SIP 404 Not Found

What SIP 404 means

The number or extension you dialled does not exist on the system that answered. On a business phone system this is usually a dial plan stripping or adding digits, a DDI that was never provisioned on the trunk, or an extension that has been deleted.

Client error (4xx)
Sent by The destination server or your own PBX
Common

What SIP 404 Not Found actually means

The server has definitive information that the user in the request URI does not exist at the domain given. It is a statement about that domain only, which is what separates it from a 604: a 404 says "not here", a 604 says "nowhere at all".

What causes SIP 404 on a business phone system

The dial plan is changing the number before it leavesDigit manipulation rules that strip a leading zero or add a trunk prefix will happily produce a number nobody owns. This is the most common cause on a newly configured system, and it shows up as every external call failing while internal calls work.
The DDI is not provisioned on the trunkFor inbound calls, a number your provider has not pointed at your trunk cannot be delivered even though you own it. Common immediately after adding numbers or completing a port.
The extension has been deleted or renumberedSpeed dials, BLF keys and old divert rules keep pointing at extensions that no longer exist, so the failure appears long after the change that caused it.
The number has been ported away or ceasedA number that has moved to another provider stops existing on the old platform. Where an internal directory still lists it, staff keep dialling it and keep getting a 404.

How to fix SIP 404

Establish whether it is inbound or outbound that failsThey have entirely different causes. Outbound points at your dial plan; inbound points at how your provider has routed the DDI. Test both before changing anything.
Read the number as it actually leaves the systemTake a SIP trace or read the PBX log and look at the request URI. Comparing what was dialled against what was sent exposes digit manipulation immediately.
Confirm the DDI is routed to your trunkIn your provider portal, check the number is present and pointed at the right trunk or endpoint. Numbers added to an account are not always routed automatically.
Check the extension exists and clear stale referencesFor internal failures, confirm the extension is still configured, then clean up the BLF keys, speed dials and divert rules that still reference the old number.

Fixing the underlying problem

This page explains the code. These guides walk through the fix in detail.

Questions about SIP 404

What does SIP 404 Not Found mean?

The system that answered has no record of the number or extension you dialled. It is the SIP equivalent of an unobtainable tone: the call reached a server, and that server knows the destination does not exist in its domain.

What is the difference between SIP 404 and SIP 604?

Scope. A 404 means the number does not exist on the system that answered, so it can still exist somewhere else and the fault may be in your routing. A 604 means no system anywhere recognises it, which usually means the number itself is wrong or unallocated.

Why do all my outbound calls fail with 404 on a new phone system?

Look at the dial plan first. A rule that strips a leading zero or adds a trunk prefix will send a number that does not exist, and it affects every external call while leaving internal calls working perfectly. Take a trace and compare the number dialled with the number actually sent.

Call hangup causes that become SIP 404

If the call crossed a gateway between SIP and ISDN or SS7, this status may have started life as one of these Q.850 cause values. The mapping is defined in RFC 3398 section 7.2.4.1.

Related SIP response codes

Source. SIP 404 Not Found is defined in RFC 3261 section 21.4.5 and registered in the IANA SIP Parameters — Response Codes. The causes and fixes above are drawn from our own experience supporting UK business phone systems.

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