Re: Multiple double record routes in one BYE message

Hello,

interesting problem, I would expect that Kamailio removes the route header starting from the top and not in the middle. Just to clarify, are you seeing any error messages or warnings related to the rr module in the logs? Do you use one of the topology hiding modules?

Cheers,

Henning

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From: Ibe Van de Veire via sr-users <[email protected]>
Sent: Donnerstag, 19. Februar 2026 16:44
To: satyaprakash ch via sr-users <[email protected]>
Cc: Thomas Botte <[email protected]>; Ibe Van de Veire <[email protected]>
Subject: [SR-Users] Multiple double record routes in one BYE message

Dear Kamailio User Group,

I am working on a project that uses Kamailio as an SBC.
The SBC is configured as a multihomed device. It has an interface on the public side of the network and an interface on the internal (lan) side of the network.

I successfully configured the SBC to handle calls in all directions (ext to ext, int to ext, ext to int).
However, the call termination using BYE SIP messages does not seem to work in some situations.
When performing a call from an external device to another external device (hairpinning), the termination sent from the callee does not reach the caller.
Using sngrep, I can see the following flow for the BYE message:

  1.  BYE leaves callee
  2.  BYE is received by public interface of the sbc
  3.  BYE is passed to the private interface of the sbc
  4.  BYE is passed to the registrar on the internal network
  5.  BYE is passed back to the internal interface of the sbc
  6.  SBC responds with 404 not here

CALLEE            SBC (Public)      SBC (Private)        REGISTRAR
     |                    |                 |                   |
     |-------BYE--------->|                 |                   |
     |                    |                 |                   |
     |                    |~~~~(Internal)~~>|                   |
     |                    |                 |                   |
     |                    |                 |-------BYE-------->|
     |                    |                 |                   |
     |                    |                 |<------BYE---------|
     |                    |                 |                   |
     |                    |<~~~~(Internal)~~|                   |
     |                    |                 |                   |
     |<---404 Not Here----|                 |                   |
     |                    |                 |                   |

The bye message contains the following record routes in the first step:
Route: sip:6EAVHmFKfnIZxwFfgit29EJXQU1aMHI=@SBC_PUB_IP:62530;r2=on;lr;nat=yes
Route: sip:6EAVHmFKfnIZxwFfgit29EJXQU1aMHI=@SBC_LAN_IP;r2=on;lr;nat=yes
Route: sip:REGISTRAR_IP;lr;ftag=DomYqO1BCMhe-giL2X3KfBsMzgI7lEa9
Route: sip:SBC_LAN_IP;r2=on;lr;nat=yes
Route: sip:SBC_PUB_IP:62530;r2=on;lr;nat=yes

As you can see, the SBC uses double record routing to handle the multihomed setup.
In the next step (step2 -> step3), the SBC does remove two record routes, and the record route list looks as following:
Route: <sip:6EAVHmFKfnIZxwFfgit29EJXQU1aMHI=@SBC_LAN_IP;r2=on;lr;nat=yes>
Route: <sip:REGISTRAR_IP;lr;ftag=DomYqO1BCMhe-giL2X3KfBsMzgI7lEa9>
Route: <sip:SBC_LAN_IP;r2=on;lr;nat=yes>

The loose_route() function seems to remove the wrong pair from the list. I would expect the following output:
Route: sip:REGISTRAR_IP;lr;ftag=DomYqO1BCMhe-giL2X3KfBsMzgI7lEa9
Route: sip:SBC_LAN_IP;r2=on;lr;nat=yes
Route: sip:SBC_PUB_IP:62530;r2=on;lr;nat=yes

I feel like the rr module can not handle the multiple "double record routes" and matches the wrong entries.
RR does in fact recognize the SBC_LAN_IP as an "own IP" because in the last step, the last 2 parts of the double record routing are also removed.
Because all of this, in the last step, the internal interface of the SBC receives a BYE message without any record routes.
This results in a dead end.

Does someone know how I can tell Kamailio to remove the right pair of record routes.
Is there a workaround for this?
Am I doing something wrong?

Kind regards
Ibe Van de Veire
System Engineer
[email protected]<mailto:[email protected]>
Auguste Reyerslaan 52
B-1043 Brussel
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[VRT Banner]<https://www.bit.ly/VRTHandtekening>


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