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33 .\" Author: Archie Cobbs <archie@FreeBSD.org>
36 .\" $Whistle: ng_ppp.8,v 1.3 1999/01/25 23:46:27 archie Exp $
43 .Nd PPP protocol netgraph node type
49 node type performs multiplexing for the PPP protocol.
50 It handles only packets that contain data, and forwards protocol negotiation
51 and control packets to a separate controlling entity (e.g., a
53 This approach combines the fast dispatch of
54 kernel implementations with the configuration flexibility of a
55 user-land implementations.
56 The PPP node type directly supports
57 multi-link PPP, Van Jacobson compression, PPP compression, PPP
58 encryption, and the IP, IPX, and AppleTalk protocols.
59 A single PPP node corresponds to one PPP multi-link bundle.
61 There is a separate hook for each PPP link in the bundle, plus
62 several hooks corresponding to the directly supported protocols.
63 For compression and encryption, separate attached nodes are required
64 to do the actual work.
65 The node type used will of course depend on the algorithm negotiated.
68 hook which is used to handle any protocol not directly supported
70 This includes all of the control protocols: LCP, IPCP,
72 Typically this node is connected to a user-land daemon via a
75 .Sh ENABLING FUNCTIONALITY
76 In general, the PPP node enables a specific link or functionality when
78 .Dv NGM_PPP_SET_CONFIG
79 message has been received which enables it, and
80 (b) the corresponding hook(s) are connected.
81 This allows the controlling entity to use either method (a) or (b)
82 (or both) to control the node's behavior.
83 When a link is connected but disabled, traffic can still flow on
88 During normal operation, the individual PPP links are connected to hooks
94 These device-independent hooks transmit and receive full PPP
95 frames, which include the PPP protocol, address, control, and
96 information fields, but no checksum or other link-specific fields.
98 On outgoing frames, when protocol compression
99 has been enabled and the protocol number is suitable for compression,
100 the protocol field will be compressed (i.e., sent as one byte
102 Either compressed or uncompressed protocol fields
103 are accepted on incoming frames.
104 Similarly, if address and control
105 field compression has been enabled for the link, the address and
106 control fields will be omitted (except for LCP frames as required
108 Incoming frames have the address and control fields
109 stripped automatically if present.
111 Since all negotiation is handled outside the PPP node, the links
112 should not be connected and enabled until the corresponding link
113 has reached the network phase (i.e., LCP negotiation and authentication
114 have completed successfully) and the PPP node has been informed of
115 the link parameters via the
116 .Dv NGM_PPP_LINK_CONFIG
119 When a link is connected but disabled, all received frames are forwarded
122 hook, and conversely, frames may be transmitted via the
125 This mode is appropriate for the link authentication phase.
126 As soon as the link is enabled, the PPP node will
127 begin processing frames received on the link.
128 .Sh COMPRESSION AND ENCRYPTION
129 Compression is supported via two hooks,
133 When enabled and connected, the PPP node writes outgoing frames on the
135 hook and expects to receive back the compressed frame on the same hook.
138 hook is used to uncompress incoming frames when decompression is
139 negotiated (compression and decompression are independently negotiable).
140 The type of node attached to these hooks should correspond
141 to the type of compression negotiated, e.g., Deflate, Predictor-1, etc.
143 Encryption works exactly analogously via the
148 Data is always compressed before being encrypted,
149 and decrypted before being decompressed.
151 Only bundle-level compression and encryption is directly supported;
152 link-level compression and encryption can be handled transparently
154 .Sh VAN JACOBSON COMPRESSION
161 hooks are connected, and the corresponding configuration flag is
162 enabled, Van Jacobson compression and/or decompression will become active.
163 Normally these hooks connect to the corresponding hooks of a single
165 node. The PPP node is compatible with the
171 When a frame is received on a link with an unsupported protocol,
172 or a protocol which is disabled or for which the corresponding hook
173 is unconnected, the PPP node forwards the frame out the
175 hook, prepended with a four byte prefix.
176 This first two bytes of
177 the prefix indicate the link number on which the frame was received
179 For such frames received over the bundle (i.e., encapsulated in the
180 multi-link protocol), the special link number
181 .Dv NG_PPP_BUNDLE_LINKNUM
182 is used. After the two byte link number is the two byte PPP protocol number
183 (also in network order).
184 The PPP protocol number is two bytes long even if the original frame
185 was protocol compressed.
187 Conversely, any data written to the
189 hook is assumed to be in this same format.
190 The four byte header is
191 stripped off, the PPP protocol number is prepended (possibly compressed),
192 and the frame is delivered over the desired link.
193 If the link number is
194 .Dv NG_PPP_BUNDLE_LINKNUM
195 the frame will be delivered over the multi-link bundle; or, if multi-link
196 is disabled, over the (single) PPP link.
198 Typically when the controlling entity receives an unexpected packet on the
200 hook it responds either by dropping the frame (if it's not ready for
201 the protocol) or with an LCP protocol reject (if it doesn't recognize
202 or expect the protocol).
203 .Sh MULTILINK OPERATION
204 To enable multi-link PPP, the corresponding configuration flag must be set
205 and at least one link connected.
206 The PPP node will not allow more than
207 one link to be connected if multi-link is not enabled, nor will it allow
208 certain multi-link settings to be changed while multi-link operation is
209 active (e.g., short sequence number header format).
