Hello,

can you send a pcap with a call reproducing such case? I can check it with the c code and see if something is mismatched.

Cheers,
Daniel

On 09.06.20 13:00, George Diamantopoulos wrote:

Hello again,

This might turn out to be a bug, but I'm posting here first because my config is fairly complicated and it might not be the sanest it could be. The problem manifests as follows: with the sole change being the enabling of track_cseq_updates for the dialog module, kamailio fails to process the 100 Trying it receives following authentication initiated by the uac_auth() function. Without the track_cseq_updates option enabled, the call proceeds successfully, albeit with the CSeq for the auth-carrying INVITE having the same value as the original.

Here's a simplified version of the configuration routes involved in this:

request_route {
    ...
    route(DISPATCH_PROVIDER);
    ...
}

route[DISPATCH_PROVIDER] {
    if ( !ds_select_dst("10", "8") ) {
        t_send_reply("503", "Downstream carrier unavailable");
        exit;
    }

    t_on_branch_failure("DISPATCH_PROVIDER_FAILOVER");
    t_on_branch("PROVIDER_BRANCH");
    t_on_failure("DISPATCH_PROVIDER_FAILURE");

    route(RELAY);
    exit;
}

failure_route[DISPATCH_PROVIDER_FAILURE] {
    if (t_is_canceled()) {
        exit;
    }
    if ( t_check_status("401|407") ) {
        $avp(arealm) = "authrealm.com";
        $avp(auser) = "authusername";
        $avp(apass) = "verys3kr1t";
        uac_auth();

        t_on_branch("PROVIDER_BRANCH");
        t_on_branch_failure("DISPATCH_PROVIDER_FAILOVER");
        t_on_failure("DISPATCH_PROVIDER_FAILURE");

        $du = "sip:" + $T_rpl($si) + ":" + $T_rpl($sp); // I'll explain why this is here later in this e-mail
        t_relay();
        exit;
    }
}

branch_route[PROVIDER_BRANCH] {
    uac_replace_from("$dlg_var(my_new_from)");
    uac_replace_to("$dlg_var(my_new_to)");
    $rU = "my new RURI user";
}

event_route[tm:branch-failure:DISPATCH_PROVIDER_FAILOVER] {
    if (t_is_canceled()) {
        exit;
    }
    if ( t_check_status("401|407") ) {
        return;
    # next DST - only for 5xx or local timeout
    } else if ( t_check_status("5[0-9][0-9]") || (t_branch_timeout() && !t_branch_replied()) ) {
        if ( ds_next_dst() ) {
            t_on_branch("PROVIDER_BRANCH");
            t_on_branch_failure("DISPATCH_PROVIDER_FAILOVER");
            t_on_failure("DISPATCH_PROVIDER_FAILURE");
            route(RELAY);
            exit;
        } else {
            xlog("L_NOTICE", "--- SCRIPT_DISPATCH_PROVIDER_FAILOVER: Failed to route request to PROVIDER! Giving Up. Negative response will be sent upstream.\n");
        }
    }
}

One will rightfully wonder why use both branch-failure routes and failure_route to handle things. Well, it's not obvious from this because the relevant parts are removed for brevity, but I'm generally using branch failure event routes to try other destinations in the same destination set, and failure routes to additionally try other downstream "providers" in case all entries is the current destination set have failed. I don't think these actions/routes are relevant because the problem manifests without any of these failover mechanisms (of switching over to the next provider) engaging.

Regarding the line "$du = "sip:" + $T_rpl($si) + ":" + $T_rpl($sp);" in the failure_route, which might seem a little odd, this was added because without it, uac_auth() will send the auth-carrying INVITE always to the first destination in the destination set even if ds_next_dst has been called from the branch-failure event route. Unfortunately I haven't been able to determine if this actually helped, because I have only received a 5xx error once from the downstream peer before the "fix" and haven't been able to reproduce this since then. But that's another issue unrelated to the one I'm asking about here.

So what happens with track_cseq_updates enabled is, after uac_auth() successfully sends the authenticated INVITE and the peer starts sending provisional responses, kamailio doesn't seem to acknowledge them. Instead, it will retransmit the auth INVITE as if there was a firewall preventing the 1xx responses from being admitted. Then, the timeout will engage and the configuration script will behave as if t_branch_timeout returns true (it will do ds_next_dst).

So I was wondering if this is to be expected with this configuration, or if this should be reported as a bug. Thanks!

Best regards,

George

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