gvpe/doc/gvpe.texi

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@c %**start of header
@finalout
@setfilename gvpe.info
@settitle GNU Virtual Private Ethernet Manual
@setchapternewpage odd
@c %**end of header

@ifinfo
@dircategory Networking tools
@direntry
* gvpe: (gvpe).              The GNU VPE Manual.
@end direntry

This is the info manual for vpe, the Virtual Private Ethernet daemon.

Copyright @copyright{} 2003-2008 Marc Lehmann <gvpe@@schmorp.de>.

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

@end ifinfo

@titlepage
@title gvpe Manual
@author Marc Lehmann

@page
@vskip 0pt plus 1filll
@cindex copyright

Copyright @copyright{} 2003-2008 Marc Lehmann <gvpe@@schmorp.de>.

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

@end titlepage

@contents

@node Top,Overview,,(dir)

@chapter Introduction
This is the documentation for the GNU Virtual Private Ethernet suite.
@refill
The GNU Virtual Private Ethernet suite implements a virtual (uses udp, tcp, rawip and other protocols for tunneling), private (encrypted, authenticated) ethernet (mac-based, broadcast-based network) that is shared among multiple nodes, in effect implementing an ethernet bus over public networks.
@refill

@menu
* Overview::        Introduction to and Tutorial for GVPE (gvpe(5))
* OS Dependencies:: OS-Dependent Installation and Configuration Notes (gvpe.osdep(5))
* gvpe.conf::       The main configuration file (gvpe.conf(5))
* gvpectrl::        Configuration/Control Program Reference (gvpectrl(8))
* gvpe::            The GVPE Daemon (gvpe(8))
* gvpe.protocol::   The GVPE Transport and VPN Protocols (gvpe.protocol(7))
* Simple Example::  A simple yet realistic Example
* Complex Example:: A non-trivial Example
* Index::           Keyword and Concept index
@end menu


@node Overview,OS Dependencies,Top,Top

@chapter Overview

@section NAME
GNU-VPE - Overview of the GNU Virtual Private Ethernet suite.
@refill


@section DESCRIPTION
GVPE is a suite designed to provide a virtual private network for multiple nodes over an untrusted network. This document first gives an introduction to VPNs in general and then describes the specific implementation of GVPE.
@refill


@subsection WHAT IS A VPN?
VPN is an acronym, it stands for:
@refill


@itemize


@item
Virtual

Virtual means that no physical network is created (of course), but a network is @emph{emulated} by creating multiple tunnels between the member nodes by encapsulating and sending data over another transport network.
@refill
Usually the emulated network is a normal IP or Ethernet, and the transport network is the Internet. However, using a VPN system like GVPE to connect nodes over other untrusted networks such as Wireless LAN is not uncommon.
@refill


@item
Private

Private means that non-participating nodes cannot decode ("sniff)" nor inject ("spoof") packets. This means that nodes can be connected over untrusted networks such as the public Internet without fear of being eavesdropped while at the same time being able to trust data sent by other nodes.
@refill
In the case of GVPE, even participating nodes cannot sniff packets send to other nodes or spoof packets as if sent from other nodes, so communications between any two nodes is private to those two nodes.
@refill


@item
Network

Network means that more than two parties can participate in the network, so for instance it's possible to connect multiple branches of a company into a single network. Many so-called "VPN" solutions only create point-to-point tunnels, which in turn can be used to build larger networks.
@refill
GVPE provides a true multi-point network in which any number of nodes (at least a few dozen in practise, the theoretical limit is 4095 nodes) can participate.
@refill
@end itemize


@subsection GVPE DESIGN GOALS


@itemize


@item
SIMPLE DESIGN

Cipher, HMAC algorithms and other key parameters must be selected at compile time - this makes it possible to only link in algorithms you actually need. It also makes the crypto part of the source very transparent and easy to inspect, and last not least this makes it possible to hardcode the layout of all packets into the binary. GVPE goes a step further and internally reserves blocks of the same length for all packets, which virtually removes all possibilities of buffer overflows, as there is only a single type of buffer and it's always of fixed length.
@refill


@item
EASY TO SETUP

A few lines of config (the config file is shared unmodified between all hosts) and a single run of @t{gvpectrl} to generate the keys suffices to make it work.
@refill


@item
MAC-BASED SECURITY

Since every host has it's own private key, other hosts cannot spoof traffic from this host. That makes it possible to filter packet by MAC address, e.g. to ensure that packets from a specific IP address come, in fact, from a specific host that is associated with that IP and not from another host.
@refill
@end itemize


@section PROGRAMS
Gvpe comes with two programs: one daemon (@t{gvpe}) and one control program (@t{gvpectrl}).
@refill


@itemize


@item
gvpectrl

This program is used to generate the keys, check and give an overview of of the configuration and to control the daemon (restarting etc.).
@refill


@item
gvpe

This is the daemon used to establish and maintain connections to the other network nodes. It should be run on the gateway of each VPN subnet.
@refill
@end itemize


@section COMPILETIME CONFIGURATION
Please have a look at the @t{gvpe.osdep(5)} manpage for platform-specific information.
@refill
Gvpe hardcodes most encryption parameters. While this reduces flexibility, it makes the program much simpler and helps making buffer overflows impossible under most circumstances.
@refill
Here are a few recipes for compiling your gvpe, showing the extremes (fast, small, insecure OR slow, large, more secure), between which you should choose:
@refill


@subsection AS LOW PACKET OVERHEAD AS POSSIBLE


@example
   ./configure --enable-hmac-length=4 --enable-rand-length=0
@end example

Minimize the header overhead of VPN packets (the above will result in only 4 bytes of overhead over the raw ethernet frame). This is a insecure configuration because a HMAC length of 4 makes collision attacks based on the birthday paradox pretty easy.
@refill


@subsection MINIMIZE CPU TIME REQUIRED


@example
   ./configure --enable-cipher=bf --enable-digest=md4
@end example

Use the fastest cipher and digest algorithms currently available in gvpe. MD4 has been broken and is quite insecure, though, so using another digest algorithm is recommended.
@refill


@subsection MAXIMIZE SECURITY


@example
   ./configure --enable-hmac-length=16 --enable-rand-length=8 --enable-digest=sha1
@end example

This uses a 16 byte HMAC checksum to authenticate packets (I guess 8-12 would also be pretty secure ;) and will additionally prefix each packet with 8 bytes of random data. In the long run, people should move to SHA-256 and beyond).
@refill
In general, remember that AES-128 seems to be as secure but faster than AES-192 or AES-256, more randomness helps against sniffing and a longer HMAC helps against spoofing. MD4 is a fast digest, SHA1, RIPEMD160, SHA256 are consecutively better, and Blowfish is a fast cipher (and also quite secure).
@refill


@section HOW TO SET UP A SIMPLE VPN
In this section I will describe how to get a simple VPN consisting of three hosts up and running.
@refill


@subsection STEP 1: configuration
First you have to create a daemon configuration file and put it into the configuration directory. This is usually @t{/etc/gvpe}, depending on how you configured gvpe, and can be overwritten using the @t{-c} command line switch.
@refill
Put the following lines into @t{/etc/gvpe/gvpe.conf}:
@refill


@example
   udp-port = 50000 # the external port to listen on (configure your firewall)
   mtu = 1400       # minimum MTU of all outgoing interfaces on all hosts
   ifname = vpn0    # the local network device name

   node = first     # just a nickname
   hostname = first.example.net # the DNS name or IP address of the host

   node = second
   hostname = 133.55.82.9

   node = third
   hostname = third.example.net
@end example

The only other file necessary is the @t{if-up} script that initializes the virtual ethernet interface on the local host. Put the following lines into @t{/etc/gvpe/if-up} and make it executable (@t{chmod 755 /etc/gvpe/if-up}):
@refill


@example
   #!/bin/sh
   ip link set $IFNAME address $MAC mtu $MTU up
   [ $NODENAME = first  ] && ip addr add 10.0.1.1 dev $IFNAME
   [ $NODENAME = second ] && ip addr add 10.0.2.1 dev $IFNAME
   [ $NODENAME = third  ] && ip addr add 10.0.3.1 dev $IFNAME
   ip route add 10.0.0.0/16 dev $IFNAME
@end example

