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Revision 1.2 by pcg, Tue Mar 15 19:23:33 2005 UTC

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127.\} 127.\}
128.rm #[ #] #H #V #F C 128.rm #[ #] #H #V #F C
129.\" ======================================================================== 129.\" ========================================================================
130.\" 130.\"
131.IX Title "GVPE.PROTOCOL 7" 131.IX Title "GVPE.PROTOCOL 7"
132.TH GVPE.PROTOCOL 7 "2004-06-11" "1.7" "GNU Virtual Private Ethernet" 132.TH GVPE.PROTOCOL 7 "2005-03-15" "1.8" "GNU Virtual Private Ethernet"
133.SH "The GNU-VPE Protocol" 133.SH "The GNU-VPE Protocols"
134.IX Header "The GNU-VPE Protocol" 134.IX Header "The GNU-VPE Protocols"
135.SH "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
138protocol which is used to authenticate tunnels and send encrypted data
139packets. This protocol is described in more detail the second part of this
140document.
141.PP
142The first part of this document describes the transport protocols which
143are used by \s-1GVPE\s0 to send it's data packets over the network.
144.SH "PART 1: Tansport protocols"
145.IX Header "PART 1: Tansport protocols"
146.Sh "\s-1RAW\s0 \s-1IP\s0"
147.IX Subsection "RAW IP"
148.Sh "\s-1ICMP\s0"
149.IX Subsection "ICMP"
150.Sh "\s-1UDP\s0"
151.IX Subsection "UDP"
152.Sh "\s-1TCP\s0"
153.IX Subsection "TCP"
154.Sh "\s-1DNS\s0"
155.IX Subsection "DNS"
156.SH "PART 2: The GNU VPE protocol"
157.IX Header "PART 2: The GNU VPE protocol"
158This section, unfortunately, is not yet finished, although the protocol
159is stable (until bugs in the cryptography are found, which will likely
160completely change the following description). Nevertheless, it should give
161you some overview over the protocol.
135.Sh "Anatomy of a \s-1VPN\s0 packet" 162.Sh "Anatomy of a \s-1VPN\s0 packet"
136.IX Subsection "Anatomy of a VPN packet" 163.IX Subsection "Anatomy of a VPN packet"
137The exact layout and field lengths of a \s-1VPN\s0 packet is determined at 164The exact layout and field lengths of a \s-1VPN\s0 packet is determined at
138compiletime and doesn't change. The same structure is used for all 165compiletime and doesn't change. The same structure is used for all
139protocols, be it rawip or tcp. 166transort protocols, be it \s-1RAWIP\s0 or \s-1TCP\s0.
140.PP 167.PP
141.Vb 3 168.Vb 3
142\& +------+------+--------+------+ 169\& +------+------+--------+------+
143\& | HMAC | TYPE | SRCDST | DATA | 170\& | HMAC | TYPE | SRCDST | DATA |
144\& +------+------+--------+------+ 171\& +------+------+--------+------+
145.Ve 172.Ve
146.PP 173.PP
147The \s-1HMAC\s0 field is present in all packets, even if not used (e.g. in auth 174The \s-1HMAC\s0 field is present in all packets, even if not used (e.g. in auth
148request packets), in which case it is set to all zeroes. The checksum 175request packets), in which case it is set to all zeroes. The checksum
149itself is over the \s-1TYPE\s0, \s-1SRCDST\s0 and \s-1DATA\s0 fields in all cases. 176itself is calculated over the \s-1TYPE\s0, \s-1SRCDST\s0 and \s-1DATA\s0 fields in all cases.
150.PP 177.PP
151The \s-1TYPE\s0 field is a single byte and determines the purpose of the packet 178The \s-1TYPE\s0 field is a single byte and determines the purpose of the packet
152(e.g. \s-1RESET\s0, \s-1COMPRESSED/UNCOMPRESSED\s0 \s-1DATA\s0, \s-1PING\s0, \s-1AUTH\s0 \s-1REQUEST/RESPONSE\s0, 179(e.g. \s-1RESET\s0, \s-1COMPRESSED/UNCOMPRESSED\s0 \s-1DATA\s0, \s-1PING\s0, \s-1AUTH\s0 \s-1REQUEST/RESPONSE\s0,
153\&\s-1CONNECT\s0 \s-1REQUEST/INFO\s0 etc.). 180\&\s-1CONNECT\s0 \s-1REQUEST/INFO\s0 etc.).
154.PP 181.PP
155\&\s-1SRCDST\s0 is a three byte field which contains the source and destination 182\&\s-1SRCDST\s0 is a three byte field which contains the source and destination
156node ids (12 bits each). The protocol does not yet scale well beyond 30+ 183node ids (12 bits each). The protocol does not yet scale well beyond 30+
157hosts, since all hosts connect to each other on startup. But if restarts 184hosts, since all hosts must connect to each other once on startup. But if
158are rare or tolerable and most connections are on demand, larger networks 185restarts are rare or tolerable and most connections are on demand, much
159are possible. 186larger networks are feasible.
