Cellular Network Infrastructure » Core Network (CN) » OsmoGGSN (former OpenGGSN) » Linux Kernel GTP-U

h1. Basic Testing

This page documents some basic testing setup for the Kenrel GTP-U code. It follows the below rationale:

* focus on testing the kernel GTP-U module without too much external dependencies

* test GTP-U interoperability of the kernel with at least one other implementation, not just kernel-to-kernel (which currently is not supported in the kernel, as it only implements the GGSN/P-GW role)

* limit testing to SGSN/S-GW and GGSN/P-GW, without a real cellular network (which is possible e.g. using [[OsmoSGSN:]] and [[OsmoPCU:]])

h2. Building / Installing dependencies

In order to follow below test instructions, you will need

* A Linux kernel including the GTP-U driver (@drivers/net/gtp.c@) either compiled-in or as kernel module

* [[libgtpnl]] - the userspace library providing an API around the kernel GTP-U netlink interface

* [[OpenGGSN:]] - a minimal C-language implementation of a 3GPP GGSN, also contains a SGSN-side emulator called [[OpenGGSN:sgsnemu]]

You can find some instructions on how to build [[OpenGGSN:]] with support for [[libgtpnl]] and kernel GTP-U at this wiki page: [[OpenGGSN:Kernel_GTP]]

h2. Test setup description

We will run the GGSN natively on the host, and put the emulated SGSN inside a separate network namespace.

The two namespaces are interconnected by a virtual ethernet device using the transfer network 172.31.1.0/24

The GGSN is configured to provide a pool of IP addresses from the 192.168.71.0/24 range.  Each PDP context will be allocated one dynamic address from that pool

h2. Test instructions

h3. create the network namespace for the SGSN

 ip netns add sgsn

h3. add veth to be used between SGSN and GGSN

 ip link add veth0 type veth peer name veth1

h3. remote (SGSN) side of veth device

<pre>

ip link set veth1 netns sgsn

ip netns exec sgsn ip addr add 172.31.1.2/24 dev veth1

ip netns exec sgsn ip link set veth1 up

</pre>

h3. local (GGSN) side of veth device

<pre>

ip addr add  172.31.1.1/24 dev veth0

ip link set veth0 up

</pre>

h3. execute the GGSN on the host

 ggsn -g -c ./ggsn.conf.test

(use the file attached to this wiki page)

The @-g@ option is responsible for activating kernel-GTP support. If you cannot get the example described in this document to work, try the pure GTP-U userspace implementation by removing @-g@ from the above command line.  If it works then, there's something related to Kernel GTP-U that breaks the setup.

h3. execute the emulated SGSN inside the sgsn namespace

 ip netns exec sgsn sgsnemu -d -r 172.31.1.1 -l 172.31.1.2 --defaultroute --createif

h3. verify the existnace of the GTP tunnel

<pre>

ggsn:~# gtp-tunnel list

version 1 tei 1/1 ms_addr 192.168.71.2 sgsn_addr 172.31.1.2

</pre>

h3. further testing

in the @sgsn@ namespace, there's now a default-route that points into the GTP tunnel. You can use this to ping any network address that's reachable to the GGSN host.  If that host is connected to the internet, you can e.g. run a ping command from within the namespace using 

 ip netns exec sgsn ping -c 10 8.8.8.8

which will send some IP packets to 8.8.8.8 via the tun0 device (created by [[OpenGGSN:sgsnemu]]). It will be encapsulated by the userspace GTP-U implementation of sgsnemu, sent via the veth device to the host, where it ends up inthe GTP-U kernel module, decapsulating the package and passing in on to the gtp0 device there.  Anything beyond that point depends on your local routing configuration.