This script will give each node a different IP address in the @t{10.0/16} network.  The internal network (if gvpe runs on a router) should then be set to a subset of that network, e.g.  @t{10.0.1.0/24} on node @t{first}, @t{10.0.2.0/24} on node @t{second}, and so on.
@refill
By enabling routing on the gateway host that runs @t{gvpe} all nodes will be able to reach the other nodes. You can, of course, also use proxy ARP or other means of pseudo-bridging, or (best) full routing - the choice is yours.
@refill


@subsection STEP 2: create the RSA key pairs for all hosts
Run the following command to generate all key pairs for all nodes (that might take a while):
@refill


@example
   gvpectrl -c /etc/gvpe -g
@end example

This command will put the public keys into @t{/etc/gvpe/pubkeys/@emph{nodename}} and the private keys into @t{/etc/gvpe/hostkeys/@emph{nodename}}.
@refill


@subsection STEP 3: distribute the config files to all nodes
Now distribute the config files and private keys to the other nodes. This should be done in two steps, since only the private keys meant for a node should be distributed (so each node has only it's own private key).
@refill
The example uses rsync-over-ssh
@refill
First all the config files without the hostkeys should be distributed:
@refill


@example
   rsync -avzessh /etc/gvpe first.example.net:/etc/. --exclude hostkeys
   rsync -avzessh /etc/gvpe 133.55.82.9:/etc/. --exclude hostkeys
   rsync -avzessh /etc/gvpe third.example.net:/etc/. --exclude hostkeys
@end example

Then the hostkeys should be copied:
@refill


@example
   rsync -avzessh /etc/gvpe/hostkeys/first  first.example.net:/etc/hostkey
   rsync -avzessh /etc/gvpe/hostkeys/second 133.55.82.9:/etc/hostkey
   rsync -avzessh /etc/gvpe/hostkeys/third  third.example.net:/etc/hostkey
@end example

You should now check the configuration by issuing the command @t{gvpectrl -c /etc/gvpe -s} on each node and verify it's output.
@refill


@subsection STEP 4: starting gvpe
You should then start gvpe on each node by issuing a command like:
@refill


@example
   gvpe -D -l info first # first is the nodename
@end example

This will make the gvpe daemon stay in foreground. You should then see "connection established" messages. If you don't see them check your firewall and routing (use tcpdump ;).
@refill
If this works you should check your networking setup by pinging various endpoints.
@refill
To make gvpe run more permanently you can either run it as a daemon (by starting it without the @t{-D} switch), or, much better, from your inittab or equivalent. I use a line like this on all my systems:
@refill


@example
   t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1
@end example


@subsection STEP 5: enjoy
... and play around. Sending a -HUP (@t{gvpectrl -kHUP}) to the daemon will make it try to connect to all other nodes again. If you run it from inittab, as is recommended, @t{gvpectrl -k} (or simply @t{killall gvpe}) will kill the daemon, start it again, making it read it's configuration files again.
@refill


@section COPYRIGHTS AND LICENSES
GVPE itself is distributed under the GENERAL PUBLIC LICENSE (see the file COPYING that should be part of your distribution).
@refill
In some configurations it uses modified versions of the tinc vpn suite, which is also available under the GENERAL PUBLIC LICENSE.
@refill


@node OS Dependencies,gvpe.conf,Overview,Top

@chapter OS Dependencies

@section NAME
gvpe.osdep - os dependent information
@refill


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


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


@section 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 @t{/sbin/ifconfig}, so make sure that this command exists.
@refill


@section Interface Types


@subsection 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.
@refill
@t{ifname} should be set to the name of the network device.
@refill
To hardwire ARP addresses, use iproute2 (@t{arp} can do it, too):
@refill


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


@subsection tincd/linux
TAP-device; already part of the kernel (2.2 only). See @t{native/linux} for more info.
@refill
@t{ifname} should be set to the path of a tap device, e.g. @t{/dev/tap0}. The interface will be named accordingly.
@refill


@subsection native/cygwin
TAP-device; The TAP device to be used must either be the CIPE driver (@t{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.
@refill
@t{ifname} should be set to the name of the device, found in the registry at (no kidding :):
@refill


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

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


@subsection tincd/bsd
TAP-device, maybe; migth work for many bsd variants.
@refill
This driver is a newer version of the @t{tincd/*bsd} drivers. It @emph{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.
@refill


@subsection tincd/freebsd
TAP-device; part of the kernel (since 4.x, maybe earlier).
@refill
@t{ifname} should be set to the path of a tap device, e.g. @t{/dev/tap0}. The interface will be named accordingly.
@refill
These commands might be helpful examples:
@refill


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


@subsection 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:
@refill


@example
  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
@end example

The ping is required to tell the ARP emulator inside GVPE the local IP address.
@refill
@t{ifname} should be set to the path of a tun device, e.g. @t{/dev/tun0}. The interface will be named accordingly.
@refill


@subsection tincd/openbsd
TUN-device; already part of the kernel. See @t{tincd/netbsd} for more information.
@refill


@subsection native/darwin
TAP-device;
@refill
The necessary kernel extension can be found here:
@refill


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

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.
@refill
@t{ifname} should be set to the path of a tap device, e.g. @t{/dev/tap0}. The interface will be named accordingly.
@refill
These commands might be helpful examples:
@refill


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


@subsection tincd/darwin
TUN-device; See @t{tincd/netbsd} for more information. @t{native/darwin} is preferable.
@refill
The necessary kernel extension can be found here:
@refill


@example
  http://chrisp.de/en/projects/tunnel.html
@end example

@t{ifname} should be set to the path of a tun device, e.g. @t{/dev/tun0}. The interface will be named accordingly.
@refill
The driver must be loaded before use:
@refill


@example
  kmodload tunnel
@end example


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


@example
  http://vtun.sourceforge.net/tun/
@end example

Some precompiled tun drivers might be available here:
@refill


@example
  http://www.monkey.org/~dugsong/fragroute/
@end example

The interface MAC and MTU are @emph{NOT} set up for you. Please try it out and send me an @t{ifconfig} command invocation that does that.
@refill
See @t{tincd/netbsd} for more information.
@refill
Completely untested so far.
@refill


@subsection tincd/mingw
TAP-device; see @t{native/cygwin} for more information.
@refill
The setup is likely to be similar to @t{native/cygwin}.
@refill
Completely untested so far.
@refill


@subsection tincd/raw_socket
TAP-device; purpose unknown and untested, probably binds itself on an existing ethernet device (given by @t{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.
@refill
Completely untested so far.
@refill


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


@subsection tincd/cygwin
Known to be broken, use @t{native/cygwin} instead.
@refill


@node gvpe.conf,gvpectrl,OS Dependencies,Top

@chapter gvpe.conf

@section NAME
gvpe.conf - configuration file for the GNU VPE daemon
@refill


@section SYNOPSIS


@example
   # global options for all nodes
   udp-port = 407
   mtu = 1492
   ifname = vpn0

   # first node is named branch1 and is at 1.2.3.4
   node = branch1
   hostname = 1.2.3.4

   # second node uses dns to resolve the address
   node = branch2
   hostname = www.example.net
   udp-port = 500       # this host uses a different udp-port

   # third node has no fixed ip address
   node = branch3
   connect = ondemand
@end example


@section DESCRIPTION
The gvpe config file consists of a series of lines that contain @t{variable = value} pairs. Empty lines are ignored. Comments start with a @t{#} and extend to the end of the line. They can be used on their own lines, or after any directives. Whitespace is allowed around the @t{=} sign or after values, but not within the variable names or values themselves.
@refill
The only exception to the above is the "on" directive that can prefix any @t{name = value} setting and will only "execute" it on the named node, or (if the nodename starts with "!") on all nodes except the named one.
@refill
For example, set the MTU to @t{1450} everywhere, loglevel to @t{noise} on branch1, and connect to @t{ondemand} everywhere but on branch2:
@refill


@example
   mtu = 1450
   on branch1 loglevel = noise
   on !branch2 connect = ondemand
@end example

All settings are applied "in order", that is, later settings of the same variable overwrite earlier ones.
@refill


@section ANATOMY OF A CONFIG FILE
Usually, a config file starts with a few global settings (like the UDP port to listen on), followed by node-specific sections that begin with a @t{node = nickname} line.
@refill
Every node that is part of the network must have a section that starts with @t{node = nickname}. The number and order of the nodes is important and must be the same on all nodes. It is not uncommon for node sections to be completely empty - if the default values are right.
@refill
Node-specific settings can be used at any time. If used before the first node section they will set the default values for all following nodes.
@refill