160.PP 187.PP
161The \s-1DATA\s0 portion differs between each packet type, naturally, and is the 188The \s-1DATA\s0 portion differs between each packet type, naturally, and is the
162only part that can be encrypted. Data packets contain more fields, as 189only part that can be encrypted. Data packets contain more fields, as
163shown: 190shown:
164.PP 191.PP
… …
171\&\s-1RAND\s0 is a sequence of fully random bytes, used to increase the entropy of 198\&\s-1RAND\s0 is a sequence of fully random bytes, used to increase the entropy of
172the data for encryption purposes. 199the data for encryption purposes.
173.PP 200.PP
174\&\s-1SEQNO\s0 is a 32\-bit sequence number. It is negotiated at every connection 201\&\s-1SEQNO\s0 is a 32\-bit sequence number. It is negotiated at every connection
175initialization and starts at some random 31 bit value. \s-1VPE\s0 currently uses 202initialization and starts at some random 31 bit value. \s-1VPE\s0 currently uses
176a sliding window of 512 packets to detect reordering, duplication and 203a sliding window of 512 packets/sequence numbers to detect reordering,
177reply attacks. 204duplication and reply attacks.
178.Sh "The authentification protocol" 205.Sh "The authentification protocol"
179.IX Subsection "The authentification protocol" 206.IX Subsection "The authentification protocol"
180Before hosts can exchange packets, they need to establish authenticity of 207Before hosts can exchange packets, they need to establish authenticity of
181the other side and a key. Every host has a private \s-1RSA\s0 key and the public 208the other side and a key. Every host has a private \s-1RSA\s0 key and the public
182\&\s-1RSA\s0 keys of all other hosts. 209\&\s-1RSA\s0 keys of all other hosts.
… …
194hash and the id, which will expire after 120 seconds), it will start to 221hash and the id, which will expire after 120 seconds), it will start to
195accept data packets from the destination host. 222accept data packets from the destination host.
196.PP 223.PP
197This means that a host can only initate a simplex connection, telling the 224This means that a host can only initate a simplex connection, telling the
198other side the key it has to use when it sends packets. The challenge 225other side the key it has to use when it sends packets. The challenge
199reply is only used to set the current \s-1IP\s0 address and protocol parameters. 226reply is only used to set the current \s-1IP\s0 address of the other side and
227protocol parameters.
200.PP 228.PP
201The protocol here is completely symmetric, so to be able to send packets 229This protocol is completely symmetric, so to be able to send packets the
202the destination host must send a challenge in the exact same way as 230destination host must send a challenge in the exact same way as already
203already described (so, in essence, two simplex connections are created per 231described (so, in essence, two simplex connections are created per host
204host pair). 232pair).
205.Sh "Retrying" 233.Sh "Retrying"
206.IX Subsection "Retrying" 234.IX Subsection "Retrying"
207When there is no response to an auth request, the host will send auth 235When there is no response to an auth request, the host will send auth
208requests in bursts with an exponential backoff. After some time it will 236requests in bursts with an exponential backoff. After some time it will
209resort to \s-1PING\s0 packets, which are very small (8 byte) and lightweight (no 237resort to \s-1PING\s0 packets, which are very small (8 bytes) and lightweight
210\&\s-1RSA\s0 operations). A host that receives ping requests from an unconnected 238(no \s-1RSA\s0 operations required). A host that receives ping requests from an
211peer will respond by trying to create a connection. 239unconnected peer will respond by trying to create a connection.
212.PP 240.PP
213In addition to the exponential backoff, there is a global rate-limit on 241In addition to the exponential backoff, there is a global rate-limit on
214a per-ip base. It allows long bursts but will limit total packet rate to 242a per-IP base. It allows long bursts but will limit total packet rate to
215something like one control packet every ten seconds, to avoid accidental 243something like one control packet every ten seconds, to avoid accidental
216floods due to protocol problems (like a rsa key file mismatch between two 244floods due to protocol problems (like a \s-1RSA\s0 key file mismatch between two
217hosts). 245hosts).
218.Sh "Routing and Protocol translation" 246.Sh "Routing and Protocol translation"
219.IX Subsection "Routing and Protocol translation" 247.IX Subsection "Routing and Protocol translation"
220The gvpe routing algorithm is easy: there isn't any routing. \s-1GVPE\s0 always 248The gvpe routing algorithm is easy: there isn't any routing. \s-1GVPE\s0 always
221tries to establish direct connections, if the protocol abilities of the 249tries to establish direct connections, if the protocol abilities of the

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