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2 | If you look for a more portable and/or featureful vpn implementation, look |
2 | ==== NAME ==== |
3 | at their tincd package: |
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4 | GNU-VPE - Overview of the GNU Virtual Private Ethernet suite. |
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6 | |
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7 | ==== DESCRIPTION ==== |
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9 | GVPE is a suite designed to provide a virtual private network for |
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10 | multiple nodes over an untrusted network. This document first gives an |
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11 | introduction to VPNs in general and then describes the specific |
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12 | implementation of GVPE. |
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14 | |
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15 | == WHAT IS A VPN? == |
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16 | |
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17 | VPN is an acronym, it stands for: |
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18 | |
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19 | : Virtual means that no physical network is created (of course), but a |
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20 | network is *emulated* by creating multiple tunnels between the |
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21 | member nodes by encapsulating and sending data over another |
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22 | transport network. |
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23 | |
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24 | Usually the emulated network is a normal IP or Ethernet, and the |
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25 | transport network is the Internet. However, using a VPN system like |
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26 | GVPE to connect nodes over other untrusted networks such as Wireless |
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27 | LAN is not uncommon. |
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28 | |
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29 | : Private means that non-participating nodes cannot decode ("sniff)" |
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30 | nor inject ("spoof") packets. This means that nodes can be connected |
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31 | over untrusted networks such as the public Internet without fear of |
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32 | being eavesdropped while at the same time being able to trust data |
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33 | sent by other nodes. |
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34 | |
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35 | In the case of GVPE, even participating nodes cannot sniff packets |
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36 | send to other nodes or spoof packets as if sent from other nodes, so |
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37 | communications between any two nodes is private to those two nodes. |
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38 | |
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39 | : Network means that more than two parties can participate in the |
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40 | network, so for instance it's possible to connect multiple branches |
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41 | of a company into a single network. Many so-called "vpn" solutions |
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42 | only create point-to-point tunnels, which in turn can be used to |
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43 | build larger networks. |
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44 | |
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45 | GVPE provides a true multi-point network in wich any number of nodes |
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46 | (at least a few dozen in practise, the theoretical limit is 4095 |
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47 | nodes) can participate. |
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48 | |
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49 | |
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50 | == GVPE DESIGN GOALS == |
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51 | |
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52 | : SIMPLE DESIGN |
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53 | Cipher, HMAC algorithms and other key parameters must be selected at |
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54 | compile time - this makes it possible to only link in algorithms you |
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55 | actually need. It also makes the crypto part of the source very |
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56 | transparent and easy to inspect, and last not least this makes it |
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57 | possible to hardcode the layout of all packets into the binary. GVPE |
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58 | goes a step further and internally reserves blocks of the same |
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59 | length for all packets, which virtually removes all possibilities of |
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60 | buffer overflows, as there is only a single type of buffer and it's |
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61 | always of fixed length. |
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62 | |
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63 | : EASY TO SETUP |
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64 | A few lines of config (the config file is shared unmodified between |
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65 | all hosts) and a single run of ``gvpectrl'' to generate the keys |
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66 | suffices to make it work. |
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67 | |
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68 | : MAC-BASED SECURITY |
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69 | Since every host has it's own private key, other hosts cannot spoof |
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70 | traffic from this host. That makes it possible to filter packet by |
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71 | MAC address, e.g. to ensure that packets from a specific IP address |
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72 | come, in fact, from a specific host that is associated with that IP |
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73 | and not from another host. |
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74 | |
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75 | |
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76 | ==== PROGRAMS ==== |
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77 | |
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78 | Vpe comes with two programs: one daemon (``gvpe'') and one control |
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79 | program (``gvpectrl''). |
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80 | |
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81 | : gvpectrl |
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82 | Is used to generate the keys, check and give an overview of of the |
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83 | configuration and contorl the daemon (restarting etc.). |
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84 | |
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85 | : gvpe |
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86 | Is the daemon used to establish and maintain connections to the |
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87 | other network members. It should be run on the gateway machine. |
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88 | |
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89 | |
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90 | ==== COMPILETIME CONFIGURATION ==== |