@section CONFIG VARIABLES


@subsection GLOBAL SETTINGS
Global settings will affect the behaviour of the running gvpe daemon, that is, they are in some sense node-specific (config files can set different values on different nodes using @t{on}), but will affect the behaviour of the gvpe daemon and all connections it creates.
@refill


@itemize


@item
dns-forw-host = hostname/ip

@cindex dns-forw-host
The DNS server to forward DNS requests to for the DNS tunnel protocol (default: @t{127.0.0.1}, changing it is highly recommended).
@refill


@item
dns-forw-port = port-number

@cindex dns-forw-port
The port where the @t{dns-forw-host} is to be contacted (default: @t{53}, which is fine in most cases).
@refill


@item
dns-max-outstanding = integer-number-of-requests

@cindex dns-max-outstanding
The maximum number of outstanding DNS transport requests (default: @t{100}). GVPE will never issue more requests then the given limit without receiving replies. In heavily overloaded situations it might help to set this to a low number (e.g. @t{3} or even @t{1}) to limit the number of parallel requests.
@refill
The default should be working OK for most links.
@refill


@item
dns-overlap-factor = float

@cindex dns-overlap-factor
The DNS transport uses the minimum request latency (@strong{min_latency}) seen during a connection as it's timing base. This factor (default: @t{0.5}, must be > 0) is multiplied by @strong{min_latency} to get the maximum sending rate (= minimum send interval), i.e. a factor of @t{1} means that a new request might be generated every @strong{min_latency} seconds, which means on average there should only ever be one outstanding request.  A factor of @t{0.5} means that GVPE will send requests twice as often as the minimum latency measured.
@refill
For congested or picky DNS forwarders you could use a value nearer to or exceeding @t{1}.
@refill
The default should be working OK for most links.
@refill


@item
dns-send-interval = send-interval-in-seconds

@cindex dns-send-interval
The minimum send interval (= maximum rate) that the DNS transport will use to send new DNS requests. GVPE will not exceed this rate even when the latency is very low. The default is @t{0.01}, which means GVPE will not send more than 100 DNS requests per connection per second. For high-bandwidth links you could go lower, e.g. to @t{0.001} or so. For congested or rate-limited links, you might want to go higher, say @t{0.1}, @t{0.2} or even higher.
@refill
The default should be working OK for most links.
@refill


@item
dns-timeout-factor = float

@cindex dns-timeout-factor
Factor to multiply the @t{min_latency} (see @t{dns-overlap-factor}) by to get request timeouts. The default of @t{8} means that the DNS transport will resend the request when no reply has been received for longer than eight times the minimum (= expected) latency, assuming the request or reply has been lost.
@refill
For congested links a higher value might be necessary (e.g. @t{30}). If the link is very stable lower values (e.g. @t{2}) might work nicely. Values near or below @t{1} makes no sense whatsoever.
@refill
The default should be working OK for most links but will result in low throughput if packet loss is high.
@refill


@item
if-up = relative-or-absolute-path

@cindex if-up
Sets the path of a script that should be called immediately after the network interface is initialized (but not necessarily up). The following environment variables are passed to it (the values are just examples).
@refill
Variables that have the same value on all nodes:
@refill


@itemize


@item
CONFBASE=/etc/gvpe

@cindex CONFBASE
The configuration base directory.
@refill


@item
IFNAME=vpn0

@cindex IFNAME
The network interface to initialize.
@refill


@item
IFTYPE=native # or tincd

@cindex IFTYPE


@item
IFSUBTYPE=linux # or freebsd, darwin etc..

@cindex IFSUBTYPE
The interface type (@t{native} or @t{tincd}) and the subtype (usually the OS name in lowercase) that this GVPE was configured for. Can be used to select the correct syntax to use for network-related commands.
@refill


@item
MTU=1436

@cindex MTU
The MTU to set the interface to. You can use lower values (if done consistently on all nodes), but this is usually either inefficient or simply ineffective.
@refill


@item
NODES=5

@cindex NODES
The number of nodes in this GVPE network.
@refill
@end itemize

Variables that are node-specific and with values pertaining to the node running this GVPE:
@refill


@itemize


@item
IFUPDATA=string

@cindex IFUPDATA
The value of the configuration directive @t{if-up-data}.
@refill


@item
MAC=fe:fd:80:00:00:01

@cindex MAC
The MAC address the network interface has to use.
@refill
Might be used to initialize interfaces on platforms where GVPE does not do this automatically.  Please see the @t{gvpe.osdep(5)} man page for platform-specific information.
@refill


@item
NODENAME=branch1

@cindex NODENAME
The nickname of the node.
@refill


@item
NODEID=1

@cindex NODEID
The numerical node ID of the node running this instance of GVPE. The first node mentioned in the config file gets ID 1, the second ID 2 and so on.
@refill
@end itemize

In addition, all node-specific variables (except @t{NODEID}) will be available with a postfix of @t{_nodeid}, which contains the value for that node, e.g. the @t{MAC_1} variable contains the MAC address of node #1, while the @t{NODENAME_22} variable contains the name of node #22.
@refill
Here is a simple if-up script:
@refill


@example
   #!/bin/sh
   ip link set $IFNAME up
   [ $NODENAME = branch1 ] && ip addr add 10.0.0.1 dev $IFNAME
   [ $NODENAME = branch2 ] && ip addr add 10.1.0.1 dev $IFNAME
   ip route add 10.0.0.0/8 dev $IFNAME
@end example

More complicated examples (using routing to reduce ARP traffic) can be found in the @file{etc/} subdirectory of the distribution.
@refill


@item
ifname = devname

@cindex ifname
Sets the tun interface name to the given name. The default is OS-specific and most probably something like @t{tun0}.
@refill


@item
ifpersist = yes|true|on | no|false|off

@cindex ifpersist
Should the tun/tap device be made persistent, that is, should the device stay up even when gvpe exits? Some versions of the tunnel device have problems sending packets when gvpe is restarted in persistent mode, so if the connections can be established but you cannot send packets from the local node, try to set this to @t{off} and do an ifconfig down on the device.
@refill


@item
ip-proto = numerical-ip-protocol

@cindex ip-proto
Sets the protocol number to be used for the rawip protocol. This is a global option because all nodes must use the same protocol, and since there are no port numbers, you cannot easily run more than one gvpe instance using the same protocol, nor can you share the protocol with other programs.
@refill
The default is 47 (GRE), which has a good chance of tunneling through firewalls (but note that gvpe's rawip protocol is not GRE compatible). Other common choices are 50 (IPSEC, ESP), 51 (IPSEC, AH), 4 (IPIP tunnels) or 98 (ENCAP, rfc1241).
@refill
Many versions of Linux seem to have a bug that causes them to reorder packets for some ip protocols (GRE, ESP) but not for others (AH), so choose wisely (that is, use 51, AH).
@refill


@item
http-proxy-host = hostname/ip

@cindex http-proxy-host
The @t{http-proxy-*} family of options are only available if gvpe was compiled with the @t{--enable-http-proxy} option and enable tunneling of tcp connections through a http proxy server.
@refill
@t{http-proxy-host} and @t{http-proxy-port} should specify the hostname and port number of the proxy server. See @t{http-proxy-loginpw} if your proxy requires authentication.
@refill
Please note that gvpe will still try to resolve all hostnames in the configuration file, so if you are behind a proxy without access to a DNS server better use numerical IP addresses.
@refill
To make best use of this option disable all protocols except TCP in your config file and make sure your routers (or all other nodes) are listening on a port that the proxy allows (443, https, is a common choice).
@refill
If you have a router, connecting to it will suffice. Otherwise TCP must be enabled on all nodes.
@refill
Example:
@refill


@example
   http-proxy-host = proxy.example.com
   http-proxy-port = 3128       # 8080 is another common choice
   http-proxy-auth = schmorp:grumbeere
@end example


@item
http-proxy-port = proxy-tcp-port

@cindex http-proxy-port
The port where your proxy server listens.
@refill


@item
http-proxy-auth = login:password

@cindex http-proxy-auth
The optional login and password used to authenticate to the proxy server, separated by a literal colon (@t{:}). Only basic authentication is currently supported.
@refill


