[PATCH] osmo-gsm-manuals[master]: GGSN: Document how 'ip tuntap' is used for non-root; call ne...

Harald Welte gerrit-no-reply at lists.osmocom.org
Sat Oct 14 05:34:26 UTC 2017

Hello Jenkins Builder,

I'd like you to reexamine a change.  Please visit


to look at the new patch set (#3).

GGSN: Document how 'ip tuntap' is used for non-root; call netdev 'apn0'

* Some people want to manually create/configure their tun devices,
  show them how to do this using ip with the correct parameters
* Let's not call the network device 'ggsn' but rather 'apn0', as
  the device has a 1:1 correspondence to the APN, not to the GGSN.

Change-Id: I2fef818bfcb8cb521397136539f492922d5f6def
M OsmoGGSN/chapters/configuration.adoc
1 file changed, 44 insertions(+), 8 deletions(-)

  git pull ssh://gerrit.osmocom.org:29418/osmo-gsm-manuals refs/changes/33/4233/3

diff --git a/OsmoGGSN/chapters/configuration.adoc b/OsmoGGSN/chapters/configuration.adoc
index 9e07fb6..9a4c81b 100644
--- a/OsmoGGSN/chapters/configuration.adoc
+++ b/OsmoGGSN/chapters/configuration.adoc
@@ -246,26 +246,62 @@
 It's possible to run OsmoGGSN without root privileges if the tun devices are already configured.
-.Example: device config via systemd-networkd using ggsn.netdev
+The interface creation + configuration must then happen before osmo-ggsn starting up.  This can be
+achieved by means such as
+* a custom shell script run as root before starting osmo-ggsn (e.g. as init script)
+* systemd .netdev and .network files
+==== Manual TUN device creation / configuration
+If you chose to go for custom shell/init scripts, you may use the `ip` program which is the standard
+tool for network interface configuration on Linux, part of the `iproute2` package.  In order to
+create a tun device, you must call it like this:
+.Example: iproute2 command to create a tun device
+# ip tuntap add dev apn0 mode tun user username group groupname
+Where _username_ and _groupname_ correspond to the User and Group that will have ownership over the
+device, i.e. the privileges which you intend to run osmo-ggsn under, and _apn0_ will be the
+name of the network device created.  After creating the interface, you can configure its addresses
+using standard means like `ip addr add` or your distribution-specific utilities/tools.
+==== systemd based TUN device creation+configuration
+If you want to have systemd take care of creating and configuring a tun device for you,
+you can use the below example config files.
+.Example: device config via systemd-networkd using apn0.netdev
+Name=apn0 <1>
+User=username <2>
+Group=username <3>
+<1> The network interface name of the newly-created device
+<2> The username under which you will run OsmoGGSN
+<3> The group name under which you will run OsmoGGSN
 .Example: network settings via systemd-networkd using ggsn.network
+Name=apn0 <1>
+Address= <2>
+IPMasquerade=yes <3>
+<1> The netowrk device name, which must match the one in the apn0.netdev unit file above
+<2> The local IP address configured on the device
+<3> Requesting systemd to configure IP masquerading for this interface.  Depending on your needs,
+    You may not want this if you have proper end-to-end routing set up, and want to have transparent
+    inbound IP access to your GPRS-attached devices.
 The pair of the configuration files above allows you to create and configure tun device which can be
 used by OsmoGGSN as follows.
@@ -277,7 +313,7 @@
  gtp bind-ip
  apn internet
   gtpu-mode tun
-  tun-device ggsn
+  tun-device apn0
   type-support v4
   ip prefix dynamic
   ip dns 0

To view, visit https://gerrit.osmocom.org/4233
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I2fef818bfcb8cb521397136539f492922d5f6def
Gerrit-PatchSet: 3
Gerrit-Project: osmo-gsm-manuals
Gerrit-Branch: master
Gerrit-Owner: Harald Welte <laforge at gnumonks.org>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: Max <msuraev at sysmocom.de>
Gerrit-Reviewer: Pau Espin Pedrol <pespin at sysmocom.de>

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