SIP Response Code

SIP 404 Not Found

6 min read · Updated April 2026

SIP 404 Not Found means the server has no record of the user or resource you requested. Unlike 480 (user known but unavailable) or 408 (network timeout), 404 means the destination simply does not exist on that server.

In this guide

01What SIP 404 Not Found means 02404 vs 480 vs 408 vs 503 03Common causes 04How to fix SIP 404 05Platform-specific fixes 06Diagnosing from a trace

1. What SIP 404 Not Found means

SIP 404 Not Found, defined in RFC 3261, means the server specifically knows the requested user does not exist on that server or domain. The Request-URI was well-formed and the server was reachable, but no matching user or resource was found.

404 is a definitive response — the user does not exist here. This is different from 480 (user exists but is unavailable) or 408 (server unreachable). A 404 tells you to look elsewhere or fix your routing.

2. SIP 404 vs 480 vs 408 vs 503

Code	Meaning	Cause
404	Not Found	User does not exist on this server
480	Temporarily Unavailable	User exists but is not registered or in DND
408	Request Timeout	Server was unreachable — no response
503	Service Unavailable	Server reachable but cannot handle request

3. Common causes of SIP 404

Cause 01

Wrong SIP server address

The INVITE or REGISTER is going to the wrong server. The Request-URI domain does not match any domain the server handles. Check DNS resolution — confirm the SIP server hostname resolves to the correct IP. Verify the outbound proxy and registrar addresses in your PBX configuration.

Cause 02

User does not exist on the server

The extension or user in the Request-URI has not been created on the PBX or registrar. Check that the user/extension exists in the PBX admin interface. For carrier trunks, verify the DID is provisioned on the account.

Cause 03

Domain mismatch in Request-URI

The PBX receives an INVITE for sip:1001@external.com but only knows about sip:1001@internal.com. The domains do not match so the server returns 404. Check is_myself() in Kamailio/OpenSIPS and the domain list in Asterisk. The server must recognize the domain in the Request-URI as its own.

Cause 04

Routing table miss

The call routing logic has no matching rule for the called number. In Asterisk dialplan: no matching exten for the dialed number. In Kamailio: lookup("location") returns false because there is no registered contact. Add the missing route or extension.

Cause 05

Number format mismatch

The called number arrives in E.164 format (+12025551234) but the PBX dialplan expects 10-digit (2025551234) or 4-digit extension format. Add a translation pattern or dialplan rule to normalize the number format before routing.

4. How to fix SIP 404

Wrong server: Check DNS — nslookup sip.provider.com. Verify the SIP server address in your trunk configuration matches exactly. Check for NAPTR/SRV records if the provider uses DNS-based routing.

User does not exist: Create the user/extension in PBX admin. For inbound DIDs, provision the number in your carrier portal and create a matching inbound route on the PBX.

Domain mismatch:

; Asterisk - add domain to local domain list
; In sip.conf (chan_sip):
domain=yourdomain.com

; Kamailio - add domain to domain table
opensipsctl domain add yourdomain.com

; Check is_myself() result in xlog
xlog("L_INFO", "[$ci] is_myself($rd): checking
");
if (!is_myself("$rd")) {
    xlog("L_WARN", "[$ci] Domain $rd not local - 404
");
    sl_send_reply("404", "Not Here");
    exit;
}

Number format: Add translation patterns in CUCM, or use Asterisk dialplan string manipulation:

; Asterisk - strip +1 prefix from E.164 for local routing
exten => _+1NXXXXXXXXX,1,Goto(internal,${EXTEN:2},1)
exten => _+NXXXXXXXXX,1,Goto(internal,${EXTEN:1},1)

5. Platform-specific 404 fixes

Asterisk

; Check if extension exists in dialplan
asterisk -r
dialplan show internal | grep 1001

; Check peer/endpoint exists
pjsip show endpoints
sip show peers

; Test routing for a number
dialplan show 12025551234@from-trunk

FreeSWITCH

; Check user directory
fs_cli
xml_locate directory domain example.com user 1001

; List all users
show users

6. Diagnosing SIP 404 from a trace

In a SIP trace, look at the Request-URI of the INVITE that received 404:

Is the domain in the Request-URI correct for the destination server?
Does the user part of the URI exist on that server?
Is the number format what the server expects?
Does the server return any Reason or Warning header with more detail?

Compare the Request-URI format against a working call on the same trunk to identify format differences.

Frequently asked questions

What does SIP 404 Not Found mean?

SIP 404 Not Found means the server has no record of the user or resource in the Request-URI. The server was reachable and understood the request, but the destination does not exist there. Unlike 480 (user exists but unavailable) or 408 (timeout), 404 is definitive — the user does not exist on that server or domain.

Why am I getting SIP 404 on inbound calls?

SIP 404 on inbound calls is usually caused by: the DID not provisioned on the carrier account, the PBX not having an inbound route matching the DID, number format mismatch (E.164 vs 10-digit), or the Request-URI domain not matching the PBX local domain list. Check your inbound routes and verify the number format the carrier sends matches what your PBX expects.

What is the difference between SIP 404 and SIP 480?

SIP 404 Not Found means the user does not exist on the server — there is no record of that extension or DID. SIP 480 Temporarily Unavailable means the user exists but is not reachable right now — the phone is not registered, is in DND, or is offline. 404 requires fixing the routing or provisioning; 480 usually resolves when the endpoint registers.

Getting SIP 404 on your calls?

Paste your SIP trace into SIPSymposium. The analyzer checks Request-URI format, identifies domain mismatches, and flags routing failures causing 404 responses.

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