@item
keepalive = seconds

@cindex keepalive
Sets the keepalive probe interval in seconds (default: @t{60}). After this many seconds of inactivity the daemon will start to send keepalive probe every 3 seconds until it receives a reply from the other end.  If no reply is received within 15 seconds, the peer is considered unreachable and the connection is closed.
@refill


@item
loglevel = noise|trace|debug|info|notice|warn|error|critical

@cindex loglevel
Set the logging level. Connection established messages are logged at level @t{info}, notable errors are logged with @t{error}. Default is @t{info}.
@refill


@item
mtu = bytes

@cindex mtu
Sets the maximum MTU that should be used on outgoing packets (basically the MTU of the outgoing interface) The daemon will automatically calculate maximum overhead (e.g. UDP header size, encryption blocksize...) and pass this information to the @t{if-up} script.
@refill
Recommended values are 1500 (ethernet), 1492 (pppoe), 1472 (pptp).
@refill
This value must be the minimum of the MTU values of all nodes.
@refill


@item
node = nickname

@cindex node
Not really a config setting but introduces a node section. The nickname is used to select the right configuration section and must be passed as an argument to the gvpe daemon.
@refill


@item
node-up = relative-or-absolute-path

@cindex node-up
Sets a command (default: none) that should be called whenever a connection is established (even on rekeying operations). Note that node-up/down scripts will be run asynchronously, but execution is serialised, so there will only ever be one such script running.
@refill
In addition to all the variables passed to @t{if-up} scripts, the following environment variables will be set (values are just examples):
@refill


@itemize


@item
DESTNODE=branch2

@cindex DESTNODE
The name of the remote node.
@refill


@item
DESTID=2

@cindex DESTID
The node id of the remote node.
@refill


@item
DESTSI=rawip/88.99.77.55:0

@cindex DESTSI
The "socket info" of the target node, protocol dependent but usually in the format protocol/ip:port.
@refill


@item
DESTIP=188.13.66.8

@cindex DESTIP
The numerical IP address of the remote node (gvpe accepts connections from everywhere, as long as the other node can authenticate itself).
@refill


@item
DESTPORT=655 # deprecated

@cindex DESTPORT
The protocol port used by the other side, if applicable.
@refill


@item
STATE=up

@cindex STATE
Node-up scripts get called with STATE=up, node-change scripts get called with STATE=change and node-down scripts get called with STATE=down.
@refill
@end itemize

Here is a nontrivial example that uses nsupdate to update the name => ip mapping in some DNS zone:
@refill


@example
   #!/bin/sh
   @{
     echo update delete $DESTNODE.lowttl.example.net. a
     echo update add $DESTNODE.lowttl.example.net. 1 in a $DESTIP
     echo   
   @} | nsupdate -d -k $CONFBASE:key.example.net.
@end example


@item
node-change = relative-or-absolute-path

@cindex node-change
Same as @t{node-change}, but gets called whenever something about a connection changes (such as the source IP address).
@refill


@item
node-down = relative-or-absolute-path

@cindex node-down
Same as @t{node-up}, but gets called whenever a connection is lost.
@refill


@item
pid-file = path

@cindex pid-file
The path to the pid file to check and create (default: @t{LOCALSTATEDIR/run/gvpe.pid}).
@refill


@item
private-key = relative-path-to-key

@cindex private-key
Sets the path (relative to the config directory) to the private key (default: @t{hostkey}). This is a printf format string so every @t{%} must be doubled. A single @t{%s} is replaced by the hostname, so you could use paths like @t{hostkeys/%s} to fetch the files at the location where @t{gvpectrl} puts them.
@refill
Since only the private key file of the current node is used and the private key file should be kept secret per-node to avoid spoofing, it is not recommended to use this feature.
@refill


@item
rekey = seconds

@cindex rekey
Sets the rekeying interval in seconds (default: @t{3600}). Connections are reestablished every @t{rekey} seconds, making them use a new encryption key.
@refill


@item
nfmark = integer

@cindex nfmark
This advanced option, when set to a nonzero value (default: @t{0}), tries to set the netfilter mark (or fwmark) value on all sockets gvpe uses to send packets.
@refill
This can be used to make gvpe use a different set of routing rules. For example, on GNU/Linux, the @t{if-up} could set @t{nfmark} to 1000 and then put all routing rules into table @t{99} and then use an ip rule to make gvpe traffic avoid that routing table, in effect routing normal traffic via gvpe and gvpe traffic via the normal system routing tables:
@refill


@example
   ip rule add not fwmark 1000 lookup 99
@end example

@end itemize


@subsection NODE SPECIFIC SETTINGS
The following settings are node-specific, that is, every node can have different settings, even within the same gvpe instance. Settings that are set before the first node section set the defaults, settings that are set within a node section only apply to the given node.
@refill


@itemize


@item
allow-direct = nodename

@cindex allow-direct
Allow direct connections to this node. See @t{deny-direct} for more info.
@refill


@item
compress = yes|true|on | no|false|off

@cindex compress
For the current node, this specified whether it will accept compressed packets, and for all other nodes, this specifies whether to try to compress data packets sent to this node (default: @t{yes}). Compression is really cheap even on slow computers, has no size overhead at all and will only be used when the other side supports compression, so enabling this is often a good idea.
@refill


@item
connect = ondemand | never | always | disabled

@cindex connect
Sets the connect mode (default: @t{always}). It can be @t{always} (always try to establish and keep a connection to the given node), @t{never} (never initiate a connection to the given host, but accept connections), @t{ondemand} (try to establish a connection when there are outstanding packets in the queue and take it down after the keepalive interval) or @t{disabled} (node is bad, don't talk to it).
@refill
Routers will automatically be forced to @t{always} unless they are @t{disabled}, to ensure all nodes can talk to each other.
@refill


@item
deny-direct = nodename | *

@cindex deny-direct
Deny direct connections to the specified node (or all nodes when @t{*} is given). Only one node can be specified, but you can use multiple @t{allow-direct} and @t{deny-direct} statements. This only makes sense in networks with routers, as routers are required for indirect connections.
@refill
Sometimes, a node cannot reach some other nodes for reasons of network connectivity. For example, a node behind a firewall that only allows connections to/from a single other node in the network. In this case one should specify @t{deny-direct = *} and @t{allow-direct = othernodename} (the other node @emph{must} be a router for this to work).
@refill
The algorithm to check whether a connection may be direct is as follows:
@refill
1. Other node mentioned in an @t{allow-direct}? If yes, allow the connection.
@refill
2. Other node mentioned in a @t{deny-direct}? If yes, deny direct connections.
@refill
3. Allow the connection.
@refill
That is, @t{allow-direct} takes precedence over @t{deny-direct}.
@refill
The check is done in both directions, i.e. both nodes must allow a direct connection before one is attempted, so you only need to specify connect limitations on one node.
@refill


@item
dns-domain = domain-suffix

@cindex dns-domain
The DNS domain suffix that points to the DNS tunnel server for this node.
@refill
The domain must point to a NS record that points to the @emph{dns-hostname}, i.e.
@refill


@example
   dns-domainname = tunnel.example.net
   dns-hostname   = tunnel-server.example.net
@end example

Corresponds to the following DNS entries in the @t{example.net} domain:
@refill


@example
   tunnel.example.net.         NS tunnel-server.example.net.
   tunnel-server.example.net.  A  13.13.13.13
@end example


@item
dns-hostname = hostname/ip

@cindex dns-hostname
The address to bind the DNS tunnel socket to, similar to the @t{hostname}, but for the DNS tunnel protocol only. Default: @t{0.0.0.0}, but that might change.
@refill


@item
dns-port = port-number

@cindex dns-port
The port to bind the DNS tunnel socket to. Must be @t{53} on DNS tunnel servers.
@refill


@item
enable-dns = yes|true|on | no|false|off

@cindex enable-dns
See gvpe.protocol(7) for a description of the DNS transport protocol. Avoid this protocol if you can.
@refill
Enable the DNS tunneling protocol on this node, either as server or as client. Support for this transport protocol is only available when gvpe was compiled using the @t{--enable-dns} option.
@refill


@item
enable-icmp = yes|true|on | no|false|off

@cindex enable-icmp
See gvpe.protocol(7) for a description of the ICMP transport protocol.
@refill
Enable the ICMP transport using ICMP packets of type @t{icmp-type} on this node.
@refill