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91 | |
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92 | Please have a look at the ``gvpe.osdep(5)'' manpage for |
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93 | platform-specific information. |
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94 | |
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95 | Here are a few recipes for compiling your gvpe, showing the extremes |
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96 | (fast, small, insecure OR slow, large, more secure), between you should |
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97 | choose: |
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98 | |
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99 | |
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100 | == AS LOW PACKET OVERHEAD AS POSSIBLE == |
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101 | |
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102 | ./configure --enable-hmac-length=4 --enable-rand-length=0 |
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103 | |
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104 | Minimize the header overhead of VPN packets (the above will result in |
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105 | only 4 bytes of overhead over the raw ethernet frame). This is a |
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106 | insecure configuration because a HMAC length of 4 makes collision |
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107 | attacks based on the birthday paradox easy, though. |
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108 | |
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109 | |
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110 | == MINIMIZE CPU TIME REQUIRED == |
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111 | |
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112 | ./configure --enable-cipher=bf --enable-digest=md4 |
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113 | |
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114 | Use the fastest cipher and digest algorithms currently available in |
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115 | gvpe. MD4 has been broken and is quite insecure, though. |
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116 | |
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117 | |
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118 | == MAXIMIZE SECURITY == |
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119 | |
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120 | ./configure --enable-hmac-length=16 --enable-rand-length=8 --enable-digest=sha1 |
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121 | |
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122 | This uses a 16 byte HMAC checksum to authenticate packets (I guess 8-12 |
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123 | would also be pretty secure ;) and will additionally prefix each packet |
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124 | with 8 bytes of random data. In the long run, people should move to |
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125 | SHA-224 and beyond, but support in openssl is missing as of writing this |
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126 | document. |
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127 | |
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128 | In general, remember that AES-128 seems to be more secure and faster |
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129 | than AES-192 or AES-256, more randomness helps against sniffing and a |
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130 | longer HMAC helps against spoofing. MD4 is a fast digest, SHA1 or |
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131 | RIPEMD160 are better, and Blowfish is a fast cipher (and also quite |
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132 | secure). |
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133 | |
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134 | |
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135 | ==== HOW TO SET UP A SIMPLE VPN ==== |
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136 | |
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137 | In this section I will describe how to get a simple VPN consisting of |
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138 | three hosts up and running. |
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139 | |
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140 | |
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141 | == STEP 1: configuration == |
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142 | |
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143 | First you have to create a daemon configuation file and put it into the |
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144 | configuration directory. This is usually ``/etc/gvpe'', depending on how |
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145 | you configured gvpe, and can be overwritten using the ``-c'' commandline |
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146 | switch. |
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147 | |
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148 | Put the following lines into ``/etc/gvpe/gvpe.conf'': |
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149 | |
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150 | udp-port = 50000 # the external port to listen on (configure your firewall) |
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151 | mtu = 1400 # minimum MTU of all outgoing interfaces on all hosts |
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152 | ifname = vpn0 # the local network device name |
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153 | |
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154 | node = first # just a nickname |
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155 | hostname = first.example.net # the DNS name or IP address of the host |
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156 | |
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157 | node = second |
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158 | hostname = 133.55.82.9 |
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159 | |
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160 | node = third |
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161 | hostname = third.example.net |
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162 | |
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163 | The only other file neccessary if the ``if-up'' script that initializes |
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164 | the local ethernet interface. Put the following lines into |
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165 | ``/etc/gvpe/if-up'' and make it execute (``chmod 755 /etc/gvpe/if-up''): |
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166 | |
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167 | #!/bin/sh |
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168 | ip link set $IFNAME address $MAC mtu $MTU up |
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169 | [ $NODENAME = first ] && ip addr add 10.0.1.1 dev $IFNAME |
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170 | [ $NODENAME = second ] && ip addr add 10.0.2.1 dev $IFNAME |
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171 | [ $NODENAME = third ] && ip addr add 10.0.3.1 dev $IFNAME |
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172 | ip route add 10.0.0.0/16 dev $IFNAME |
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173 | |
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174 | This script will give each node a different IP address in the |
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175 | ``10.0/16'' network. The internal network (e.g. the ``eth0'' interface) |
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176 | should then be set to a subset of that network, e.g. ``10.0.1.0/24'' on |
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177 | node ``first'', ``10.0.2.0/24'' on node ``second'', and so on. |
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178 | |
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179 | By enabling routing on the gateway host that runs ``gvpe'' all nodes |
