An SRV record is published at a name of the form _service._protocol.domain, for example _sip._tcp.example.com. Its value has four parts: priority, weight, port and target hostname. Clients contact the lowest priority first; among records with the same priority, the weight decides what share of the traffic each one receives.
Because the record includes the port, a service can run on a non-standard port without users having to know it. SRV is used by protocols such as SIP, XMPP, LDAP and by some collaboration and game services. Web browsers do not use SRV records for HTTP, which is why a website cannot be moved to another port this way.
As with MX records, the target must be a hostname with its own address records, not a CNAME.
Example
_sip._tcp.example.com. 3600 IN SRV 10 60 5060 sip1.example.com.
; priority weight port target