SIP response codes
SIP 401 Unauthorized
The registrar or server asks for credentials. A normal step: the phone repeats the request with an Authorization header.
- Name
- Unauthorized
- Class
- 4xx · Client error
- Defined in
- RFC 3261
When it happens
- Every REGISTER without credentials gets a 401 first.
What to check
- A 401 repeated after the phone sent credentials means the username, password or realm is wrong.
- Check that the server clock and nonce handling are fine if it fails only now and then.
What the response looks like
SIP/2.0 401 Unauthorized
Via: SIP/2.0/UDP 203.0.113.10:5060;branch=z9hG4bK776asdhds
From: <sip:101@pbx.example>;tag=1928301774
To: <sip:+15551234567@pbx.example>;tag=a6c85cf
Call-ID: a84b4c76e66710@203.0.113.10
CSeq: 2 INVITE
Reason: Q.850;cause=21;text="Call rejected"
Content-Length: 0