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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 |
| … | |
… | |
| 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. |
| … | |
… | |
| 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 |
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| 232 | pair). |
305 | pair). |
| 233 | .Sh "Retrying" |
306 | .Sh "Retrying" |
| 234 | .IX Subsection "Retrying" |
307 | .IX Subsection "Retrying" |
| 235 | When there is no response to an auth request, the host will send auth |
308 | When there is no response to an auth request, the host will send auth |
| 236 | requests in bursts with an exponential backoff. After some time it will |
309 | requests in bursts with an exponential backoff. After some time it will |
| 237 | resort to \s-1PING\s0 packets, which are very small (8 bytes) and lightweight |
310 | resort to \s-1PING\s0 packets, which are very small (8 bytes + protocol header) |
| 238 | (no \s-1RSA\s0 operations required). A host that receives ping requests from an |
311 | and lightweight (no \s-1RSA\s0 operations required). A host that receives ping |
| 239 | unconnected peer will respond by trying to create a connection. |
312 | requests from an unconnected peer will respond by trying to create a |
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313 | connection. |
| 240 | .PP |
314 | .PP |
| 241 | In addition to the exponential backoff, there is a global rate-limit on |
315 | In addition to the exponential backoff, there is a global rate-limit on |
| 242 | a per-IP base. It allows long bursts but will limit total packet rate to |
316 | a per-IP base. It allows long bursts but will limit total packet rate to |
| 243 | something like one control packet every ten seconds, to avoid accidental |
317 | something like one control packet every ten seconds, to avoid accidental |
| 244 | floods due to protocol problems (like a \s-1RSA\s0 key file mismatch between two |
318 | floods due to protocol problems (like a \s-1RSA\s0 key file mismatch between two |
| 245 | hosts). |
319 | hosts). |
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320 | .PP |
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321 | The intervals between retries are limited by the \f(CW\*(C`max\-retry\*(C'\fR |
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322 | configuration value. A node with \f(CW\*(C`connect\*(C'\fR = \f(CW\*(C`always\*(C'\fR will always retry, |
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323 | a node with \f(CW\*(C`connect\*(C'\fR = \f(CW\*(C`ondemand\*(C'\fR will only try (and re\-try) to connect |
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324 | as long as there are packets in the queue, usually this limits the retry |
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325 | period to \f(CW\*(C`max\-ttl\*(C'\fR seconds. |
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326 | .PP |
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327 | Sending packets over the \s-1VPN\s0 will reset the retry intervals as well, which |
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328 | means as long as somebody is trying to send packets to a given node, \s-1GVPE\s0 |
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329 | will try to connect every few seconds. |
| 246 | .Sh "Routing and Protocol translation" |
330 | .Sh "Routing and Protocol translation" |
| 247 | .IX Subsection "Routing and Protocol translation" |
331 | .IX Subsection "Routing and Protocol translation" |
| 248 | The gvpe routing algorithm is easy: there isn't any routing. \s-1GVPE\s0 always |
332 | The \s-1GVPE\s0 routing algorithm is easy: there isn't much routing to speak |
| 249 | tries to establish direct connections, if the protocol abilities of the |
333 | of: When routing packets to another node, \s-1GVPE\s0 trues the following |
| 250 | two hosts allow it. |
334 | options, in order: |
| 251 | .PP |
335 | .IP "If the two hosts should be able to reach each other directly (common protocol, port known), then \s-1GVPE\s0 will send the packet directly to the other node." 4 |
| 252 | If the two hosts should be able to reach each other (common protocol, ip |
336 | .IX Item "If the two hosts should be able to reach each other directly (common protocol, port known), then GVPE will send the packet directly to the other node." |
| 253 | and port all known), but cannot (network down), then there will be no |
337 | .PD 0 |
| 254 | connection, point. |
338 | .ie n .IP "If this isn't possible (e.g. because the node doesn't have a \*(C`hostname\*(C' or known port), but the nodes speak a common protocol and a router is available, then \s-1GVPE\s0 will ask a router to ""mediate"" between both nodes (see below)." 4 |
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339 | .el .IP "If this isn't possible (e.g. because the node doesn't have a \f(CW\*(C`hostname\*(C'\fR or known port), but the nodes speak a common protocol and a router is available, then \s-1GVPE\s0 will ask a router to ``mediate'' between both nodes (see below)." 4 |
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340 | .IX Item "If this isn't possible (e.g. because the node doesn't have a 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)." |
