1 .\" manual page [] for pppd 2.3
2 .\" $Id: pppd.8,v 1.31 1999/02/26 10:38:52 paulus Exp $
4 .\" SS subsection heading
6 .\" IP indented paragraph
10 pppd \- Point to Point Protocol daemon
22 The Point-to-Point Protocol (PPP) provides a method for transmitting
23 datagrams over serial point-to-point links. PPP
24 is composed of three parts: a method for encapsulating datagrams over
25 serial links, an extensible Link Control Protocol (LCP), and
26 a family of Network Control Protocols (NCP) for establishing
27 and configuring different network-layer protocols.
29 The encapsulation scheme is provided by driver code in the kernel.
30 Pppd provides the basic LCP, authentication support, and an NCP for
31 establishing and configuring the Internet Protocol (IP) (called the IP
32 Control Protocol, IPCP).
33 .SH FREQUENTLY USED OPTIONS
36 Communicate over the named device. The string "/dev/" is prepended if
37 necessary. If no device name is given, or if the name of the terminal
38 connected to the standard input is given, pppd
39 will use that terminal, and will not fork to put itself in the
40 background. This option is privileged if the \fInoauth\fR option is
44 Set the baud rate to <speed> (a decimal number). On systems such as
45 4.4BSD and NetBSD, any speed can be specified. Other systems
46 (e.g. SunOS) allow only a limited set of speeds.
48 .B active-filter \fIfilter-expression
49 Specifies a packet filter to be applied to data packets to determine
50 which packets are to be regarded as link activity, and therefore reset
51 the idle timer, or cause the link to be brought up in demand-dialling
52 mode. This option is useful in conjunction with the
53 \fBidle\fR option if there are packets being sent or received
54 regularly over the link (for example, routing information packets)
55 which would otherwise prevent the link from ever appearing to be idle.
56 The \fIfilter-expression\fR syntax is as described for tcpdump(1),
57 except that qualifiers which are inappropriate for a PPP link, such as
58 \fBether\fR and \fBarp\fR, are not permitted. Generally the filter
59 expression should be enclosed in single-quotes to prevent whitespace
60 in the expression from being interpreted by the shell. This option
61 is currently only available under NetBSD, and then only
62 if both the kernel and pppd were compiled with PPP_FILTER defined.
65 Set the async character map to <map>. This map describes which
66 control characters cannot be successfully received over the serial
67 line. Pppd will ask the peer to send these characters as a 2-byte
68 escape sequence. The argument is a 32 bit hex number with each bit
69 representing a character to escape. Bit 0 (00000001) represents the
70 character 0x00; bit 31 (80000000) represents the character 0x1f or ^_.
71 If multiple \fIasyncmap\fR options are given, the values are ORed
72 together. If no \fIasyncmap\fR option is given, no async character
73 map will be negotiated for the receive direction; the peer should then
74 escape \fIall\fR control characters. To escape transmitted
75 characters, use the \fIescape\fR option.
78 Require the peer to authenticate itself before allowing network
79 packets to be sent or received. If neither this option nor the
80 \fInoauth\fR option is specified, the default is that pppd will not
81 require the peer to authenticate, but will then only allow it to use
82 IP addresses to which the system does not already have a route.
85 Read options from the file /etc/ppp/peers/\fIname\fR. This file may
86 contain privileged options, such as \fInoauth\fR, even if pppd
87 is not being run by root. The \fIname\fR string may not begin with /
88 or include .. as a pathname component. The format of the options file
92 Use the executable or shell command specified by \fIscript\fR to set
93 up the serial line. This script would typically use the chat(8)
94 program to dial the modem and start the remote ppp session. This
95 option is privileged if the \fInoauth\fR option is used.
98 Use hardware flow control (i.e. RTS/CTS) to control the flow of
99 data on the serial port. If neither the \fIcrtscts\fR, the
100 \fInocrtscts\fR, the \fIcdtrcts\fR nor the \fInocdtrcts\fR option
101 is given, the hardware flow control setting for the serial port is
103 Some serial ports (such as Macintosh serial ports) lack a true
104 RTS output. Such serial ports use this mode to implement
105 unidirectional flow control. The serial port will
106 suspend transmission when requested by the modem (via CTS)
107 but will be unable to request the modem stop sending to the
108 computer. This mode retains the ability to use DTR as
109 a modem control line.
112 Use a non-standard hardware flow control (i.e. DTR/CTS) to control
113 the flow of data on the serial port. If neither the \fIcrtscts\fR,
114 the \fInocrtscts\fR, the \fIcdtrcts\fR nor the \fInocdtrcts\fR
115 option is given, the hardware flow control setting for the serial
116 port is left unchanged.
117 Some serial ports (such as Macintosh serial ports) lack a true
118 RTS output. Such serial ports use this mode to implement true
119 bi-directional flow control. The sacrifice is that this flow
120 control mode does not permit using DTR as a modem control line.
123 Add a default route to the system routing tables, using the peer as
124 the gateway, when IPCP negotiation is successfully completed.
