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
This commit is contained in:
Harald Welte 2017-10-12 21:37:48 +08:00 committed by Neels Hofmeyr
parent a4cb02699e
commit 3ce5a3648a
1 changed files with 44 additions and 8 deletions

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@ -246,26 +246,62 @@ OsmoGGSN(config-ggsn-apn)# shutdown <5>
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
----
[NetDev]
Name=ggsn
Name=apn0 <1>
Kind=tun
[Tun]
User=username
Group=username
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
----
[Match]
Name=ggsn
Name=apn0 <1>
[Network]
Address=192.168.7.1
IPMasquerade=yes
Address=192.168.7.1 <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 @@ ggsn ggsn0
gtp bind-ip 127.0.0.6
apn internet
gtpu-mode tun
tun-device ggsn
tun-device apn0
type-support v4
ip prefix dynamic 192.168.7.0/24
ip dns 0 192.168.100.1