@item
enable-rawip = yes|true|on | no|false|off

@cindex enable-rawip
See gvpe.protocol(7) for a description of the RAW IP transport protocol.
@refill
Enable the RAW IPv4 transport using the @t{ip-proto} protocol (default: @t{no}).
@refill


@item
enable-tcp = yes|true|on | no|false|off

@cindex enable-tcp
See gvpe.protocol(7) for a description of the TCP transport protocol.
@refill
Enable the TCPv4 transport using the @t{tcp-port} port (default: @t{no}). Support for this transport protocol is only available when gvpe was compiled using the @t{--enable-tcp} option.
@refill


@item
enable-udp = yes|true|on | no|false|off

@cindex enable-udp
See gvpe.protocol(7) for a description of the UDP transport protocol.
@refill
Enable the UDPv4 transport using the @t{udp-port} port (default: @t{no}, unless no other protocol is enabled for a node, in which case this protocol is enabled automatically).
@refill
NOTE: Please specify @t{enable-udp = yes} if you want to use it even though it might get switched on automatically, as some future version might default to another default protocol.
@refill


@item
hostname = hostname | ip    [can not be defaulted]

@cindex hostname
Forces the address of this node to be set to the given DNS hostname or IP address. It will be resolved before each connect request, so dyndns should work fine. If this setting is not specified and a router is available, then the router will be queried for the address of this node. Otherwise, the connection attempt will fail.
@refill
Note that DNS resolving is done synchronously, pausing the daemon. If that is an issue you need to specify IP addresses.
@refill


@item
icmp-type = integer

@cindex icmp-type
Sets the type value to be used for outgoing (and incoming) packets sent via the ICMP transport.
@refill
The default is @t{0} (which is @t{echo-reply}, also known as "ping-reply"). Other useful values include @t{8} (@t{echo-request}, a.k.a. "ping") and @t{11} (@t{time-exceeded}), but any 8-bit value can be used.
@refill


@item
if-up-data = value

@cindex if-up-data
The value specified using this directive will be passed to the @t{if-up} script in the environment variable @t{IFUPDATA}.
@refill


@item
inherit-tos = yes|true|on | no|false|off

@cindex inherit-tos
Whether to inherit the TOS settings of packets sent to the tunnel when sending packets to this node (default: @t{yes}). If set to @t{yes} then outgoing tunnel packets will have the same TOS setting as the packets sent to the tunnel device, which is usually what you want.
@refill


@item
max-retry = positive-number

@cindex max-retry
The maximum interval in seconds (default: @t{3600}, one hour) between retries to establish a connection to this node. When a connection cannot be established, gvpe uses exponential back-off capped at this value. It's sometimes useful to set this to a much lower value (e.g. @t{120}) on connections to routers that usually are stable but sometimes are down, to assure quick reconnections even after longer downtimes.
@refill


@item
max-ttl = seconds

@cindex max-ttl
Expire packets that couldn't be sent after this many seconds (default: @t{60}). Gvpe will normally queue packets for a node without an active connection, in the hope of establishing a connection soon. This value specifies the maximum lifetime a packet will stay in the queue, if a packet gets older, it will be thrown away.
@refill


@item
max-queue = positive-number>=1

@cindex max-queue
The maximum number of packets that will be queued (default: @t{512}) for this node. If more packets are sent then earlier packets will be expired. See @t{max-ttl}, above.
@refill


@item
router-priority = 0 | 1 | positive-number>=2

@cindex router-priority
Sets the router priority of the given node (default: @t{0}, disabled).
@refill
If some node tries to connect to another node but it doesn't have a hostname, it asks a router node for it's IP address. The router node chosen is the one with the highest priority larger than @t{1} that is currently reachable. This is called a @emph{mediated} connection, as the connection itself will still be direct, but it uses another node to mediate between the two nodes.
@refill
The value @t{0} disables routing, that means if the node receives a packet not for itself it will not forward it but instead drop it.
@refill
The special value @t{1} allows other hosts to route through the router host, but they will never route through it by default (i.e. the config file of another node needs to specify a router priority higher than one to choose such a node for routing).
@refill
The idea behind this is that some hosts can, if required, bump the @t{router-priority} setting to higher than @t{1} in their local config to route through specific hosts. If @t{router-priority} is @t{0}, then routing will be refused, so @t{1} serves as a "enable, but do not use by default" switch.
@refill
Nodes with @t{router-priority} set to @t{2} or higher will always be forced to @t{connect} = @t{always} (unless they are @t{disabled}).
@refill


@item
tcp-port = port-number

@cindex tcp-port
Similar to @t{udp-port} (default: @t{655}), but sets the TCP port number.
@refill


@item
udp-port = port-number

@cindex udp-port
Sets the port number used by the UDP protocol (default: @t{655}, not officially assigned by IANA!).
@refill
@end itemize


@section CONFIG DIRECTORY LAYOUT
The default (or recommended) directory layout for the config directory is:
@refill


@itemize


@item
gvpe.conf

The config file.
@refill


@item
if-up

The if-up script
@refill


@item
node-up, node-down

If used the node up or node-down scripts.
@refill


@item
hostkey

The private key (taken from @t{hostkeys/nodename}) of the current host.
@refill


@item
pubkey/nodename

The public keys of the other nodes, one file per node.
@refill
@end itemize


@node gvpectrl,gvpe,gvpe.conf,Top

@chapter gvpectrl

@section NAME
@t{gvpectrl} - GNU Virtual Private Ethernet Control Program
@refill


@section SYNOPSIS
@t{gvpectrl} [@strong{-ckgs}] [@strong{--config=}@emph{DIR}] [@strong{--generate-keys}] [@strong{--help}] [@strong{--kill}[@strong{=}@emph{SIGNAL}]] [@strong{--show-config}] [@strong{--version}]
@refill


@section DESCRIPTION
This is the control program for the @t{gvpe}, the virtual private ethernet daemon.
@refill


@section OPTIONS


@itemize


@item
@strong{-c}, @strong{--config=}@emph{DIR}

Read configuration options from @emph{DIR}.
@refill


@item
@strong{-g}, @strong{--generate-keys}

Generate public/private RSA key-pair and exit.
@refill


@item
@strong{-q}, @strong{--quiet}

Suppresses messages the author finds nonessential for scripting purposes.
@refill


@item
@strong{--help}

Display short list of options.
@refill


@item
@strong{--kill}[@strong{=}@emph{SIGNAL}]

Attempt to kill a running @t{gvpectrl} (optionally with the specified @emph{SIGNAL} instead of @t{SIGTERM}) and exit.
@refill


@item
@strong{--show-config}

Show a summary of the configuration, and how gvpe interprets it. Can also be very useful when designing firewall scripts.
@refill


@item
@strong{--version}

Output version information and exit.
@refill
@end itemize


@section BUGS
If you find any bugs, report them to @t{gvpe@@schmorp.de}.
@refill


@node gvpe,gvpe.protocol,gvpectrl,Top

@chapter gvpe

@section NAME
@t{gvpe} - GNU Virtual Private Ethernet Daemon
@refill


@section SYNOPSIS
@t{gvpe} [@strong{-cDlL}] [@strong{--config=}@emph{DIR}] [@strong{--no-detach}] [@strong{-l=}@emph{LEVEL]}] [@strong{--kill}[@strong{=}@emph{SIGNAL}]] [@strong{--mlock}] [@strong{--help}] [@strong{--version}] @emph{NODENAME} [@emph{option...}]
@refill


@section DESCRIPTION
See the gvpe(5) man page for an introduction to the gvpe suite.
@refill
This is the manual page for gvpe, the virtual private ethernet daemon. When started, @t{gvpe} will read it's configuration file to determine the network topology, and other configuration information, assuming the role of node @emph{NODENAME}
@refill
It will then create/connect to the tun/tap device and set up a socket for incoming connections. Then a @t{if-up} script will be executed to further configure the virtual network device. If that succeeds, it will detach from the controlling terminal and continue in the background, accepting and setting up connections to other gvpe daemons that are part of the same virtual private ethernet.
@refill
The optional arguments after the node name have to be of the form:
@refill


@example
   [I<nodename>.]var=value
@end example

If the argument has a prefix of @t{nodename.} (i.e. @t{laptop.enable-dns=yes}) then it will be parsed after all the config directives for that node, if not, it is parsed before the first node directive in the config file, and can be used to set global options or default variables.
@refill
For example, to start @t{gvpe} in the foreground, with log-level @t{info} on the node @t{laptop}, with TCP enabled and HTTP-Proxy host and Port set, use this:
@refill


