Introduction

SIP and related voice services often rely on SRV records so clients can discover the right host and port automatically. When the SRV record is wrong, the service can look broken even though the server itself is fine. The fix is to verify the exact SRV name, protocol label, target hostname, and supporting A or AAAA records that the client expects.

Symptoms

  • SIP clients fail to auto-discover the service host or port
  • DNS lookups return no usable SRV answer for the expected service name
  • Some devices connect only when the server and port are entered manually
  • The issue started after moving providers or changing DNS zones
  • Public DNS shows a record, but clients still do not route calls correctly

Common Causes

  • The SRV record is published under the wrong service or protocol label
  • The target hostname in the SRV record does not resolve to a valid host record
  • Port, priority, or weight values are incorrect for the intended service
  • The DNS zone publishes the record correctly, but the client expects a different domain name
  • Multiple conflicting SRV records exist or the client does not actually support SRV discovery

Step-by-Step Fix

  1. Confirm the exact SRV name your SIP client or provider expects, including the service label, protocol label, and domain.
  2. Query the live SRV record from public DNS and verify the answer includes the correct target host and port.
  3. Check that the SRV target hostname resolves through A or AAAA records and points to the intended server.
  4. Review priority and weight values so they match your intended routing behavior rather than an old or default setup.
  5. Remove conflicting or malformed SRV records that could cause clients to choose the wrong destination.
  6. Compare the configured domain in the client or service with the domain where the SRV record is actually published.
  7. Test again from a client known to support SRV lookups so you can distinguish DNS issues from client limitations.
  8. Re-run public lookups and end-to-end SIP registration tests until discovery works without manual host entry.
  9. Document the exact SRV naming pattern for the service so future DNS edits do not break auto-discovery.