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gvpe

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Источник: http://cvs.savannah.gnu.org/viewvc/gvpe/README?revision=1.8&root=gvpe&view=markup


Содержание

[править] NAME

   GNU-VPE - Overview of the GNU Virtual Private Ethernet suite.


[править] 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.


[править] WHAT IS A VPN?

   VPN is an acronym, it stands for:
       Virtual means that no physical network is created (of course), but a
       network is *emulated* by creating multiple tunnels between the
       member nodes by encapsulating and sending data over another
       transport network.
       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.
       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.
       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.
       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.
       GVPE provides a true multi-point network in wich any number of nodes
       (at least a few dozen in practise, the theoretical limit is 4095
       nodes) can participate.


[править] GVPE DESIGN GOALS

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.
EASY TO SETUP
       A few lines of config (the config file is shared unmodified between
       all hosts) and a single run of ``gvpectrl to generate the keys
       suffices to make it work.
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.


[править] PROGRAMS

   Vpe comes with two programs: one daemon (``gvpe) and one control
   program (``gvpectrl).
gvpectrl
       Is used to generate the keys, check and give an overview of of the
       configuration and contorl the daemon (restarting etc.).
gvpe
       Is the daemon used to establish and maintain connections to the
       other network members. It should be run on the gateway machine.


[править] COMPILETIME CONFIGURATION

   Please have a look at the ``gvpe.osdep(5) manpage for
   platform-specific information.
   Here are a few recipes for compiling your gvpe, showing the extremes
   (fast, small, insecure OR slow, large, more secure), between you should
   choose:


[править] AS LOW PACKET OVERHEAD AS POSSIBLE

      ./configure --enable-hmac-length=4 --enable-rand-length=0
   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 easy, though.


[править] MINIMIZE CPU TIME REQUIRED

      ./configure --enable-cipher=bf --enable-digest=md4
   Use the fastest cipher and digest algorithms currently available in
   gvpe. MD4 has been broken and is quite insecure, though.


[править] MAXIMIZE SECURITY

      ./configure --enable-hmac-length=16 --enable-rand-length=8 --enable-digest=sha1
   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-224 and beyond, but support in openssl is missing as of writing this
   document.
   In general, remember that AES-128 seems to be more secure and 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 or
   RIPEMD160 are better, and Blowfish is a fast cipher (and also quite
   secure).


[править] 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.


[править] STEP 1: configuration

   First you have to create a daemon configuation file and put it into the
   configuration directory. This is usually ``/etc/gvpe, depending on how
   you configured gvpe, and can be overwritten using the ``-c commandline
   switch.
   Put the following lines into ``/etc/gvpe/gvpe.conf:
      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
   The only other file neccessary if the ``if-up script that initializes
   the local ethernet interface. Put the following lines into
   ``/etc/gvpe/if-up and make it execute (``chmod 755 /etc/gvpe/if-up):
      #!/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
   This script will give each node a different IP address in the
   ``10.0/16 network. The internal network (e.g. the ``eth0 interface)
   should then be set to a subset of that network, e.g. ``10.0.1.0/24 on
   node ``first, ``10.0.2.0/24 on node ``second, and so on.
   By enabling routing on the gateway host that runs ``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 even real briding), or
   (best) full routing - the choice is yours.


[править] STEP 2: create the RSA key pairs for all hosts

   Run the following command to generate all key pairs (that might take a
   while):
      gvpectrl -c /etc/gvpe -g
   This command will put the public keys into
   ``/etc/gvpe/pubkeys/*nodename* and the private keys into
   ``/etc/gvpe/hostkeys/*nodename*.


[править] STEP 3: distribute the config files to all nodes

   Now distribute the config files to the other nodes. This should be done
   in two steps, since the private keys should not be distributed. The
   example uses rsync-over-ssh
   First all the config files without the hostkeys should be distributed:
      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
   Then the hostkeys should be copied:
      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
   You should now check the configration by issuing the command ``gvpectrl
   -c /etc/gvpe -s on each node and verify it's output.


[править] STEP 4: starting gvpe

   You should then start gvpe on each node by issuing a command like:
      gvpe -D -linfo first # first is the nodename
   This will make the gvpe stay in foreground. You should then see
   "connection established" messages. If you don't see them check your
   firewall and routing (use tcpdump ;).
   If this works you should check your networking setup by pinging various
   endpoints.
   To make gvpe run more permanently you can either run it as a daemon (by
   starting it without the ``-D switch), or, much better, from your
   inittab. I use a line like this on my systems:
      t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1


[править] STEP 5: enjoy

   ... and play around. Sending a -HUP (``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, ``gvpectrl -k (or simply ``killall gvpe)
   will kill the daemon, start it again, making it read it's configuration
   files again.


[править] SEE ALSO

   gvpe.osdep(5) for OS-depedendent information, gvpe.conf(5), gvpectrl(8),
   and for a description of the transports, protocol, and routing
   algorithm, gvpe.protocol(7).
   The GVPE mailinglist, at <http://lists.schmorp.de/>, or
   ``gvpe@lists.schmorp.de.


[править] AUTHOR

   Marc Lehmann <gvpe@schmorp.de>


[править] COPYRIGHTS AND LICENSES

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


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