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341 | .ie n .IP "If a direct connection isn't possible (no common protocols) or forbidden (\*(C`deny\-direct\*(C'\fR) and there are any routers, then \s-1GVPE\s0 will try to send packets to the router with the highest priority that is connected already \fIand is able (as specified by the config file) to connect directly to the target node." 4 |
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342 | .el .IP "If a direct connection isn't possible (no common protocols) or forbidden (\f(CW\*(C`deny\-direct\*(C'\fR) and there are any routers, then \s-1GVPE\s0 will try to send packets to the router with the highest priority that is connected already \fIand\fR is able (as specified by the config file) to connect directly to the target node." 4 |
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343 | .IX Item "If a direct connection isn't possible (no common protocols) or forbidden (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 and is able (as specified by the config file) to connect directly to the target node." |
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344 | .IP "If no such router exists, then \s-1GVPE\s0 will simply send the packet to the node with the highest priority available." 4 |
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345 | .IX Item "If no such router exists, then GVPE will simply send the packet to the node with the highest priority available." |
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346 | .IP "Failing all that, the packet will be dropped." 4 |
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347 | .IX Item "Failing all that, the packet will be dropped." |
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348 | .PD |
| 255 | .PP |
349 | .PP |
| 256 | A host can usually declare itself unreachable directly by setting it's |
350 | A host can usually declare itself unreachable directly by setting it's |
| 257 | port number(s) to zero. It can declare other hosts as unreachable by using |
351 | port number(s) to zero. It can declare other hosts as unreachable by using |
| 258 | a config-file that disables all protocols for these other hosts. |
352 | a config-file that disables all protocols for these other hosts. Another |
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353 | option is to disable all protocols on that host in the other config files. |
| 259 | .PP |
354 | .PP |
| 260 | If two hosts cannot connect to each other because their \s-1IP\s0 address(es) |
355 | If two hosts cannot connect to each other because their \s-1IP\s0 address(es) |
| 261 | are not known (such as dialup hosts), one side will send a connection |
356 | are not known (such as dialup hosts), one side will send a \fImediated\fR |
| 262 | request to a router (routers must be configured to act as routers!), which |
357 | connection request to a router (routers must be configured to act as |
| 263 | will send both the originating and the destination host a connection info |
358 | routers!), which will send both the originating and the destination host |
| 264 | request with protocol information and \s-1IP\s0 address of the other host (if |
359 | a connection info request with protocol information and \s-1IP\s0 address of the |
| 265 | known). Both hosts will then try to establish a connection to the other |
360 | other host (if known). Both hosts will then try to establish a direct |
| 266 | peer, which is usually possible even when both hosts are behind a \s-1NAT\s0 |
361 | connection to the other peer, which is usually possible even when both |
| 267 | gateway. |
362 | hosts are behind a \s-1NAT\s0 gateway. |
| 268 | .PP |
363 | .PP |
| 269 | If the hosts cannot reach each other because they have no common protocol, |
364 | Routing via other nodes works because the \s-1SRCDST\s0 field is not encrypted, |
| 270 | the originator instead use the router with highest priority and matching |
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| 271 | protocol as peer. Since the \s-1SRCDST\s0 field is not encrypted, the router host |
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| 272 | can just forward the packet to the destination host. Since each host uses |
365 | so the router can just forward the packet to the destination host. Since |
| 273 | it's own private key, the router will not be able to decrypt or encrypt |
366 | each host uses it's own private key, the router will not be able to |
| 274 | packets, it will just act as a simple router and protocol translator. |
367 | decrypt or encrypt packets, it will just act as a simple router and |
| 275 | .PP |
368 | protocol translator. |
| 276 | When no router is connected, the host will aggressively try to connect to |
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| 277 | all routers, and if a router is asked for an unconnected host it will try |
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| 278 | to ask another router to establish the connection. |
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| 279 | .PP |
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| 280 | \&... more not yet written about the details of the routing, please bug me |
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| 281 | \&... |
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