SIP 404 Not Found
The user does not exist in the domain in the Request-URI.
4xx Client failure · RFC 3261 · Answer to OPTIONS: Up. It doesn't know the address we asked for.
What SIP 404 means
A 404 says the server has definite information that the user in the Request-URI doesn't exist in that domain. On a trunk the user is a phone number, so 404 usually means the number isn't in the dial plan, isn't assigned, or is written in a format the server doesn't match.
Gateways map the phone network's Q.850 cause 1, unallocated number, to 404 under RFC 3398, so a 404 on an outbound call can come from the far end of the PSTN rather than from your carrier. On REGISTER it means the account doesn't exist, and on OPTIONS it means the server doesn't recognise the address you asked for.
Example response
SIP/2.0 404 Not Found
Via: SIP/2.0/UDP 198.51.100.18:5060;branch=z9hG4bK-404-k1
From: <sip:+[email protected]>;tag=f19a
To: <sip:[email protected]>;tag=nf-42
Call-ID: [email protected]
CSeq: 2 INVITE
Reason: Q.850;cause=1;text="Unallocated (unassigned) number"
Content-Length: 0Common causes of SIP 404
- The number isn't in the PBX or SBC dial plan, so there is nowhere to route it.
- The number is sent in national format while the carrier expects E.164, or the other way round.
- The number was ported or cancelled, and the carrier no longer routes it to you.
- The Request-URI names a domain or host the server doesn't serve.
- The phone network reported the number as unallocated, and the gateway mapped Q.850 cause 1 to 404.
How to fix SIP 404
- Compare the Request-URI's user part, character by character, with the number format the carrier documents.
- Check the dial plan or inbound routing on the system that sent the 404.
- Read the Reason header: Q.850 cause 1 means the phone network doesn't know the number, not that your trunk is broken.
- For a number you own, confirm with the carrier that it is still assigned and pointed at your trunk.
- Dial the number from another network to tell a routing problem from a number that really doesn't exist.
SIP 404 as an answer to OPTIONS
A 404 to OPTIONS means the server is up but doesn't know the address in the Request-URI. Many SBCs answer OPTIONS for an unknown user or domain this way, so it often just means the probe asked for a name the SBC doesn't serve. A PingVo Route counts it as reachable by default; set the expected codes to 200 if it should count as a failure.
Questions about SIP 404
Is SIP 404 always the number's fault?
No. It says the server couldn't match the address. That can be a dial plan gap or a format mismatch just as much as a number that doesn't exist.
What is the difference between SIP 404 and 604?
404 means the user doesn't exist at this server. 604 Does Not Exist Anywhere is a global answer: the user isn't found anywhere, so trying other servers is pointless.
Why do inbound calls to my number get 404?
The call reached a system that has no route for the number, often after a port or a dial plan change. Check where the carrier delivers the number and whether that system knows it.