Just to add a bit for an issue:

On a mobile client, Linphone in particular, system may be in state, that it "believes", that TCP connection still exists, but on a server (Kamailio) side it's already closed by tcp_keepalive_enable() option.

As I got, RST is not reaching mobile device (which is ok, I assume, in a mobile world).

But device due to "internal believes" sending the packets via already dead TCP connection and as a result, on outgoing call I'm getting 408 - Timeout.

Linphone developers suggested to use this CRLF method for keepalive, so I'm asking after finding traces of this RFC only in outbound module.

P.S.: I know, keepalive on TCP and mobile world is usually a bad idea, but maybe it's better in general than SIP OPTIONS ping. From my point of view, TCP stack state should be enough already, but reality is reality

Le jeu. 21 mars 2024 à 16:18, Ihor Olkhovskyi <igorolhovskiy@gmail.com> a écrit :

Julien,

Yes, I did. It just invokes setsockopt() from system library - https://linux.die.net/man/3/setsockopt

This one is a bit different.

Le jeu. 21 mars 2024 à 14:29, Julien Chavanton <jchavanton@gmail.com> a écrit :

Did you look at the tcpops module.

I am sometimes getting confused but I think this is the one made by the kernel and it is simply a socket option flag.

On Thu, Mar 21, 2024, 6:14 AM Ihor Olkhovskyi via sr-users <sr-users@lists.kamailio.org> wrote:

Hello,

A bit generic question, does Kamailio supports CRLF keepalive per https://www.rfc-editor.org/rfc/rfc5626#section-4.4.1 ?

It's more for tracking TCP connection states, as seems tcp_keepalive_enable is not super reliable especially in mobile networks.

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Best regards,
Ihor (Igor)

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Best regards,
Ihor (Igor)