GTP tunnel seems to exist, but No encapsulation when using libgtpnl

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Papa Tana papa.tana101 at gmail.com
Thu Aug 20 09:49:20 UTC 2020


Hi,

After successfully making libgtpnl works between 02 Linux Host, now I am in
the step of connecting one Linux Host to a real live SGSN this morning.

I don't have any particular issue at GTP-C side:

 - the Mobile Station registered on 3G network, requests one activate PDP
context to the SGSN
 - the SGSN sends to my ggsn a create PDP context
 - my ggsn accepts it, and answers with all the needed information, such as
MS_Address, DNS Address 1, DNS address 2, IP of GGSN-C, IP of GGSN-U, TEID
Control Plane, TEID user plane, .... everything should be OK.
 - upon receipt of my creade_pdp_context_response accepted, the SGSN now
try to establish a Tunnel with the given TEID towards my GGSN
 - but I cannot see anything on my GTPU-side in ggsn, apart of several
echo-request message from SGSN
 - Sure, SGSN try to test connectivity to my ggsn GTPU by using
echo-request, but no response
 - I don't know maybe because of no response, or because of SGSN alert me
with an error gtpu-sm-cause-update-ggsn-path-failure, the SGSN decide to
send a delete request

So I have 02 questions please:

 - 1) At GTP-C, I can implement all messages(echo-response,
create-response, delete-response) but at GTPU-side, as the port is used by
libgtpnl, I cannot implement an echo-response at all ==> So, do libgtpnl is
supposed to answer or not to an echo-response received from a SGSN at
GTPU-level?

 - 2) When I tried a Linux-to-Linux setup, it worked because I specified
the ms_addr and sgsn_addr in the 02 Linux Host.
 But as I cannot configure anything about the tunnel at SGSN-side(done
automatically by SGSN), I can only create the tunnel at ggsn-side thanks to
my user space program, by passing the TEID and ms_addr input to libgtpnl.
Does it mean that libgtpnl only complies with OpenGGSN, ergw, and
OpenAirInterface but not intended to ber used with a real SGSN?

Thanks for clarifying me,
Best Regards,


Le lun. 10 août 2020 à 23:00, Harald Welte <laforge at osmocom.org> a écrit :

> Hi Papa,
>
> On Sat, Aug 08, 2020 at 10:59:24AM +0300, Papa Tana wrote:
> > It is working now.
> > Very simple and stupid mistake from my side at network namespace
> configuration.
>
> I'm very happy to hear it's working successfully.  Sometimes I start to
> doubt
> if there are problems in the codebase, but the fact that you report you
> got it
> to work is a relief in that regard :)
> --
> - Harald Welte <laforge at osmocom.org>
> http://laforge.gnumonks.org/
>
> ============================================================================
> "Privacy in residential applications is a desirable marketing option."
>                                                   (ETSI EN 300 175-7 Ch.
> A6)
>
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