211 Since packets are sent as fragments across multiple individual links,
212 it is important that when a link goes down the PPP node is notified
213 immediately, either by disconnecting the corresponding hook or disabling
215 .Dv NGM_PPP_SET_CONFIG
218 Each link has configuration parameters for latency (specified in
219 milliseconds) and bandwidth (specified in tens of bytes per second).
220 The PPP node can be configured for
226 When configured for round-robin delivery, the latency and bandwidth
227 values are ignored and the PPP node simply sends each frame as a
228 single fragment, alternating frames across all the links in the
230 This scheme has the advantage that even if one link fails
231 silently, some packets will still get through.
232 It has the disadvantage
233 of sub-optimal overall bundle latency, which is important for
234 interactive response time, and sub-optimal overall bundle bandwidth
235 when links with different bandwidths exist in the same bundle.
237 When configured for optimal delivery, the PPP node distributes the
238 packet across the links in a way that minimizes the time it takes
239 for the completed packet to be received by the far end.
240 This involves taking into account each link's latency, bandwidth, and
241 current queue length.
242 Therefore these numbers should be configured as accurately as possible.
243 The algorithm does require
244 some computation, so may not be appropriate for very slow machines
245 and/or very fast links.
247 As a special case, if all links have identical latency and bandwidth,
248 then the above algorithm is disabled (because it is unnecessary)
249 and the PPP node simply fragments frames into equal sized portions
250 across all of the links.
252 This node type supports the following hooks:
254 .Bl -tag -compact -width vjc_vjuncomp
256 Individual PPP link number
259 Connection to compression engine
261 Connection to decompression engine
263 Connection to encryption engine
265 Connection to decryption engine
289 AppleTalk packet data
293 Bypass hook; frames have a four byte header consisting of
294 a link number and a PPP protocol number.
297 This node type supports the generic control messages, plus the following:
299 .It Dv NGM_PPP_SET_CONFIG
300 This command configures all aspects of the node.
301 This includes enabling
302 multi-link PPP, encryption, compression, Van Jacobson compression, and IP,
303 AppleTalk, and IPX packet delivery.
304 It includes per-link configuration,
305 including enabling the link, setting latency and bandwidth parameters,
306 and enabling protocol field compression.
307 Note that no link or functionality
308 is active until the corresponding hook is also connected.
310 .Dv "struct ng_ppp_node_config"
312 .Bd -literal -offset 0n
313 /* Per-link config structure */
314 struct ng_ppp_link_config {
315 u_char enableLink; /* enable this link */
316 u_char enableProtoComp;/* enable protocol field compression */
317 u_char enableACFComp; /* enable addr/ctrl field compression */
318 u_int16_t mru; /* peer MRU */
319 u_int32_t latency; /* link latency (in milliseconds) */
320 u_int32_t bandwidth; /* link bandwidth (in bytes/second) */
323 /* Node config structure */
324 struct ng_ppp_node_config {
325 u_int16_t mrru; /* multilink peer MRRU */
326 u_char enableMultilink; /* enable multilink */
327 u_char recvShortSeq; /* recv multilink short seq # */
328 u_char xmitShortSeq; /* xmit multilink short seq # */
329 u_char enableRoundRobin; /* xmit whole packets */
330 u_char enableIP; /* enable IP data flow */
331 u_char enableAtalk; /* enable AppleTalk data flow */
332 u_char enableIPX; /* enable IPX data flow */
333 u_char enableCompression; /* enable PPP compression */
334 u_char enableDecompression; /* enable PPP decompression */
335 u_char enableEncryption; /* enable PPP encryption */
336 u_char enableDecryption; /* enable PPP decryption */
337 u_char enableVJCompression; /* enable VJ compression */
338 u_char enableVJDecompression; /* enable VJ decompression */
339 struct ng_ppp_link_config /* per link config params */
340 links[NG_PPP_MAX_LINKS];
344 .It Dv NGM_PPP_GET_CONFIG
345 Returns the current configuration as a
346 .Dv "struct ng_ppp_node_config" .
347 .It Dv NGM_PPP_GET_LINK_STATS
348 This command takes a two byte link number as an argument and returns a
349 .Dv "struct ng_ppp_link_stat"
350 containing statistics for the corresponding link. Here
351 .Dv NG_PPP_BUNDLE_LINKNUM
352 is a valid link number corresponding to the multi-link bundle.
353 .It Dv NGM_PPP_CLR_LINK_STATS
354 This command takes a two byte link number as an argument and
355 clears the statistics for that link.
356 .It Dv NGM_PPP_GETCLR_LINK_STATS
358 .Dv NGM_PPP_GET_LINK_STATS ,
359 but also atomically clears the statistics as well.
362 This node type also accepts the control messages accepted by the
364 node type. When received, these messages are simply forwarded to
367 node, if any. This is particularly useful when the individual
368 PPP links are able to generate
369 .Dv NGM_VJC_RECV_ERROR
374 This node shuts down upon receipt of a
376 control message, or when all hooks have been disconnected.
387 .%T "The Point-to-Point Protocol (PPP)"
396 .%T "The PPP Multilink Protocol (MP)"
402 node type was implemented in
405 .An Archie Cobbs Aq archie@FreeBSD.org