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| 32 | .tr \(*W-|\(bv\*(Tr |
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| 131 | .IX Title "GVPE.PROTOCOL 7" |
131 | .IX Title "GVPE.PROTOCOL 7" |
| 132 | .TH GVPE.PROTOCOL 7 "2005-03-15" "1.8" "GNU Virtual Private Ethernet" |
132 | .TH GVPE.PROTOCOL 7 "2008-08-10" "2.2" "GNU Virtual Private Ethernet" |
| 133 | .SH "The GNU-VPE Protocols" |
133 | .SH "The GNU-VPE Protocols" |
| 134 | .IX Header "The GNU-VPE Protocols" |
134 | .IX Header "The GNU-VPE Protocols" |
| 135 | .SH "Overview" |
135 | .SH "Overview" |
| 136 | .IX Header "Overview" |
136 | .IX Header "Overview" |
| 137 | \&\s-1GVPE\s0 can make use of a number of protocols. One of them is the \s-1GNU\s0 \s-1VPE\s0 |
137 | \&\s-1GVPE\s0 can make use of a number of protocols. One of them is the \s-1GNU\s0 \s-1VPE\s0 |
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| 139 | packets. This protocol is described in more detail the second part of this |
139 | packets. This protocol is described in more detail the second part of this |
| 140 | document. |
140 | document. |
| 141 | .PP |
141 | .PP |
| 142 | The first part of this document describes the transport protocols which |
142 | The first part of this document describes the transport protocols which |
| 143 | are used by \s-1GVPE\s0 to send it's data packets over the network. |
143 | are used by \s-1GVPE\s0 to send it's data packets over the network. |
| 144 | .SH "PART 1: Tansport protocols" |
144 | .SH "PART 1: Transport protocols" |
| 145 | .IX Header "PART 1: Tansport protocols" |
145 | .IX Header "PART 1: Transport protocols" |
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146 | \&\s-1GVPE\s0 offers a wide range of transport protocols that can be used to |
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147 | interchange data between nodes. Protocols differ in their overhead, speed, |
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148 | reliability, and robustness. |
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149 | .PP |
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150 | The following sections describe each transport protocol in more |
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151 | detail. They are sorted by overhead/efficiency, the most efficient |
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152 | transport is listed first: |
| 146 | .Sh "\s-1RAW\s0 \s-1IP\s0" |
153 | .Sh "\s-1RAW\s0 \s-1IP\s0" |
| 147 | .IX Subsection "RAW IP" |
154 | .IX Subsection "RAW IP" |
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155 | This protocol is the best choice, performance\-wise, as the minimum |
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156 | overhead per packet is only 38 bytes. |
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157 | .PP |
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158 | It works by sending the \s-1VPN\s0 payload using raw ip frames (using the |
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159 | protocol set by \f(CW\*(C`ip\-proto\*(C'\fR). |
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160 | .PP |
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161 | Using raw ip frames has the drawback that many firewalls block \*(L"unknown\*(R" |
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162 | protocols, so this transport only works if you have full \s-1IP\s0 connectivity |
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163 | between nodes. |
| 148 | .Sh "\s-1ICMP\s0" |
164 | .Sh "\s-1ICMP\s0" |
| 149 | .IX Subsection "ICMP" |
165 | .IX Subsection "ICMP" |
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166 | This protocol offers very low overhead (minimum 42 bytes), and can |
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167 | sometimes tunnel through firewalls when other protocols can not. |
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168 | .PP |
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169 | It works by prepending an \s-1ICMP\s0 header with type \f(CW\*(C`icmp\-type\*(C'\fR and a code |
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170 | of \f(CW255\fR. The default \f(CW\*(C`icmp\-type\*(C'\fR is \f(CW\*(C`echo\-reply\*(C'\fR, so the resulting |
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171 | packets look like echo replies, which looks rather strange to network |
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172 | admins. |
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173 | .PP |
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174 | This transport should only be used if other transports (i.e. raw ip) are |
