GVPE.OSDEP(5)

NAME
gvpe.osdep - os dependent information

DESCRIPTION
This file tries to capture OS-dependent configuration or build issues, quirks and platform limitations, as known.

TUN vs. TAP interface
Most operating systems nowadays support something called a tunnel-device, which makes it possible to divert IPv4 (and often other protocols, too) into a user space daemon like gvpe. This is being referred to as a TUN-device.

This is fine for point-to-point tunnels, but for a virtual ethernet, an additional ethernet header is needed. This functionality (called a TAP device here) is only provided by a subset of the configurations.

On platforms only supporting a TUN-device, gvpe will invoke it's magical ethernet emulation package, which currently only handles ARP requests for the IPv4 protocol (but more could be added, bu the tincd network drivers might need to be modified for this to work). This means that on those platforms, only IPv4 will be supported.

Also, since there is no way (currently) to tell gvpe which IP subnets are found on a specific host, you will either need to hardwire the MAC address for TUN-style hosts on all networks (and avoid ARP altogether, which is possible), or you need to send a packet from these hosts into the vpn network to tell gvpe the local interface address.

Interface Initialisation
Unless otherwise notes, the network interface will be initialized with the expected MAC address and correct MTU value. With most interface drivers, this is done by running /sbin/ifconfig, so make sure that this command exists.

Interface Types

  native/linux
TAP-device; already part of the kernel (only 2.4+ supported, but see tincd/linux). This is the configuration tested best, as gvpe is being developed on this platform.

ifname should be set to the name of the network device.

To hardwire ARP addresses, use iproute2 (arp can do it, too):

  MAC=fe:fd:80:00:00:$(printf "%02x" $NODEID)
  ip neighbour add 10.11.12.13 lladdr $MAC nud permanent dev $IFNAME

  tincd/linux
TAP-device; already part of the kernel (2.2 only). See native/linux for more info.

ifname should be set to the path of a tap device, e.g. /dev/tap0. The interface will be named accordingly.

  native/cygwin
TAP-device; The TAP device to be used must either be the CIPE driver (http://cipe-win32.sourceforge.net/), or (highly recommended) the newer TAP-Win32 driver bundled with openvpn (http://openvpn.sf.net/). Just download and run the openvpn installer. The only option you need to select is the TAP driver.

ifname should be set to the name of the device, found in the registry at (no kidding :):

      HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Network\{4D36E972-E325-11CE-BFC1-08002BE10318}\<adapterid>\Connection\Name

The MAC address is dynamically being patched into packets and ARP-requests, so only IPv4 works with ARP on this platform.

  tincd/bsd
TAP-device, maybe; might work for many bsd variants.

This driver is a newer version of the tincd/*bsd drivers. It might provide a TAP device, or might not work at all. You might try this interface type first, and, if it doesn't work, try one of the OS-specific drivers.

  tincd/freebsd
TAP-device; part of the kernel (since 4.x, maybe earlier).

ifname should be set to the path of a tap device, e.g. /dev/tap0. The interface will be named accordingly.

These commands might be helpful examples:

  ifconfig $IFNAME 10.0.0.$NODEID
  route add -net 10.0.0.0 -netmask 255.255.255.0 -interface $IFNAME 10.0.0.$NODEID

  tincd/netbsd
TUN-device; The interface is a point-to-point device. To initialize it, you currently need to configure it as a point-to-point device, giving it an address on your vpn (the exact address doesn't matter), like this:

  ifconfig $IFNAME mtu $MTU up
  ifconfig $IFNAME 10.11.12.13 10.55.66.77
  route add -net 10.0.0.0 10.55.66.77 255.0.0.0
  ping -c1 10.55.66.77 # ping once to tell gvpe your gw ip

The ping is required to tell the ARP emulator inside GVPE the local IP address.

ifname should be set to the path of a tun device, e.g. /dev/tun0. The interface will be named accordingly.

  tincd/openbsd
TUN-device; already part of the kernel. See tincd/netbsd for more information.

  native/darwin
TAP-device;

The necessary kernel extension can be found here:

  http://www-user.rhrk.uni-kl.de/~nissler/tuntap/

There are two drivers, the one to use is the "tap" driver. It driver must be loaded before use, read the docs on how to install it as a startup item.

ifname should be set to the path of a tap device, e.g. /dev/tap0. The interface will be named accordingly.

These commands might be helpful examples:

  ifconfig $IFNAME 10.0.0.$NODEID
  route add -net 10.0.0.0 -interface $IFNAME 255.255.255.0

  tincd/darwin
TUN-device; See tincd/netbsd for more information. native/darwin is preferable.

The necessary kernel extension can be found here:

  http://chrisp.de/en/projects/tunnel.html

ifname should be set to the path of a tun device, e.g. /dev/tun0. The interface will be named accordingly.

The driver must be loaded before use:

  kmodload tunnel

  tincd/solaris
TUN-device; already part of the kernel(?), or available here:

  http://vtun.sourceforge.net/tun/

Some precompiled tun drivers might be available here:

  http://www.monkey.org/~dugsong/fragroute/

The interface MAC and MTU are NOT set up for you. Please try it out and send me an ifconfig command invocation that does that.

See tincd/netbsd for more information.

Completely untested so far.

  tincd/mingw
TAP-device; see native/cygwin for more information.

The setup is likely to be similar to native/cygwin.

Completely untested so far.

  tincd/raw_socket
TAP-device; purpose unknown and untested, probably binds itself on an existing ethernet device (given by ifname). It must be down prior to running the command, and GVPE will try to set it's MAC address and MTU to the "correct" values.

Completely untested so far.

  tincd/uml_socket
TAP-device; purpose unknown and untested, probably creates a UNIX datagram socket (path given by ifname) and reads and writes raw packets, so might be useful in other than UML contexts.

No network interface is created, and the MAC and MTU must be set as appropriate on the other side of the socket. GVPE will exit if the MAC address doesn't match what it expects.

Completely untested so far.

  tincd/cygwin
Known to be broken, use native/cygwin instead.

SEE ALSO
gvpe(5).

AUTHOR
Marc Lehmann <gvpe@schmorp.de>