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33 .\" Author: Archie Cobbs <archie@FreeBSD.org>
35 .\" $FreeBSD: src/share/man/man4/ng_ppp.4,v 1.18.2.1 2001/12/21 09:00:51 ru Exp $
36 .\" $DragonFly: src/share/man/man4/ng_ppp.4,v 1.3 2006/05/26 21:39:39 swildner Exp $
37 .\" $Whistle: ng_ppp.8,v 1.3 1999/01/25 23:46:27 archie Exp $
44 .Nd PPP protocol netgraph node type
46 .In netgraph/ppp/ng_ppp.h
50 node type performs multiplexing for the PPP protocol. It handles
51 only packets that contain data, and forwards protocol negotiation
52 and control packets to a separate controlling entity (e.g., a
53 user-land daemon). This approach combines the fast dispatch of
54 kernel implementations with the configuration flexibility of a
55 user-land implementations. The PPP node type directly supports
56 multi-link PPP, Van Jacobson compression, PPP compression, PPP
57 encryption, and the IP, IPX, and AppleTalk protocols. A single
58 PPP node corresponds to one PPP multi-link bundle.
60 There is a separate hook for each PPP link in the bundle, plus
61 several hooks corresponding to the directly supported protocols.
62 For compression and encryption, separate attached nodes are required
63 to do the actual work. The node type used will of course depend
64 on the algorithm negotiated. There is also a
66 hook which is used to handle any protocol not directly supported
67 by the node. This includes all of the control protocols: LCP, IPCP,
68 CCP, etc. Typically this node is connected to a user-land daemon
72 .Sh ENABLING FUNCTIONALITY
73 In general, the PPP node enables a specific link or functionality when
75 .Dv NGM_PPP_SET_CONFIG
76 message has been received which enables it, and
77 (b) the corresponding hook(s) are connected.
78 This allows the controlling entity to use either method (a) or (b)
79 (or both) to control the node's behavior.
80 When a link is connected but disabled, traffic can still flow on
85 During normal operation, the individual PPP links are connected to hooks
91 These device-independent hooks transmit and receive full PPP
92 frames, which include the PPP protocol, address, control, and
93 information fields, but no checksum or other link-specific fields.
95 On outgoing frames, when protocol compression
96 has been enabled and the protocol number is suitable for compression,
97 the protocol field will be compressed (i.e., sent as one byte
98 instead of two). Either compressed or uncompressed protocol fields
99 are accepted on incoming frames. Similarly, if address and control
100 field compression has been enabled for the link, the address and
101 control fields will be omitted (except for LCP frames as required
102 by the standards). Incoming frames have the address and control fields
103 stripped automatically if present.
105 Since all negotiation is handled outside the PPP node, the links
106 should not be connected and enabled until the corresponding link
107 has reached the network phase (i.e., LCP negotiation and authentication
108 have completed successfully) and the PPP node has been informed of
109 the link parameters via the
110 .Dv NGM_PPP_LINK_CONFIG
113 When a link is connected but disabled, all received frames are forwarded
116 hook, and conversely, frames may be transmitted via the
118 hook as well. This mode is appropriate for the link authentication phase.
119 As soon as the link is enabled, the PPP node will
120 begin processing frames received on the link.
121 .Sh COMPRESSION AND ENCRYPTION
122 Compression is supported via two hooks,
126 When enabled and connected, the PPP node writes outgoing frames on the
128 hook and expects to receive back the compressed frame on the same hook.
131 hook is used to uncompress incoming frames when decompression is
132 negotiated (compression and decompression are independently negotiable).
133 The type of node attached to these hooks should correspond
134 to the type of compression negotiated, e.g., Deflate, Predictor-1, etc.
136 Encryption works exactly analogously via the
140 nodes. Data is always compressed before being encrypted,
141 and decrypted before being decompressed.
143 Only bundle-level compression and encryption is directly supported;
144 link-level compression and encryption can be handled transparently
146 .Sh VAN JACOBSON COMPRESSION
153 hooks are connected, and the corresponding configuration flag is
154 enabled, Van Jacobson compression and/or decompression will become active.
155 Normally these hooks connect to the corresponding hooks of a single
157 node. The PPP node is compatible with the
163 When a frame is received on a link with an unsupported protocol,
164 or a protocol which is disabled or for which the corresponding hook
165 is unconnected, the PPP node forwards the frame out the
167 hook, prepended with a four byte prefix. This first two bytes of
168 the prefix indicate the link number on which the frame was received
170 For such frames received over the bundle (i.e., encapsulated in the
171 multi-link protocol), the special link number
172 .Dv NG_PPP_BUNDLE_LINKNUM
173 is used. After the two byte link number is the two byte PPP protocol number
174 (also in network order).
175 The PPP protocol number is two bytes long even if the original frame
176 was protocol compressed.
178 Conversely, any data written to the
180 hook is assumed to be in this same format. The four byte header is
181 stripped off, the PPP protocol number is prepended (possibly compressed),
182 and the frame is delivered over the desired link.
183 If the link number is
184 .Dv NG_PPP_BUNDLE_LINKNUM
185 the frame will be delivered over the multi-link bundle; or, if multi-link
186 is disabled, over the (single) PPP link.
188 Typically when the controlling entity receives an unexpected packet on the
190 hook it responds either by dropping the frame (if it's not ready for
191 the protocol) or with an LCP protocol reject (if it doesn't recognize
192 or expect the protocol).