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175 | not available or undesirable (due to their overhead). |
| 150 | .Sh "\s-1UDP\s0" |
176 | .Sh "\s-1UDP\s0" |
| 151 | .IX Subsection "UDP" |
177 | .IX Subsection "UDP" |
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178 | This is a good general choice for the transport protocol as \s-1UDP\s0 packets |
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179 | tunnel well through most firewalls and routers, and the overhead per |
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180 | packet is moderate (minimum 58 bytes). |
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181 | .PP |
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182 | It should be used if \s-1RAW\s0 \s-1IP\s0 is not available. |
| 152 | .Sh "\s-1TCP\s0" |
183 | .Sh "\s-1TCP\s0" |
| 153 | .IX Subsection "TCP" |
184 | .IX Subsection "TCP" |
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185 | This protocol is a very bad choice, as it not only has high overhead (more |
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186 | than 60 bytes), but the transport also retries on it's own, which leads |
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187 | to congestion when the link has moderate packet loss (as both the \s-1TCP\s0 |
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188 | transport and the tunneled traffic will retry, increasing congestion more |
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189 | and more). It also has high latency and is quite inefficient. |
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190 | .PP |
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191 | It's only useful when tunneling through firewalls that block better |
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192 | protocols. If a node doesn't have direct internet access but a \s-1HTTP\s0 proxy |
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193 | that supports the \s-1CONNECT\s0 method it can be used to tunnel through a web |
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194 | proxy. For this to work, the \f(CW\*(C`tcp\-port\*(C'\fR should be \f(CW443\fR (\f(CW\*(C`https\*(C'\fR), as |
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195 | most proxies do not allow connections to other ports. |
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196 | .PP |
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197 | It is an abuse of the usage a proxy was designed for, so make sure you are |
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198 | allowed to use it for \s-1GVPE\s0. |
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199 | .PP |
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200 | This protocol also has server and client sides. If the \f(CW\*(C`tcp\-port\*(C'\fR is |
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201 | set to zero, other nodes cannot connect to this node directly. If the |
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202 | \&\f(CW\*(C`tcp\-port\*(C'\fR is non\-zero, the node can act both as a client as well as a |
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203 | server. |
| 154 | .Sh "\s-1DNS\s0" |
204 | .Sh "\s-1DNS\s0" |
| 155 | .IX Subsection "DNS" |
205 | .IX Subsection "DNS" |
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206 | \&\fB\s-1WARNING:\s0\fR Parsing and generating \s-1DNS\s0 packets is rather tricky. The code |
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207 | almost certainly contains buffer overflows and other, likely exploitable, |
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208 | bugs. You have been warned. |
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209 | .PP |
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210 | This is the worst choice of transport protocol with respect to overhead |
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211 | (overhead can be 2\-3 times higher than the transferred data), and latency |
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212 | (which can be many seconds). Some \s-1DNS\s0 servers might not be prepared to |
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213 | handle the traffic and drop or corrupt packets. The client also has to |
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214 | constantly poll the server for data, so the client will constantly create |
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215 | traffic even if it doesn't need to transport packets. |
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216 | .PP |
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217 | In addition, the same problems as the \s-1TCP\s0 transport also plague this |
