Format of an SRV record
The record name has three parts — _service._proto.name, for example _sip._tcp.example.com. The value holds four fields:
- Priority — clients try records with the lower value first.
- Weight — spreads load across hosts that share the same priority.
- Port — the service port, for example 5060 for SIP.
- Target — the host name, which must have a regular A record.
Where it is used
SRV removes hard-coded ports: the client learns from DNS where to connect. For instance, _sip._tcp.example.com with the value 10 0 5060 sip.example.com sends a SIP client to port 5060 on sip.example.com. SIP telephony, XMPP, LDAP, Minecraft servers and other protocols rely on SRV, while how often clients re-query is governed by the TTL.