@example
  gvpe -D -l info laptop \
       http-proxy-host=10.0.0.18 http-proxy-port=3128 \
       laptop.enable-tcp=yes
@end example


@section OPTIONS


@itemize


@item
@strong{-c}, @strong{--config=}@emph{DIR}

Read configuration options from @emph{DIR}
@refill


@item
@strong{-d}, @strong{--l=}@emph{LEVEL}

Set logging level to @emph{LEVEL} (one of: noise, trace, debug, info, notice, warn, error, critical).
@refill


@item
@strong{--help}

Display short list of options.
@refill


@item
@strong{-D}, @strong{--no-detach}

Don't fork and detach but stay in foreground and log messages to stderr in addition to syslog.
@refill


@item
@strong{-L}, @strong{--mlock}

Lock @t{gvpe} into main memory. This will prevent sensitive data like shared private keys to be written to the system swap files/partitions.
@refill


@item
@strong{--version}

Output version information and exit.
@refill
@end itemize


@section SIGNALS


@itemize


@item
HUP

Closes/resets all connections, resets the retry time and will start connecting again (it will NOT re-read the config file). This is useful e.g. in a @t{/etc/ppp/if-up} script.
@refill


@item
TERM

Closes/resets all connections and exits.
@refill


@item
USR1

Dump current network status into the syslog (at loglevel @t{notice}, so make sure your loglevel allows this).
@refill
@end itemize


@section FILES


@itemize


@item
@t{/etc/gvpe/gvpe.conf}

The configuration file for @t{gvpe}.
@refill


@item
@t{/etc/gvpe/if-up}

Script which is executed as soon as the virtual network device has been allocated.  Purpose is to further configure that device.
@refill


@item
@t{/etc/gvpe/node-up}

Script which is executed whenever a node connects to this node. This can be used for example to run nsupdate.
@refill


@item
@t{/etc/gvpe/node-down}

Script which is executed whenever a connection to another node is lost. for example to run nsupdate.
@refill


@item
@t{/etc/gvpe/pubkey/*}

The directory containing the public keys for every node, usually autogenerated by executing @t{gvpectrl --generate-keys}.
@refill


@item
@t{/var/run/gvpe.pid}

The PID of the currently running @t{gvpe} is stored in this file.
@refill
@end itemize


@section BUGS
The cryptography in gvpe has not been thoroughly checked by many people yet. Use it at your own risk!
@refill
If you find any bugs, report them to @t{gvpe@@schmorp.de}.
@refill


@node gvpe.protocol,Simple Example,gvpe,Top

@chapter gvpe.protocol

@section The GNU-VPE Protocols


@section Overview
GVPE can make use of a number of protocols. One of them is the GNU VPE protocol which is used to authenticate tunnels and send encrypted data packets. This protocol is described in more detail the second part of this document.
@refill
The first part of this document describes the transport protocols which are used by GVPE to send it's data packets over the network.
@refill


@section PART 1: Transport protocols
GVPE offers a wide range of transport protocols that can be used to interchange data between nodes. Protocols differ in their overhead, speed, reliability, and robustness.
@refill
The following sections describe each transport protocol in more detail. They are sorted by overhead/efficiency, the most efficient transport is listed first:
@refill


@subsection RAW IP
This protocol is the best choice, performance-wise, as the minimum overhead per packet is only 38 bytes.
@refill
It works by sending the VPN payload using raw IP frames (using the protocol set by @t{ip-proto}).
@refill
Using raw IP frames has the drawback that many firewalls block "unknown" protocols, so this transport only works if you have full IP connectivity between nodes.
@refill


@subsection ICMP
This protocol offers very low overhead (minimum 42 bytes), and can sometimes tunnel through firewalls when other protocols can not.
@refill
It works by prepending an ICMP header with type @t{icmp-type} and a code of @t{255}. The default @t{icmp-type} is @t{echo-reply}, so the resulting packets look like echo replies, which looks rather strange to network administrators.
@refill
This transport should only be used if other transports (i.e. raw IP) are not available or undesirable (due to their overhead).
@refill


@subsection UDP
This is a good general choice for the transport protocol as UDP packets tunnel well through most firewalls and routers, and the overhead per packet is moderate (minimum 58 bytes).
@refill
It should be used if RAW IP is not available.
@refill


@subsection TCP
This protocol is a very bad choice, as it not only has high overhead (more than 60 bytes), but the transport also retries on it's own, which leads to congestion when the link has moderate packet loss (as both the TCP transport and the tunneled traffic will retry, increasing congestion more and more). It also has high latency and is quite inefficient.
@refill
It's only useful when tunneling through firewalls that block better protocols. If a node doesn't have direct internet access but a HTTP proxy that supports the CONNECT method it can be used to tunnel through a web proxy. For this to work, the @t{tcp-port} should be @t{443} (@t{https}), as most proxies do not allow connections to other ports.
@refill
It is an abuse of the usage a proxy was designed for, so make sure you are allowed to use it for GVPE.
@refill
This protocol also has server and client sides. If the @t{tcp-port} is set to zero, other nodes cannot connect to this node directly. If the @t{tcp-port} is non-zero, the node can act both as a client as well as a server.
@refill


@subsection DNS
@strong{WARNING:} Parsing and generating DNS packets is rather tricky. The code almost certainly contains buffer overflows and other, likely exploitable, bugs. You have been warned.
@refill
This is the worst choice of transport protocol with respect to overhead (overhead can be 2-3 times higher than the transferred data), and latency (which can be many seconds). Some DNS servers might not be prepared to handle the traffic and drop or corrupt packets. The client also has to constantly poll the server for data, so the client will constantly create traffic even if it doesn't need to transport packets.
@refill
In addition, the same problems as the TCP transport also plague this protocol.
@refill
It's only use is to tunnel through firewalls that do not allow direct internet access. Similar to using a HTTP proxy (as the TCP transport does), it uses a local DNS server/forwarder (given by the @t{dns-forw-host} configuration value) as a proxy to send and receive data as a client, and an @t{NS} record pointing to the GVPE server (as given by the @t{dns-hostname} directive).
@refill
The only good side of this protocol is that it can tunnel through most firewalls mostly undetected, iff the local DNS server/forwarder is sane (which is true for most routers, wireless LAN gateways and nameservers).
@refill
Fine-tuning needs to be done by editing @t{src/vpn_dns.C} directly.
@refill


@section PART 2: The GNU VPE protocol
This section, unfortunately, is not yet finished, although the protocol is stable (until bugs in the cryptography are found, which will likely completely change the following description). Nevertheless, it should give you some overview over the protocol.
@refill


@subsection Anatomy of a VPN packet
The exact layout and field lengths of a VPN packet is determined at compile time and doesn't change. The same structure is used for all transport protocols, be it RAWIP or TCP.
@refill


@example
 +------+------+--------+------+
 | HMAC | TYPE | SRCDST | DATA |
 +------+------+--------+------+
@end example

The HMAC field is present in all packets, even if not used (e.g. in auth request packets), in which case it is set to all zeroes. The checksum itself is calculated over the TYPE, SRCDST and DATA fields in all cases.
@refill
The TYPE field is a single byte and determines the purpose of the packet (e.g. RESET, COMPRESSED/UNCOMPRESSED DATA, PING, AUTH REQUEST/RESPONSE, CONNECT REQUEST/INFO etc.).
@refill
SRCDST is a three byte field which contains the source and destination node IDs (12 bits each).
@refill
The DATA portion differs between each packet type, naturally, and is the only part that can be encrypted. Data packets contain more fields, as shown:
@refill


@example
 +------+------+--------+------+-------+------+
 | HMAC | TYPE | SRCDST | RAND | SEQNO | DATA |
 +------+------+--------+------+-------+------+
@end example

RAND is a sequence of fully random bytes, used to increase the entropy of the data for encryption purposes.
@refill
SEQNO is a 32-bit sequence number. It is negotiated at every connection initialization and starts at some random 31 bit value. VPE currently uses a sliding window of 512 packets/sequence numbers to detect reordering, duplication and replay attacks.
@refill