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218 | protocol. |
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219 | .PP |
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220 | It's only use is to tunnel through firewalls that do not allow direct |
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221 | internet access. Similar to using a \s-1HTTP\s0 proxy (as the \s-1TCP\s0 transport |
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222 | does), it uses a local \s-1DNS\s0 server/forwarder (given by the \f(CW\*(C`dns\-forw\-host\*(C'\fR |
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223 | configuration value) as a proxy to send and receive data as a client, |
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224 | and an \f(CW\*(C`NS\*(C'\fR record pointing to the \s-1GVPE\s0 server (as given by the |
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225 | \&\f(CW\*(C`dns\-hostname\*(C'\fR directive). |
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226 | .PP |
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227 | The only good side of this protocol is that it can tunnel through most |
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228 | firewalls mostly undetected, iff the local \s-1DNS\s0 server/forwarder is sane |
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229 | (which is true for most routers, \s-1WLAN\s0 gateways and nameservers). |
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230 | .PP |
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231 | Finetuning needs to be done by editing \f(CW\*(C`src/vpn_dns.C\*(C'\fR directly. |
| 156 | .SH "PART 2: The GNU VPE protocol" |
232 | .SH "PART 2: The GNU VPE protocol" |
| 157 | .IX Header "PART 2: The GNU VPE protocol" |
233 | .IX Header "PART 2: The GNU VPE protocol" |
| 158 | This section, unfortunately, is not yet finished, although the protocol |
234 | This section, unfortunately, is not yet finished, although the protocol |
| 159 | is stable (until bugs in the cryptography are found, which will likely |
235 | is stable (until bugs in the cryptography are found, which will likely |
| 160 | completely change the following description). Nevertheless, it should give |
236 | completely change the following description). Nevertheless, it should give |
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| 164 | The exact layout and field lengths of a \s-1VPN\s0 packet is determined at |
240 | The exact layout and field lengths of a \s-1VPN\s0 packet is determined at |
| 165 | compiletime and doesn't change. The same structure is used for all |
241 | compiletime and doesn't change. The same structure is used for all |
| 166 | transort protocols, be it \s-1RAWIP\s0 or \s-1TCP\s0. |
242 | transort protocols, be it \s-1RAWIP\s0 or \s-1TCP\s0. |
| 167 | .PP |
243 | .PP |
| 168 | .Vb 3 |
244 | .Vb 3 |
| 169 | \& +------+------+--------+------+ |
245 | \& +\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-\-+\-\-\-\-\-\-+ |
| 170 | \& | HMAC | TYPE | SRCDST | DATA | |
246 | \& | HMAC | TYPE | SRCDST | DATA | |
| 171 | \& +------+------+--------+------+ |
247 | \& +\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-\-+\-\-\-\-\-\-+ |
| 172 | .Ve |
248 | .Ve |
| 173 | .PP |
249 | .PP |
| 174 | The \s-1HMAC\s0 field is present in all packets, even if not used (e.g. in auth |
250 | The \s-1HMAC\s0 field is present in all packets, even if not used (e.g. in auth |
| 175 | request packets), in which case it is set to all zeroes. The checksum |
251 | request packets), in which case it is set to all zeroes. The checksum |
| 176 | itself is calculated over the \s-1TYPE\s0, \s-1SRCDST\s0 and \s-1DATA\s0 fields in all cases. |
252 | itself is calculated over the \s-1TYPE\s0, \s-1SRCDST\s0 and \s-1DATA\s0 fields in all cases. |
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| 178 | The \s-1TYPE\s0 field is a single byte and determines the purpose of the packet |
254 | The \s-1TYPE\s0 field is a single byte and determines the purpose of the packet |
| 179 | (e.g. \s-1RESET\s0, \s-1COMPRESSED/UNCOMPRESSED\s0 \s-1DATA\s0, \s-1PING\s0, \s-1AUTH\s0 \s-1REQUEST/RESPONSE\s0, |
255 | (e.g. \s-1RESET\s0, \s-1COMPRESSED/UNCOMPRESSED\s0 \s-1DATA\s0, \s-1PING\s0, \s-1AUTH\s0 \s-1REQUEST/RESPONSE\s0, |
| 180 | \&\s-1CONNECT\s0 \s-1REQUEST/INFO\s0 etc.). |
256 | \&\s-1CONNECT\s0 \s-1REQUEST/INFO\s0 etc.). |
| 181 | .PP |
257 | .PP |
| 182 | \&\s-1SRCDST\s0 is a three byte field which contains the source and destination |
258 | \&\s-1SRCDST\s0 is a three byte field which contains the source and destination |
| 183 | node ids (12 bits each). The protocol does not yet scale well beyond 30+ |