125 This entry is removed when the PPP connection is broken. This option
126 is privileged if the \fInodefaultroute\fR option has been specified.
128 .B disconnect \fIscript
129 Run the executable or shell command specified by \fIscript\fR after
130 pppd has terminated the link. This script could, for example, issue
131 commands to the modem to cause it to hang up if hardware modem control
132 signals were not available. The disconnect script is not run if the
133 modem has already hung up. This option is privileged if the
134 \fInoauth\fR option is used.
136 .B escape \fIxx,yy,...
137 Specifies that certain characters should be escaped on transmission
138 (regardless of whether the peer requests them to be escaped with its
139 async control character map). The characters to be escaped are
140 specified as a list of hex numbers separated by commas. Note that
141 almost any character can be specified for the \fIescape\fR option,
142 unlike the \fIasyncmap\fR option which only allows control characters
143 to be specified. The characters which may not be escaped are those
144 with hex values 0x20 - 0x3f or 0x5e.
147 Read options from file \fIname\fR (the format is described below).
148 The file must be readable by the user who has invoked pppd.
151 Specifies that pppd should create a UUCP-style lock file for the
152 serial device to ensure exclusive access to the device.
155 Set the MRU [Maximum Receive Unit] value to \fIn\fR. Pppd
156 will ask the peer to send packets of no more than \fIn\fR bytes. The
157 minimum MRU value is 128. The default MRU value is 1500. A value of
158 296 is recommended for slow links (40 bytes for TCP/IP header + 256
162 Set the MTU [Maximum Transmit Unit] value to \fIn\fR. Unless the
163 peer requests a smaller value via MRU negotiation, pppd will
164 request that the kernel networking code send data packets of no more
165 than \fIn\fR bytes through the PPP network interface.
168 Enables the "passive" option in the LCP. With this option, pppd will
169 attempt to initiate a connection; if no reply is received from the
170 peer, pppd will then just wait passively for a valid LCP packet from
171 the peer, instead of exiting, as it would without this option.
174 .I <local_IP_address>\fB:\fI<remote_IP_address>
175 Set the local and/or remote interface IP addresses. Either one may be
176 omitted. The IP addresses can be specified with a host name or in
177 decimal dot notation (e.g. 150.234.56.78). The default local
178 address is the (first) IP address of the system (unless the
180 option is given). The remote address will be obtained from the peer
181 if not specified in any option. Thus, in simple cases, this option is
182 not required. If a local and/or remote IP address is specified with
184 will not accept a different value from the peer in the IPCP
185 negotiation, unless the \fIipcp-accept-local\fR and/or
186 \fIipcp-accept-remote\fR options are given, respectively.
189 Request that the peer compress packets that it sends, using the
190 BSD-Compress scheme, with a maximum code size of \fInr\fR bits, and
191 agree to compress packets sent to the peer with a maximum code size of
192 \fInt\fR bits. If \fInt\fR is not specified, it defaults to the value
193 given for \fInr\fR. Values in the range 9 to 15 may be used for
194 \fInr\fR and \fInt\fR; larger values give better compression but
195 consume more kernel memory for compression dictionaries.
196 Alternatively, a value of 0 for \fInr\fR or \fInt\fR disables
197 compression in the corresponding direction. Use \fInobsdcomp\fR or
198 \fIbsdcomp 0\fR to disable BSD-Compress compression entirely.
200 .B chap-interval \fIn
201 If this option is given, pppd will rechallenge the peer every \fIn\fR
204 .B chap-max-challenge \fIn
205 Set the maximum number of CHAP challenge transmissions to \fIn\fR
209 Set the CHAP restart interval (retransmission timeout for challenges)
210 to \fIn\fR seconds (default 3).
213 Enables connection debugging facilities.
214 If this option is given, pppd will log the contents of all
215 control packets sent or received in a readable form. The packets are
216 logged through syslog with facility \fIdaemon\fR and level
217 \fIdebug\fR. This information can be directed to a file by setting up
218 /etc/syslog.conf appropriately (see syslog.conf(5)).
221 Disable asyncmap negotiation, forcing all control characters to be
222 escaped for both the transmit and the receive direction.
225 Disable MRU [Maximum Receive Unit] negotiation. With this option,
226 pppd will use the default MRU value of 1500 bytes for both the
227 transmit and receive direction.
230 Request that the peer compress packets that it sends, using the
231 Deflate scheme, with a maximum window size of \fI2**nr\fR bytes, and
232 agree to compress packets sent to the peer with a maximum window size
233 of \fI2**nt\fR bytes. If \fInt\fR is not specified, it defaults to
234 the value given for \fInr\fR. Values in the range 8 to 15 may be used
235 for \fInr\fR and \fInt\fR; larger values give better compression but
236 consume more kernel memory for compression dictionaries.
