SIP 604 Does Not Exist Anywhere: what it means and how to fix it

Short answer: SIP 604 Does Not Exist Anywhere means the server has authoritative information that the user or number in the Request-URI does not exist anywhere. It is the global version of 404 Not Found. The most common causes are a disconnected number, a typo or an invalid format. Check the number sent in the INVITE before you open a ticket.

How Monitor treats SIP 604

The reading depends on what should answer the number, which is the question 2N5 answers when it adds each circuit. These are the rules the product applies today, generated from the same function that judges every test call.

What should answer the number	Reading
A greeting or recorded message (the IVR)	Down
A test tone or echo service	Down
Other: it may ring or be answered	Down

What Monitor records for an IVR: The call was refused, and the provider said it would fail everywhere (SIP 604).

A call read as Down alerts nobody on its own: it is repeated 3 times, every 2 minutes, and only 4 failures in a row open an incident, with each call's SIP code and Q.850 cause as evidence for the carrier. At the default pace, every circuit is tested every 15 minutes.

If the carrier returns SIP 604 when 2N5's calling account registers, before any call, the test is monitoring blind: it is a problem on 2N5's side, it does not count against the circuit and it does not alert the customer.

What does SIP 604 mean in practice?

SIP 604 Does Not Exist Anywhere is a 6xx global failure. Under RFC 3261, the server has authoritative information that the user named in the Request-URI does not exist anywhere. That is a stronger statement than SIP 404, which only says the user was not found in that domain. A proxy that receives a 604 cancels its pending attempts and does not look for other routes.

Where SIP meets the phone network, RFC 3398 converts a 604 into Q.850 cause 1 (Unallocated number). The SIP 604 error is rare: most carriers signal a nonexistent number with a 404. When it does show up, check the number that went out in the INVITE first, because a wrong format produces the same result as a disconnected number.

Common causes in Brazil

• A number that was disconnected or never assigned by the carrier.
• The wrong format in the INVITE: a missing area code (DDD), a missing ninth digit on a mobile number or an incomplete 0800 (toll-free) number, or a country code when the trunk expects the national format.
• Digit manipulation on the PBX’s outbound route (Asterisk, Issabel, FreePBX, 3CX) cutting digits or adding extra ones.
• An extension or user that does not exist on a destination PBX configured to respond 604 instead of 404.
• A recently ported number whose routing has not been updated yet on the route used.

How to troubleshoot

1. Open the call in sngrep and read the Request-URI and the To header of the INVITE. Check the number digit by digit.
2. In Asterisk, Issabel or FreePBX, turn on pjsip set logger on (or sip set debug on in chan_sip) and compare the number dialed by the extension with the one sent to the trunk.
3. Review the digit manipulation rules on the outbound route, such as prefixes being added or removed.
4. Call the same number from a mobile phone. If it completes, the problem is the format or the route, not the number.
5. In 3CX, turn on verbose logging and check the Activity Log for the number sent to the trunk.
6. Look for Reason: Q.850;cause=1 in the response, which confirms an unallocated number.

What to send your carrier

• The exact date and time with the time zone, for example 2026-10-07 14:32:10 -03:00.
• The calling number (A) and the called number (B), exactly as they went out in the Request-URI.
• The Call-ID and the full SIP/2.0 604 Does Not Exist Anywhere line, with the Reason header, if present.
• Whether the number completes from a mobile phone or another trunk.
• The pcap file of the capture, if you have one.

Frequently asked questions

What is the difference between SIP 604 and SIP 404?

404 Not Found says the user was not found in that domain or on that server. 604 Does Not Exist Anywhere goes further: the server has authoritative information that the user does not exist anywhere, so no other route should be tried. In practice, the 404 is far more common on Brazilian trunks.

Which Q.850 cause goes with a SIP 604?

Under RFC 3398, a gateway converts a SIP 604 into Q.850 cause 1 (Unallocated number). In the other direction, cause 1 becomes a 404, not a 604. So a 604 that reaches your PBX was almost always generated by SIP equipment, not translated from a telephone exchange.

Does a real test call catch this error?

Yes. A real test call receives the final SIP response the network returns, including a 604. When the result counts as a failure, the call is retried before any alert goes out, and the alert is sent by email and SMS.