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Re: [Linphone-users] hoping for help in protocol analyzation


From: Boris
Subject: Re: [Linphone-users] hoping for help in protocol analyzation
Date: Tue, 5 Oct 2021 12:02:35 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0


Hej again Dennis,

here i am again with some more things to report.

Finally, with all circumstances in mind, I do believe that it should be possible to make linphone work without changing the network environment or adding a network service like siproxd.

So I am focussing on the working hardphone Panasonic KX-UT133 in the first step.

Am 23.09.21 um 22:17 schrieb Boris:
Hej Dennis,

thanks for your hints. This is so much, I will need some time to follow....

Am 22.09.21 um 18:19 schrieb Dennis Filder:
It would be very interesting to know how these other SIP clients learn
the public IP address.  LEAF has tcpdump, so it should be easy to
figure out.  I suspect that they contact a hard-coded publically
reachable STUN server or do other tricks like that.


I tcpdumped the LAN and WAN interfaces of the leaf-box during initialization of the hardphone. And in fact, there is a response from cx.dtst.de that contains like SIP Status 200 OK and it contains the public IP.
As far as I understand, there is no STUN server within that communication.

I did't publish the pcap files for they seem to contain some private data. So, if needed, I could send them with PM or so....


As for TNG working and DT not working I assume that TNG is your ISP

yes

which means it can rewrite your outgoing SIP packets on the fly at the
next hop with a transparent SIP proxy because it knows both your phone
number and your currently assigned IP address.  I read about Telekom
doing it this way, and while it sure is convenient it isn't really how
SIP was intended to be used because it usually also allows any
stranger walking into your home to plug in an IP phone and perform
calls on your bill without having to authenticate against the SIP
provider.

No. I got some (one for each phone number) credentials from TNG to authorizw against their SIP server.

If SIP packets would be rewritten, LinPhone, Twinkle and the Panasonic HardPhone wouldn't be able to reach the DT server?

That's something to keep in mind.  It also gives people
wrong ideas about how SIP is designed to work.

I obviously belong to exactly these people - regardless of who or what is responsible for this.


What do you think could be the next step?

Thanks and regards,


Boris



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