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dns guide

SIP DNS SRV Records

SIP domains often use DNS SRV records so phones, trunks, and soft clients can discover the correct SIP host, transport, and port without hardcoding a single server.

Record Names

  • _sip._udp.example.com is used for SIP over UDP.
  • _sip._tcp.example.com is used for SIP over TCP.
  • _sips._tcp.example.com is used for SIP over TLS.

Priority And Weight

Lower priority values are preferred first. Weight controls balancing between records with the same priority. The SRV target then needs A or AAAA records.

Troubleshooting Clues

  • Missing SRV records can prevent registration by domain.
  • Wrong ports can send clients to the wrong listener.
  • SRV targets without A or AAAA records will fail after discovery.
  • Long TTLs can delay routing changes.