@subsection The authentication protocol
Before nodes can exchange packets, they need to establish authenticity of the other side and a key. Every node has a private RSA key and the public RSA keys of all other nodes.
@refill
A host establishes a simplex connection by sending the other node an RSA encrypted challenge containing a random challenge (consisting of the encryption key to use when sending packets, more random data and PKCS1_OAEP padding) and a random 16 byte "challenge-id" (used to detect duplicate auth packets). The destination node will respond by replying with an (unencrypted) RIPEMD160 hash of the decrypted challenge, which will authenticate that node. The destination node will also set the outgoing encryption parameters as given in the packet.
@refill
When the source node receives a correct auth reply (by verifying the hash and the id, which will expire after 120 seconds), it will start to accept data packets from the destination node.
@refill
This means that a node can only initiate a simplex connection, telling the other side the key it has to use when it sends packets. The challenge reply is only used to set the current IP address of the other side and protocol parameters.
@refill
This protocol is completely symmetric, so to be able to send packets the destination node must send a challenge in the exact same way as already described (so, in essence, two simplex connections are created per node pair).
@refill


@subsection Retrying
When there is no response to an auth request, the node will send auth requests in bursts with an exponential back-off. After some time it will resort to PING packets, which are very small (8 bytes + protocol header) and lightweight (no RSA operations required). A node that receives ping requests from an unconnected peer will respond by trying to create a connection.
@refill
In addition to the exponential back-off, there is a global rate-limit on a per-IP base. It allows long bursts but will limit total packet rate to something like one control packet every ten seconds, to avoid accidental floods due to protocol problems (like a RSA key file mismatch between two nodes).
@refill
The intervals between retries are limited by the @t{max-retry} configuration value. A node with @t{connect} = @t{always} will always retry, a node with @t{connect} = @t{ondemand} will only try (and re-try) to connect as long as there are packets in the queue, usually this limits the retry period to @t{max-ttl} seconds.
@refill
Sending packets over the VPN will reset the retry intervals as well, which means as long as somebody is trying to send packets to a given node, GVPE will try to connect every few seconds.
@refill


@subsection Routing and Protocol translation
The GVPE routing algorithm is easy: there isn't much routing to speak of: When routing packets to another node, GVPE trues the following options, in order:
@refill


@itemize


@item
If the two nodes should be able to reach each other directly (common protocol, port known), then GVPE will send the packet directly to the other node.


@item
If this isn't possible (e.g. because the node doesn't have a @t{hostname} or known port), but the nodes speak a common protocol and a router is available, then GVPE will ask a router to "mediate" between both nodes (see below).


@item
If a direct connection isn't possible (no common protocols) or forbidden (@t{deny-direct}) and there are any routers, then GVPE will try to send packets to the router with the highest priority that is connected already @emph{and} is able (as specified by the config file) to connect directly to the target node.


@item
If no such router exists, then GVPE will simply send the packet to the node with the highest priority available.


@item
Failing all that, the packet will be dropped.

@end itemize

A host can usually declare itself unreachable directly by setting it's port number(s) to zero. It can declare other hosts as unreachable by using a config-file that disables all protocols for these other hosts. Another option is to disable all protocols on that host in the other config files.
@refill
If two hosts cannot connect to each other because their IP address(es) are not known (such as dial-up hosts), one side will send a @emph{mediated} connection request to a router (routers must be configured to act as routers!), which will send both the originating and the destination host a connection info request with protocol information and IP address of the other host (if known). Both hosts will then try to establish a direct connection to the other peer, which is usually possible even when both hosts are behind a NAT gateway.
@refill
Routing via other nodes works because the SRCDST field is not encrypted, so the router can just forward the packet to the destination host. Since each host uses it's own private key, the router will not be able to decrypt or encrypt packets, it will just act as a simple router and protocol translator.
@refill


@node Simple Example,Complex Example,gvpe.protocol,Top

@chapter Simple Example
In this example, gvpe is used to implement a simple, UDP-based ethernet on three hosts.
@refill
The config file (@t{gvpe.conf}) is the same on all hosts:
@refill


@example
   enable-udp = yes     # use UDP
   udp-port = 407       # use this UDP port
   mtu = 1492           # handy for TDSL
   ifname = vpn0        # I prefer vpn0 over e.g. tap0

   node = huffy         # arbitrary node name
   hostname = 1.2.3.4   # ip address if this host

   node = welshy
   hostname = www.example.net # resolve at connection time

   node = wheelery
   # no hostname, will be determinded dynamically using router1 or router2
@end example

@t{gvpe} will execute the @t{if-up} script on every hosts, which, for linux, could look like this for all three hosts:
@refill


@example
   ifconfig $IFNAME hw ether $MAC mtu $MTU
   ifconfig $IFNAME 10.0.0.$NODE
   route add -net 10.0.0.0 netmask 255.0.0.0 dev $IFNAME
@end example

The @t{10.0.0.$NODE} resolves to @t{10.0.0.1} on @t{huffy}, @t{10.0.0.2} on @t{welshy} and so on. Other schemes, such as @t{10.$NODE.0.1} might be useful, too.
@refill
After generating the keys (gvpectrl) and starting the daemon (@t{gvpe -D -l info }@emph{NODENAME} for test purposes) the three hosts should be able to ping each other.
@refill
If you have an internal @t{10.x.x.x} network (with a tighter netmask then @t{255.0.0.0}, e.g. @t{10.1.0.0} on @t{huffy}, @t{10.2.0.0} on @t{welshy} and so on), you can now enable ip-forwarding and proxy-arp (or set the hosts as default gateway), and your three hosts should forward traffic from each network to each other.
@refill


@node Complex Example,complex/gvpe.conf,Simple Example,Top

@chapter Complex Example
These files are configuration files for "our" internal network.

It is highly non-trivial, so don't use this configuration as the basis of
your network unless you know what you are doing.

It features: around 30 hosts, many of them have additional networks behind
them and use an assortment of different tunneling protocols. The vpn is
fully routed, no arp is used at all.

The public IP addresses of connecting nodes are automatically registered
via dns on the node ruth, using a node-up/node-down script.

And last not least: the if-up script can generate information to be used
in firewall rules (IP-net/MAC-address pairs) so ensure packet integrity so
you can use your iptables etc. firewall to filter by IP address only.

@menu
* complex/gvpe.conf:: An example gvpe configuration
* complex/if-up::     A fully-routing if-up config
* complex/node-up::   A node-up/node-down script utilizing dynds
@end menu


@node complex/gvpe.conf,complex/if-up,Complex Example,Complex Example

@chapter complex/gvpe.conf


@example
# sample configfile
# the config file must be exactly(!) the same on all nodes

rekey = 54321           # the rekeying interval
keepalive = 300         # the keepalive interval
on ruth keepalive = 120 # ruth is important and demands lower keepalives
on surfer keepalive = 40
mtu = 1492              # the mtu (minimum mtu of attached host)
ifname = vpn0           # the tunnel interface name to use
ifpersist = no          # the tun device should be persistent
inherit-tos = yes       # should tunnel packets inherit tos flags?
compress = yes          # wether compression should be used (NYI)
connect = ondemand      # connect to this host always/never or ondemand
router-priority = 1     # route for everybody - if necessary

loglevel = notice       # info logs connects, notice only important messages
on mobil loglevel = info
on doom loglevel = info
on ruth loglevel = info

udp-port = 407          # the udp port to use for sending/receiving packets
tcp-port = 443          # the tcp port to listen for connections (we use https over proxy)
ip-proto = 50           # (ab)use the ipsec protocol as rawip
icmp-type = 0           # (ab)use echo replies for tunneling
enable-udp = yes        # udp is spoken almost everywhere
enable-tcp = no         # tcp is not spoken everywhere
enable-rawip = no       # rawip is not spoken everywhere
enable-icmp = no        # most hosts don't bother to icmp

# every "node =" introduces a new node in the network
# the options following it don't set defaults but are
# node-specific.

