Hi Christian,
you are right, it is missing in the generated OPTIONS from nathelper. It needs to be
added in the respective code part probably.
Cheers,
Henning Westerholt
-----Original Message-----
From: Christian Schnell via sr-users <sr-users(a)lists.kamailio.org>
Sent: Donnerstag, 23. November 2023 13:41
To: sr-users(a)lists.kamailio.org
Cc: Christian Schnell <cs(a)rekoba.de>
Subject: [SR-Users] Max-Forwards header missing in OPTIONS keep-alive
messages
Hello,
in RFC 3261 (sec. 8.1.1.6) it states about the Max-Forwards header field:
A UAC MUST insert a Max-Forwards header field
into each request it
originates with a value that SHOULD be 70.
When Kamailio sends its OPTIONS keep-alive requests (from the nathelper
module I believe), Max-Forwards is missing:
OPTIONS sip:alice@example.com:61266 SIP/2.0
Via: SIP/2.0/UDP aa.bb.cc.dd:5060;branch=z9hG4bK5124450
From:
sip:pinger@sip.example.com;tag=uloc-6550aa14-7456-2461-6390f173-
5fdb46
67
To: sip:alice@example.com:61266
Call-ID: aba25282-2ca72be1-9d1fd53(a)aa.bb.cc.dd
CSeq: 1 OPTIONS
Content-Length: 0
The user agent library I'm using (libre from baresip) rejects these requests with
a "400 Bad Request" response, I looked at the sources and it denies these
requests because of the missing Max-Forwards header.
Of course this suffices for the keep-alive logic because all that's needed is any
traffic in both directions to keep both (potential) NATs open. However you
might agree that it does look a bit confusing at first, and the RFC is clear about
that.
So it's not a bug, but is this behavior intended?
Thanks, also thanks for all the great work that has been put into Kamailio.
Christian
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