Re: Kamailio behind NAT

I did the suggested changes, I think. But the INVITE sent from Kamailio to Asterisk still holds the external advertised DNS in the RR.

Here’s the INVITE sent to Asterisk from Kamailio:

eth1  Out IP 10.3.124.192.5060 > 10.2.5.206.5080: SIP: INVITE sip:[email protected] SIP/2.0
INVITE sip:[email protected] SIP/2.0
Record-Route: <sip:sbc.coolcompany.com;lr;ftag=5914da19-6958-4b8f-b521-d74c78af6120>
Record-Route: <sip:sip-provider.com;lr=on>
Call-ID: [email protected]
CSeq: 25896 INVITE
From: <sip:[email protected]>;tag=5914da19-6958-4b8f-b521-d74c78af6120
To: <sip:[email protected]>
Contact: <sip:[email protected]:5080>
Via: SIP/2.0/UDP sbc.coolcompany.com:5060;branch=z9hG4bKb32c.739784aeb0177ad4d3e181098a071abb.0;rport
Via: SIP/2.0/UDP sip-provider.com;branch=z9hG4bKb32c.79821495565acb8af61a7ebecb22b26d.0
Via: SIP/2.0/UDP sip-provider.com:5060;branch=z9hG4bK-323035-3a9c396118a108606e6234ff3013ed5b
Max-Forwards: 67
Content-Type: application/sdp
User-Agent: XXXX
Content-Length: 293


Asterisk attempts to reply to the BYE on the external IP:

<--- Transmitting SIP request (616 bytes) to UDP:sbc.coolcompany.com:5060 --->
BYE sip:[email protected]:5080 SIP/2.0
Via: SIP/2.0/UDP 10.2.5.206:5080;rport;branch=z9hG4bKPj917dd0c5-192b-457d-ae1a-ef693895e0c7
From: <sip:[email protected]>;tag=1f88f783-83a4-419f-a7c3-3c37a40dada6
To: <sip:[email protected]>;tag=3c6c6d47-8beb-4c71-a829-15138869defd
Call-ID: [email protected]
CSeq: 25915 BYE
Route: <sip:sbc.coolcompany.com;lr;ftag=3c6c6d47-8beb-4c71-a829-15138869defd>
Route: <sip:x.x.x.x;lr>
Reason: Q.850;cause=16
Max-Forwards: 70
User-Agent: xxxx
Content-Length:  0



Here’s again my dumbed down CFG with changes:

debug=2
log_stderror=yes
fork=yes
tcp_accept_no_cl=yes
onsend_route_reply=yes
pv_buffer_size=2048
enable_tls=1


listen=udp:<LOCAL_IP>:5060 advertise <DOMAIN>:5060
listen=tcp:<LOCAL_IP>:5060 advertise <DOMAIN>:5060
listen=tls:<LOCAL_IP>:5061 advertise <DOMAIN>:5061

# INFO: Asterisk gateway listening
listen=udp:<LOCAL_IP>:5080
listen=tcp:<LOCAL_IP>:5080
listen=tls:<LOCAL_IP>:5081

local_rport=on

mpath="/usr/local/lib/kamailio/modules_k/:/usr/lib/x86_64-linux-gnu/kamailio/modules/"

loadmodule "rr.so"

modparam("rr", "force_send_socket", 1)

route {

                route(FROM_PROVIDER);
                exit;

}

route[RELAY] {

                if(!t_relay()) {

                                sl_reply_error();

                }

                exit;

}

route[FROM_PROVIDER] {

                # INFO: The Asterisk
                ds_select_dst(100, 4);

                if(!has_totag()) {
                                record_route();
                }

                route(RELAY);
                exit;

}


/M

From: Martin Nyström <[email protected]>
Date: Wednesday, 3 September 2025 at 10:59
To: [email protected] <[email protected]>, Kamailio (SER) - Users Mailing List <[email protected]>
Subject: Re: [SR-Users] Kamailio behind NAT
Using a different port for Asterisk is not a bad idea. I might just try that. I will return with the results or any follow up questions.



/M

From: Daniel-Constantin Mierla <[email protected]>
Date: Wednesday, 3 September 2025 at 10:54
To: Kamailio (SER) - Users Mailing List <[email protected]>
Cc: Martin Nyström <[email protected]>
Subject: Re: [SR-Users] Kamailio behind NAT

CAUTION: This email originated from outside the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.

Hello,

the simplest way is to listen on another port (e.g., 5080) and use that socket to communicate with Asterisk. For that listen parameter, do not set the advertise address. You can use $fs or force_send_socket() to specify the socket to be used for sending out to Asterisk.

The alternative is to play in the config file with the function of the rr module that allow you to set the address in the Record-/Route headers, but it may increase the complexity of the config.

Cheers,
Daniel

On 03.09.25 10:42, Martin Nyström via sr-users wrote:
Hello,

I am not successful in my attempts to configure my Kamailio to work behind NAT.

The flow of an incoming call is Provider (Internet) -> AWS LoadBalancer -> Kamailio -> Asterisk

Both the Kamailio and Asterisk is on the internal network. The issue I am having is that I need to add Record-Route to the traffic sent back towards the provider, but not to the Asterisk. Currently when I add the record_route() the header is sent to Asterisk which makes it reply to the Kamailio advertised external address for ACKs, BYEs etc.

I have dumbed down my Kamailio config as much as possible for this, to show what I am currently doing.


debug=2
log_stderror=yes
fork=yes
tcp_accept_no_cl=yes
onsend_route_reply=yes
pv_buffer_size=2048
enable_tls=1

listen=udp:<LOCAL_IP>:5060 advertise <EXTERNAL_DOMAIN>:5060
listen=tcp:<LOCAL_IP>:5060 advertise <EXTERNAL_DOMAIN>:5060
listen=tls:<LOCAL_IP>:5061 advertise <EXTERNAL_DOMAIN>:5061

local_rport=on

mpath="/usr/local/lib/kamailio/modules_k/:/usr/lib/x86_64-linux-gnu/kamailio/modules/"

# MODULES
loadmodule "..."

route {

                route(FROM_PROVIDER);

}


route[RELAY] {

                if(!t_relay()) {

                                sl_reply_error();

                }

                exit;

}

route[FROM_PROVIDER] {

               # The Asterisk that should not receive the external dns in the record route header
                ds_select_dst(100, 4);

                # INFO: This adds the Record-Route in all directions
                if(!has_totag()) {
                                record_route();
                }

                route(RELAY);
                exit;

}





/M


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Daniel-Constantin Mierla (@ asipto.com)

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Kamailio Consultancy, Training and Development Services -- asipto.com

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Important: keep the mailing list in the recipients, do not reply only to the sender!