipedia page:
http://en.wikipedia.org/wiki/SRV_record
As per the Wikipedia page, the format will look like this:
_service._proto.name TTL class SRV priority weight port target
We’ll use their example:
_sip._tcp.example.com. 86400 IN SRV 0 5 5060 sipserver.example.com.
The red portion goes onto the left side of the SRV record in DA, and the blue portion goes onto the right side (DA sets the TTL automatically for you)
The Red portion of the contains the service, protocol, and name, in that order, separated by the period ‘.’ character.
In the above example, the values match up as follows:
service: _sip
protocol: _tcp
name: example.com.
priority: 0
weight: 5
port: 5060
target: sipserver.example.com.
Note that the “name” value will always match the name of the zone.
As such, these 2 left-side values are equivalent, and either could be used:
_sip._tcp.example.com.
_sip._tcp
where any left-side value that does not end with a period ‘.’ will have the zone name appended to the end.
The “target” value can be any domain value, but should resolve using an A or CNAME record.
The same rule about the value ending in a period applies, and would be mandatory if the target is on a different domain name.