Interfering with the GTP-u Kernel module

Thomas Boros tomas.boros92 at
Fri Feb 16 08:00:22 UTC 2018

Hi Harald,

I’ve also noticed one unusual thing. I noticed, that the the gtp-link app must be running, so the socket remains open. If I kill the application and I have gtp-tunnels set up, the machine responds with and ICMP port unreachable message, but I suppose, this behaviour is ok. Another issue I’ve noticed, I’ve enabled module debugging and I can clearly see, if there is a GTP datagram arriving on the socket to a pdp context, which is not existing, the log says that the datagram is going to be handled in the userspace. However, even if the gtp-link tool is running, the datagrams are not passed to the userspace, they get buffered in the Recieve-Q (checked via netstat). On each packet this queue gets larger, what I assume is not the desired functionality. I guess there is something wrong with the gtp-link tool. Did you encounter such situation? I’m using the latest kernel 4.15.3 and the library is compiled from the osmocom repository.

root at gtpt:~# uname -ar
Linux gtpt 4.15.3-041503-generic #201802120730 SMP Mon Feb 12 07:31:14 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux


> On 16 Feb 2018, at 08:24, Harald Welte <laforge at> wrote:
> Hi Thomas,
> On Thu, Feb 15, 2018 at 11:06:12AM +0100, Thomas Boros wrote:
>> +bin_PROGRAMS = gtp-link                        \
>> +               gtp-tunnel
>> +
>> check_PROGRAMS = gtp-link              \
>>                 gtp-tunnel
> This would have them both in bin_PROGRAMS and in check_PROGRAMS, which is redundant.
> In any case bin_PROGRAMS installs those tools, which are really only useful to developers
> and not for the typical users.  I went for an alternative and included them in noinst_PROGRAMS,
> i.e. they are always being built during 'make' not only 'make check', but they still aren't
> installed during 'make install'.
> See
> -- 
> - Harald Welte <laforge at> 
> ============================================================================
> "Privacy in residential applications is a desirable marketing option."
>                                                  (ETSI EN 300 175-7 Ch. A6)

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