Glossary · DNS

SRV Record (Service Record)

An SRV record tells clients the host, port, priority and weight for a specific service, such as SIP, XMPP or Microsoft 365 autodiscover.

Updated October 5, 2026

An SRV (service) record specifies the hostname and port where a particular service runs, along with priority and weight values for choosing among several servers. The record name encodes the service and protocol.

Why it matters

Without SRV, clients must assume a fixed port. With it, you can move a service to another host or port, or spread load across servers, without changing client configuration. Voice, chat, directory and some game and collaboration protocols depend on it. Ordinary web browsers do not use SRV to find websites; for HTTP they use A and AAAA records.

Example

_sip._tcp.example.com.  3600 IN SRV 10 60 5060 sip1.example.com.
_sip._tcp.example.com.  3600 IN SRV 10 40 5060 sip2.example.com.
_sip._tcp.example.com.  3600 IN SRV 20  0 5060 backup.example.com.

Fields are priority, weight, port, target. Lowest priority is tried first; among equal priorities, weight sets the share (here about 60/40). Query with dig SRV _sip._tcp.example.com.

Common mistakes

  • Getting the name format wrong. It is _service._proto.name, with leading underscores.
  • Pointing the target at an IP address or a CNAME. It must be a hostname with address records.
  • Expecting a firewall or port to be open because the record exists. Verify with a port check.
  • Setting all weights to 0 and assuming even distribution; check the client's behavior.

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