193 .Sh MULTILINK OPERATION
194 To enable multi-link PPP, the corresponding configuration flag must be set
195 and at least one link connected. The PPP node will not allow more than
196 one link to be connected if multi-link is not enabled, nor will it allow
197 certain multi-link settings to be changed while multi-link operation is
198 active (e.g., short sequence number header format).
200 Because packets are sent as fragments across multiple individual links,
201 it is important that when a link goes down the PPP node is notified
202 immediately, either by disconnecting the corresponding hook or disabling
204 .Dv NGM_PPP_SET_CONFIG
207 Each link has configuration parameters for latency (specified in
208 milliseconds) and bandwidth (specified in tens of bytes per second).
209 The PPP node can be configured for
215 When configured for round-robin delivery, the latency and bandwidth
216 values are ignored and the PPP node simply sends each frame as a
217 single fragment, alternating frames across all the links in the
218 bundle. This scheme has the advantage that even if one link fails
219 silently, some packets will still get through. It has the disadvantage
220 of sub-optimal overall bundle latency, which is important for
221 interactive response time, and sub-optimal overall bundle bandwidth
222 when links with different bandwidths exist in the same bundle.
224 When configured for optimal delivery, the PPP node distributes the
225 packet across the links in a way that minimizes the time it takes
226 for the completed packet to be received by the far end. This
227 involves taking into account each link's latency, bandwidth, and
228 current queue length. Therefore these numbers should be
229 configured as accurately as possible. The algorithm does require
230 some computation, so may not be appropriate for very slow machines
231 and/or very fast links.
233 As a special case, if all links have identical latency and bandwidth,
234 then the above algorithm is disabled (because it is unnecessary)
235 and the PPP node simply fragments frames into equal sized portions
236 across all of the links.
238 This node type supports the following hooks:
240 .Bl -tag -compact -width vjc_vjuncomp
242 Individual PPP link number
245 Connection to compression engine
247 Connection to decompression engine
249 Connection to encryption engine
251 Connection to decryption engine
275 AppleTalk packet data
279 Bypass hook; frames have a four byte header consisting of
280 a link number and a PPP protocol number.
283 This node type supports the generic control messages, plus the following:
285 .It Dv NGM_PPP_SET_CONFIG
286 This command configures all aspects of the node. This includes enabling
287 multi-link PPP, encryption, compression, Van Jacobson compression, and IP,
288 AppleTalk, and IPX packet delivery. It includes per-link configuration,
289 including enabling the link, setting latency and bandwidth parameters,
290 and enabling protocol field compression. Note that no link or functionality
291 is active until the corresponding hook is also connected.
293 .Dv "struct ng_ppp_node_config"
295 .Bd -literal -offset 0n
296 /* Per-link config structure */
297 struct ng_ppp_link_config {
298 u_char enableLink; /* enable this link */
299 u_char enableProtoComp;/* enable protocol field compression */
300 u_char enableACFComp; /* enable addr/ctrl field compression */
301 u_int16_t mru; /* peer MRU */
302 u_int32_t latency; /* link latency (in milliseconds) */
303 u_int32_t bandwidth; /* link bandwidth (in bytes/second) */
306 /* Node config structure */
307 struct ng_ppp_node_config {
308 u_int16_t mrru; /* multilink peer MRRU */
309 u_char enableMultilink; /* enable multilink */
310 u_char recvShortSeq; /* recv multilink short seq # */
311 u_char xmitShortSeq; /* xmit multilink short seq # */
312 u_char enableRoundRobin; /* xmit whole packets */
313 u_char enableIP; /* enable IP data flow */
314 u_char enableAtalk; /* enable AppleTalk data flow */
315 u_char enableIPX; /* enable IPX data flow */
316 u_char enableCompression; /* enable PPP compression */
317 u_char enableDecompression; /* enable PPP decompression */
318 u_char enableEncryption; /* enable PPP encryption */
319 u_char enableDecryption; /* enable PPP decryption */
320 u_char enableVJCompression; /* enable VJ compression */
321 u_char enableVJDecompression; /* enable VJ decompression */
322 struct ng_ppp_link_config /* per link config params */
323 links[NG_PPP_MAX_LINKS];
327 .It Dv NGM_PPP_GET_CONFIG
328 Returns the current configuration as a
329 .Dv "struct ng_ppp_node_config" .
330 .It Dv NGM_PPP_GET_LINK_STATS
331 This command takes a two byte link number as an argument and returns a
332 .Dv "struct ng_ppp_link_stat"
333 containing statistics for the corresponding link. Here
334 .Dv NG_PPP_BUNDLE_LINKNUM
335 is a valid link number corresponding to the multi-link bundle.
336 .It Dv NGM_PPP_CLR_LINK_STATS
337 This command takes a two byte link number as an argument and
338 clears the statistics for that link.
339 .It Dv NGM_PPP_GETCLR_LINK_STATS
341 .Dv NGM_PPP_GET_LINK_STATS ,
342 but also atomically clears the statistics as well.
345 This node type also accepts the control messages accepted by the
347 node type. When received, these messages are simply forwarded to
350 node, if any. This is particularly useful when the individual
351 PPP links are able to generate
352 .Dv NGM_VJC_RECV_ERROR
357 This node shuts down upon receipt of a
359 control message, or when all hooks have been disconnected.
370 .%T "The Point-to-Point Protocol (PPP)"
379 .%T "The PPP Multilink Protocol (MP)"
385 node type was implemented in
388 .An Archie Cobbs Aq archie@FreeBSD.org