259 | node IDs (12 bits each). |
| 184 | hosts, since all hosts must connect to each other once on startup. But if |
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| 185 | restarts are rare or tolerable and most connections are on demand, much |
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| 186 | larger networks are feasible. |
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| 187 | .PP |
260 | .PP |
| 188 | The \s-1DATA\s0 portion differs between each packet type, naturally, and is the |
261 | The \s-1DATA\s0 portion differs between each packet type, naturally, and is the |
| 189 | only part that can be encrypted. Data packets contain more fields, as |
262 | only part that can be encrypted. Data packets contain more fields, as |
| 190 | shown: |
263 | shown: |
| 191 | .PP |
264 | .PP |
| 192 | .Vb 3 |
265 | .Vb 3 |
| 193 | \& +------+------+--------+------+-------+------+ |
266 | \& +\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-+\-\-\-\-\-\-+ |
| 194 | \& | HMAC | TYPE | SRCDST | RAND | SEQNO | DATA | |
267 | \& | HMAC | TYPE | SRCDST | RAND | SEQNO | DATA | |
| 195 | \& +------+------+--------+------+-------+------+ |
268 | \& +\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-+\-\-\-\-\-\-+ |
| 196 | .Ve |
269 | .Ve |
| 197 | .PP |
270 | .PP |
| 198 | \&\s-1RAND\s0 is a sequence of fully random bytes, used to increase the entropy of |
271 | \&\s-1RAND\s0 is a sequence of fully random bytes, used to increase the entropy of |
| 199 | the data for encryption purposes. |
272 | the data for encryption purposes. |
| 200 | .PP |
273 | .PP |
| 201 | \&\s-1SEQNO\s0 is a 32\-bit sequence number. It is negotiated at every connection |
274 | \&\s-1SEQNO\s0 is a 32\-bit sequence number. It is negotiated at every connection |
| 202 | initialization and starts at some random 31 bit value. \s-1VPE\s0 currently uses |
275 | initialization and starts at some random 31 bit value. \s-1VPE\s0 currently uses |
| 203 | a sliding window of 512 packets/sequence numbers to detect reordering, |
276 | a sliding window of 512 packets/sequence numbers to detect reordering, |
| 204 | duplication and reply attacks. |
277 | duplication and replay attacks. |
| 205 | .Sh "The authentification protocol" |
278 | .Sh "The authentication protocol" |
| 206 | .IX Subsection "The authentification protocol" |
279 | .IX Subsection "The authentication protocol" |
| 207 | Before hosts can exchange packets, they need to establish authenticity of |
280 | Before hosts can exchange packets, they need to establish authenticity of |
| 208 | the other side and a key. Every host has a private \s-1RSA\s0 key and the public |
281 | the other side and a key. Every host has a private \s-1RSA\s0 key and the public |
| 209 | \&\s-1RSA\s0 keys of all other hosts. |
282 | \&\s-1RSA\s0 keys of all other hosts. |
| 210 | .PP |
283 | .PP |
| 211 | A host establishes a simplex connection by sending the other host a |
284 | A host establishes a simplex connection by sending the other host an |
| 212 | \&\s-1RSA\s0 encrypted challenge containing a random challenge (consisting of |
285 | \&\s-1RSA\s0 encrypted challenge containing a random challenge (consisting of |
| 213 | the encryption key to use when sending packets, more random data and |
286 | the encryption key to use when sending packets, more random data and |
| 214 | \&\s-1PKCS1_OAEP\s0 padding) and a random 16 byte \*(L"challenge\-id\*(R" (used to detect |
287 | \&\s-1PKCS1_OAEP\s0 padding) and a random 16 byte \*(L"challenge\-id\*(R" (used to detect |
| 215 | duplicate auth packets). The destination host will respond by replying |
288 | duplicate auth packets). The destination host will respond by replying |
| 216 | with an (unencrypted) \s-1RIPEMD160\s0 hash of the decrypted challenge, which |
289 | with an (unencrypted) \s-1RIPEMD160\s0 hash of the decrypted challenge, which |
| 217 | will authentify that host. The destination host will also set the outgoing |
290 | will authenticate that host. The destination host will also set the |
| 218 | encryption parameters as given in the packet. |
291 | outgoing encryption parameters as given in the packet. |
| 219 | .PP |
292 | .PP |
| 220 | When the source host receives a correct auth reply (by verifying the |
293 | When the source host receives a correct auth reply (by verifying the |
| 221 | hash and the id, which will expire after 120 seconds), it will start to |
294 | hash and the id, which will expire after 120 seconds), it will start to |
| 222 | accept data packets from the destination host. |
295 | accept data packets from the destination host. |
| 223 | .PP |
296 | .PP |