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180 | will be able to reach the other nodes. You can, of course, also use |
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181 | proxy arp or other means of pseudo-bridging (or even real briding), or |
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182 | (best) full routing - the choice is yours. |
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183 | |
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184 | |
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185 | == STEP 2: create the RSA key pairs for all hosts == |
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186 | |
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187 | Run the following command to generate all key pairs (that might take a |
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188 | while): |
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189 | |
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190 | gvpectrl -c /etc/gvpe -g |
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191 | |
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192 | This command will put the public keys into |
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193 | ``/etc/gvpe/pubkeys/*nodename*'' and the private keys into |
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194 | ``/etc/gvpe/hostkeys/*nodename*''. |
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195 | |
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196 | |
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197 | == STEP 3: distribute the config files to all nodes == |
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198 | |
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199 | Now distribute the config files to the other nodes. This should be done |
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200 | in two steps, since the private keys should not be distributed. The |
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201 | example uses rsync-over-ssh |
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202 | |
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203 | First all the config files without the hostkeys should be distributed: |
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204 | |
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205 | rsync -avzessh /etc/gvpe first.example.net:/etc/. --exclude hostkeys |
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206 | rsync -avzessh /etc/gvpe 133.55.82.9:/etc/. --exclude hostkeys |
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207 | rsync -avzessh /etc/gvpe third.example.net:/etc/. --exclude hostkeys |
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208 | |
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209 | Then the hostkeys should be copied: |
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210 | |
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211 | rsync -avzessh /etc/gvpe/hostkeys/first first.example.net:/etc/hostkey |
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212 | rsync -avzessh /etc/gvpe/hostkeys/second 133.55.82.9:/etc/hostkey |
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213 | rsync -avzessh /etc/gvpe/hostkeys/third third.example.net:/etc/hostkey |
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214 | |
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215 | You should now check the configration by issuing the command ``gvpectrl |
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216 | -c /etc/gvpe -s'' on each node and verify it's output. |
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217 | |
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218 | |
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219 | == STEP 4: starting gvpe == |
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220 | |
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221 | You should then start gvpe on each node by issuing a command like: |
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222 | |
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223 | gvpe -D -linfo first # first is the nodename |
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224 | |
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225 | This will make the gvpe stay in foreground. You should then see |
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226 | "connection established" messages. If you don't see them check your |
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227 | firewall and routing (use tcpdump ;). |
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228 | |
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229 | If this works you should check your networking setup by pinging various |
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230 | endpoints. |
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231 | |
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232 | To make gvpe run more permanently you can either run it as a daemon (by |
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233 | starting it without the ``-D'' switch), or, much better, from your |
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234 | inittab. I use a line like this on my systems: |
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235 | |
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236 | t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1 |
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237 | |
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238 | |
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239 | == STEP 5: enjoy == |
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240 | |
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241 | ... and play around. Sending a -HUP (``gvpectrl -kHUP'') to the daemon |
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242 | will make it try to connect to all other nodes again. If you run it from |
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243 | inittab, as is recommended, ``gvpectrl -k'' (or simply ``killall gvpe'') |
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244 | will kill the daemon, start it again, making it read it's configuration |
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245 | files again. |
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246 | |
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247 | |
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248 | ==== SEE ALSO ==== |
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249 | |
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250 | gvpe.osdep(5) for OS-depedendent information, gvpe.conf(5), gvpectrl(8), |
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251 | and for a description of the transports, protocol, and routing |
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252 | algorithm, gvpe.protocol(7). |
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253 | |
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254 | The GVPE mailinglist, at <http://lists.schmorp.de/>, or |
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255 | ``gvpe@lists.schmorp.de''. |
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256 | |
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257 | |
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258 | ==== AUTHOR ==== |
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259 | |
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260 | Marc Lehmann <gvpe@schmorp.de> |
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261 | |
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262 | |
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263 | ==== COPYRIGHTS AND LICENSES ==== |
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264 | |
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265 | GVPE itself is distributed under the GENERAL PUBLIC LICENSE (see the |
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266 | file COPYING that should be part of your distribution). |
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267 | |
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268 | In some configurations it uses modified versions of the tinc vpn suite, |
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269 | which is also available under the GENERAL PUBLIC LICENSE. |
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270 | |