# marc@@lap
node = mobil

# marc@@home
node = doom
enable-rawip = yes
enable-tcp = yes

# marc@@uni
node = ruth
enable-rawip = yes
enable-tcp = yes
enable-icmp = yes
hostname = 200.100.162.95
connect = always
router-priority = 30
on ruth node-up = node-up
on ruth node-down = node-up

# marc@@mu
node = frank
enable-rawip = yes
hostname = 44.88.167.250
router-priority = 20
connect = always

# nethype
node = rain
enable-rawip = yes
hostname = 145.253.105.130
router-priority = 10
connect = always

# marco@@home
node = marco
enable-rawip = yes

# stefan@@ka
node = wappla
connect = never

# stefan@@lap
node = stefan
udp-port = 408
connect = never

# paul@@wg
node = n8geil
on ruth enable-icmp = yes
on n8geil enable-icmp = yes
enable-udp = no

# paul@@lap
node = syrr

# paul@@lu
node = donomos

# marco@@hn
node = core

# elmex@@home
node = elmex
enable-rawip = yes
hostname = 100.251.143.181

# stefan@@kwc.at
node = fwkw
connect = never
on stefan connect = always
on wappla connect = always
hostname = 182.73.81.146

# elmex@@home
node = jungfrau
enable-rawip = yes

# uni main router
node = surfer
enable-rawip = yes
enable-tcp = no
enable-icmp = yes
hostname = 200.100.162.79
connect = always
router-priority = 40

# jkneer@@marvin
node = marvin
enable-rawip = yes
enable-udp = no

# jkneer@@entrophy
node = entrophy
enable-udp = no
enable-tcp = yes

# mr. primitive
node = voyager
enable-udp = no
enable-tcp = no
on voyager enable-tcp = yes
on voyager enable-udp = yes

# v-server (barbados.dn-systems.de)
#node = vserver
#enable-udp = yes
#hostname = 193.108.181.74
@end example


@node complex/if-up,complex/node-up,complex/gvpe.conf,Complex Example

@chapter complex/if-up


@example
#!/bin/bash

# Some environment variables will be set:
#
# CONFBASE=/etc/vpe     # the configuration directory prefix
# IFNAME=vpn0           # the network interface (ifname)
# MAC=fe:fd:80:00:00:01 # the mac-address to use for the interface
# NODENAME=cerebro      # the selected nodename (-n switch)
# NODEID=1              # the numerical node id
# MTU=1436              # the tunnel packet overhead (set mtu to 1500-$OVERHEAD)

# this if-up script is rather full-featured, and is used to
# generate a fully-routed (no arp traffic) vpn. the main portion
# consists of "ipn" calls (see below).

# some hosts require additional specific configuration, this is handled
# using if statements near the end of the script.

# with the --fw switch, outputs mac/net pairs for your firewall use:
# if-up --fw | while read mac net; do
#   iptables -t filter -A INPUT -i vpn0 -p all -m mac --mac-source \! $mac -s $net -j DROP
# done

ipn() @{
   local id="$1"; shift
   local mac=fe:fd:80:00:00:$(printf "%02x" $id)
   if [ -n "$FW" ]; then
      for net in "$@@"; do
         echo "$mac $net"
      done
   else
      local ip="$1"; shift
      if [ "$id" == $NODEID ]; then
         [ -n "$ADDR_ONLY" ] && ip addr add $ip broadcast 10.255.255.255 dev $IFNAME
      elif [ -z "$ADDR_ONLY" ]; then
         ip neighbour add $ip lladdr $mac nud permanent dev $IFNAME
         for route in "$@@"; do
            ip route add $route via $ip dev vpn0
         done
      fi
   fi
@}

ipns() @{
   # this contains the generic routing information for the vpn
   # each call to ipn has the following parameters:
   # ipn <node-id> <gateway-ip> [<route> ...]
   # the second line (ipn 2) means:
   # the second node (doom in the config file) has the ip address 10.0.0.5,
   # which is the gateway for the 10.0/28 network and three additional ip
   # addresses
   
   ipn  1 10.0.0.20
   ipn  2 10.0.0.5  10.0.0.0/28 #200.100.162.92 200.100.162.93 100.99.218.222
   ipn  3 10.0.0.17
   ipn  4 10.0.0.18
   ipn  5 10.0.0.19 10.3.0.0/16
   ipn  6 10.0.0.21 10.0.2.0/26 #200.100.162.17
   ipn  7 10.0.0.22 10.1.2.0/24 # wappla, off
   ipn  8 10.0.0.23 # stefan, off
   ipn  9 10.0.0.24 10.13.0.0/16
   ipn 10 10.0.0.25
   ipn 11 10.0.0.26
   ipn 12 10.0.0.27 10.0.2.64/26
   ipn 13 10.0.0.28 10.0.3.0/24
   ipn 14 10.0.0.29 10.1.1.0/24 # fwkw, off
   # mind the gateway ip gap
   ipn 15 10.9.0.30 10.0.4.0/24
   ipn 16 10.9.0.31
   ipn 17 10.9.0.32 10.42.0.0/16
   ipn 18 10.9.0.33
   ipn 19 10.9.0.34
   #ipn 20 10.9.0.35
@}

if [ "$1" == "--fw" ]; then
   FW=1

   ipns
else
   exec >/var/log/vpe.if-up 2>&1
   set -x

   [ $NODENAME = "ruth"    ] && ip link set $IFNAME down # hack

   # first set the link up and initialize the interface ip
   # address.
   ip link set $IFNAME address $MAC
   ip link set $IFNAME mtu $MTU up
   ADDR_ONLY=1 ipns # set addr only

   # now initialize the main vpn routes (10.0/8)
   # the second route is a hack to to reach some funnily-connected
   # machines.
   ip route add 10.0.0.0/8 dev $IFNAME
   ip route add 10.0.0.0/27 dev $IFNAME

   ipns # set the interface routes

   # now for something completely different, ehr, something not
   # easily doable with ipn, namely some extra specific highly complicated
   # and non-regular setups for some machines.
   if [ $NODENAME = doom ]; then
      ip addr add 200.100.162.92 dev $IFNAME
      ip route add 200.100.0.0/16 via 10.0.0.17 dev $IFNAME
      ip route flush table 101
      ip route add table 101 default src 200.100.162.92 via 10.0.0.17 dev $IFNAME

      ip addr add 100.99.218.222 dev $IFNAME
      ip route add 100.99.218.192/27 via 10.0.0.19 dev $IFNAME
      ip route flush table 103
      ip route add table 103 default src 100.99.218.222 via 10.0.0.19

   elif [ $NODENAME = marco ]; then
      ip addr add 200.100.162.17 dev $IFNAME

      for addr in 79 89 90 91 92 93 94 95; do
         ip route add 200.100.162.$addr dev ppp0
      done
      ip route add 200.100.76.0/23 dev ppp0
      ip route add src 200.100.162.17 200.100.0.0/16 via 10.0.0.17 dev $IFNAME

   elif [ $NODENAME = ruth ]; then
      ip route add 200.100.162.17 via 10.0.0.21 dev vpn0
      ip route add 200.100.162.92 via 10.0.0.5 dev vpn0
      ip route add 200.100.162.93 via 10.0.0.5 dev vpn0

   fi

   # and this is the second part of the 10.0/27 hack. don't ask.
   [ $NODENAME != fwkw ] && ip route add 10.0.0.0/24 via 10.0.0.29 dev $IFNAME
fi
@end example


@node complex/node-up,Index,complex/if-up,Complex Example

@chapter complex/node-up


@example
#!/bin/sh

# Some environment variables will be set (in addition the ones
# set in if-up, too):
#
# DESTNODE=doom         # others nodename
# DESTID=5              # others node id
# DESTIP=188.13.66.8    # others ip
# DESTPORT=407          # others port
# STATE=up/down         # node-up gets UP, node-down script gets DOWN

if [ $STATE = up ]; then
   @{
     echo update delete $DESTNODE.lowttl.example.com. a
     echo update delete $DESTNODE-last.lowttl.example.com. a
     echo update add $DESTNODE.lowttl.example.com. 1 in a $DESTIP
     echo update add $DESTNODE-last.lowttl.example.com. 1 in a $DESTIP
     echo
   @} | nsupdate -d -k $CONFBASE:marc.example.net.
else
   @{
     echo update delete $DESTNODE.lowttl.example.com. a
     echo update delete $DESTNODE-last.lowttl.example.com. a
     echo update add $DESTNODE-last.lowttl.example.com. 1 in a $DESTIP
     echo
   @} | nsupdate -d -k $CONFBASE:marc.example.net.
fi
@end example


@node Index,,complex/node-up,Top

@chapter Index
@printindex cp


@bye

Revision:	1.5
Committed:	Tue Feb 15 13:31:22 2011 UTC (13 years, 3 months ago) by root
Content type:	application/x-texinfo
Branch:	MAIN
CVS Tags:	rel-2_25
Changes since 1.4:	+132 -138 lines
Log Message:	* empty log message *