Re: Intermittent S-CSCF → HSS Diameter Connec tion Failure - CER Not Sent After TCP Connect

Hey Qasim,

this might be an issue with the Diameter peer state-machine, or maybe the
state is set wrongly. To debug it further, you could try to:
- enable debug in the logs - e.g. would be interesting to see what this
line says, if it is even triggered:
https://github.com/kamailio/kamailio/blob/master/src/modules/cdp/peerstatemachine.c#L95
- try to capture a pcap, to confirm the scenario, or the exact event
sequence here.

Cheers,
-Dragos

On Mon, Dec 29, 2025 at 6:42 AM Qasim Loay via sr-users <
[email protected]> wrote:

> Hello Kamailio Community,
>
>
>
> We're experiencing a *critical issue* in Kamailio where S-CSCF randomly
> stops sending CER to HSS in some cases after establishing TCP connections,
> causing complete authentication failures.
>
> Please find the attached (IMS containers + HSS )logs  and the current
> configuration.
>
>
>
> *Environment*
>
>    - *Kamailio Version:* kamailio 6.0.2 (x86_64/linux) d4dc5d
>    - *Deployment:* SCSCF and HSS as a container on same physical machine
>    using macvlan networking
>
> *Components:*
>
>    - SCSCF: 172.22.1.20
>    - HSS: 172.22.1.3
>    - ICSCF: 172.22.1.19
>
>
>
> *Problem Description*
>
> *The issue occurs randomly* - the system works normally for periods of
> time, then suddenly the Diameter connection between SCSCF and HSS fails and
> enters a reconnection seems loop.
>
>
>
> *Here's the cycle we're observing:*
>
>
>
> *1. *SCSCF: WARNING: cdp [peermanager.c:337]: peer_timer(): Inactivity on
> peer [hss.epc.mnc092.mcc418.3gppnetwork.org] and no DWA, Closing peer...
>
> *2. State Timeout (~40 seconds later):* S-CSCF: ERROR: cdp
> [peerstatemachine.c:164]: sm_process(): in state Closed timeout event
> Timeout
>
> *3. Reconnection Attempt (~30 seconds later):*
>
> SCSCF: INFO: cdp [peerstatemachine.c:551]: I_Snd_Conn_Req():  Peer
> hss.epc.mnc092.mcc418.3gppnetwork.org
>
> SCSCF: INFO: cdp [receiver.c:991]: peer_connect(): Trying to connect to
> 172.22.1.3 port 3870
>
> SCSCF: INFO: cdp [receiver.c:1090]: peer_connect(): Peer
> hss.epc.mnc092.mcc418.3gppnetwork.org:3870 connected
>
> *4. HSS Side (waiting indefinitely):*HSS: [hss:0.19.37] 2025/12/25
> 04:46:39.060208 [INF]  [scscf>hss:0][waiting for CER from
> 172.22.1.20:33284]
>
>
>
> *Cascading Effects:*
>
> *ICSCF accumulates branches:*
>
> ICSCF: ERROR: tm [t_fwd.c:792]: add_uac(): maximum number of branches
> exceeded
>
> ICSCF: ERROR: tm [t_fwd.c:1771]: t_forward_nonack(): failure to add
> branches
>
>
>
> *Result:* each UE cannot be able to register to IMS and VoLTE service
> outage for all UEs
>
>
> Best regards,
>
> Qasim Loay
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