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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: Thu, 23 Sep 2021 22:17:43 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0

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:
On Wed, Sep 22, 2021 at 11:28:46AM +0200, wrote:

Do I understand correct, that I have to use either a STUN server or
a local proxy to make LinPhone work fully?

If you sit behind a router that does NAT then yes.  LEAF apparently
offers a package named siproxd.lrp.  If you get that to work keep
detailed notes and consider writing a tutorial for the LEAF wiki.

I like to see that you seem to know LEAF. I'm using it since about 20 years (oops, I'm shocked) and seem to be quite familiar with it. If siproxd.lrp is the way to do it, I'll write the tutorial!

As far as I could research until now, DT doesn't serve STUN.

     $ host is an alias for has address has IPv6 address 2600:1f16:8c5:101::108

I have no idea what the privacy policy of that third party provider
is, though.  Maybe you can find more somewhere on exists, too.  Or maybe
you can run your own if you have a VPS.

OK, thanks. Some homework to do....

And a local proxy would possibly prevent a second SIP service from
being used on the LAN?

Not necessarily.  It will depend on how auto-configuration via
broadcast/zeroconf/Avahi/SRV records is done.  In theory you can use
as many different SIP servers and proxies on a network as you like,
but you will probably have to manually configure each client to use a
static configuration.

More facs from my local network:
a) The router is a full-configurable box based on APU Board with
LEAF-software (, which is a purified small Linux.....
b) There is a Panasonic KXsomething IP-Phone working all fine within the
local network against the DT.
c) LinPhone works fine as well against an other SIP-Provider (TNG).
d) The disconnection after 15 minutes doesn't happen with Twinkle as

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.

OK, more homework.... ;-)

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


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

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.


P.S.: Your reply to the list didn't make it through for some reason.

I found my reply in the list's archive, so it seems it was received?
I try to put that message back on the list.

Thanks very much an regards,


PS: I'll be back with replies to the technical hints - need some days.....

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