237 Alternatively, a value of 0 for \fInr\fR or \fInt\fR disables
238 compression in the corresponding direction. Use \fInodeflate\fR or
239 \fIdeflate 0\fR to disable Deflate compression entirely. (Note: pppd
240 requests Deflate compression in preference to BSD-Compress if the peer
244 Initiate the link only on demand, i.e. when data traffic is present.
245 With this option, the remote IP address must be specified by the user
246 on the command line or in an options file. Pppd will initially
247 configure the interface and enable it for IP traffic without
248 connecting to the peer. When traffic is available, pppd will
249 connect to the peer and perform negotiation, authentication, etc.
250 When this is completed, pppd will commence passing data packets
251 (i.e., IP packets) across the link.
253 The \fIdemand\fR option implies the \fIpersist\fR option. If this
254 behaviour is not desired, use the \fInopersist\fR option after the
255 \fIdemand\fR option. The \fIidle\fR and \fIholdoff\fR
256 options are also useful in conjuction with the \fIdemand\fR option.
259 Append the domain name \fId\fR to the local host name for authentication
260 purposes. For example, if gethostname() returns the name porsche, but
261 the fully qualified domain name is porsche.Quotron.COM, you could
262 specify \fIdomain Quotron.COM\fR. Pppd would then use the name
263 \fIporsche.Quotron.COM\fR for looking up secrets in the secrets file,
264 and as the default name to send to the peer when authenticating itself
265 to the peer. This option is privileged.
268 Specifies how many seconds to wait before re-initiating the link after
269 it terminates. This option only has any effect if the \fIpersist\fR
270 or \fIdemand\fR option is used. The holdoff period is not applied if
271 the link was terminated because it was idle.
274 Specifies that pppd should disconnect if the link is idle for \fIn\fR
275 seconds. The link is idle when no data packets (i.e. IP packets) are
276 being sent or received. Note: it is not advisable to use this option
277 with the \fIpersist\fR option without the \fIdemand\fR option.
278 If the \fBactive-filter\fR
279 option is given, data packets which are rejected by the specified
280 activity filter also count as the link being idle.
283 With this option, pppd will accept the peer's idea of our local IP
284 address, even if the local IP address was specified in an option.
286 .B ipcp-accept-remote
287 With this option, pppd will accept the peer's idea of its (remote) IP
288 address, even if the remote IP address was specified in an option.
290 .B ipcp-max-configure \fIn
291 Set the maximum number of IPCP configure-request transmissions to
292 \fIn\fR (default 10).
294 .B ipcp-max-failure \fIn
295 Set the maximum number of IPCP configure-NAKs returned before starting
296 to send configure-Rejects instead to \fIn\fR (default 10).
298 .B ipcp-max-terminate \fIn
299 Set the maximum number of IPCP terminate-request transmissions to
303 Set the IPCP restart interval (retransmission timeout) to \fIn\fR
307 Provides an extra parameter to the ip-up and ip-down scripts. If this
308 option is given, the \fIstring\fR supplied is given as the 6th
309 parameter to those scripts.
312 Enable the IPXCP and IPX protocols. This option is presently only
313 supported under Linux, and only if your kernel has been configured to
317 Set the IPX network number in the IPXCP configure request frame to
318 \fIn\fR, a hexadecimal number (without a leading 0x). There is no
319 valid default. If this option is not specified, the network number is
320 obtained from the peer. If the peer does not have the network number,
321 the IPX protocol will not be started.
323 .B ipx-node \fIn\fB:\fIm
324 Set the IPX node numbers. The two node numbers are separated from each
325 other with a colon character. The first number \fIn\fR is the local
326 node number. The second number \fIm\fR is the peer's node number. Each
327 node number is a hexadecimal number, at most 10 digits long. The node
328 numbers on the ipx-network must be unique. There is no valid
329 default. If this option is not specified then the node numbers are
330 obtained from the peer.
332 .B ipx-router-name \fI<string>
333 Set the name of the router. This is a string and is sent to the peer
337 Set the routing protocol to be received by this option. More than one
338 instance of \fIipx-routing\fR may be specified. The '\fInone\fR'
339 option (0) may be specified as the only instance of ipx-routing. The
340 values may be \fI0\fR for \fINONE\fR, \fI2\fR for \fIRIP/SAP\fR, and
341 \fI4\fR for \fINLSP\fR.
343 .B ipxcp-accept-local
344 Accept the peer's NAK for the node number specified in the ipx-node
345 option. If a node number was specified, and non-zero, the default is
346 to insist that the value be used. If you include this option then you
347 will permit the peer to override the entry of the node number.
349 .B ipxcp-accept-network
350 Accept the peer's NAK for the network number specified in the
351 ipx-network option. If a network number was specified, and non-zero, the
352 default is to insist that the value be used. If you include this
353 option then you will permit the peer to override the entry of the node
356 .B ipxcp-accept-remote
357 Use the peer's network number specified in the configure request
358 frame. If a node number was specified for the peer and this option was
359 not specified, the peer will be forced to use the value which you have
362 .B ipxcp-max-configure \fIn
363 Set the maximum number of IPXCP configure request frames which the
364 system will send to \fIn\fR. The default is 10.
366 .B ipxcp-max-failure \fIn
367 Set the maximum number of IPXCP NAK frames which the local system will
368 send before it rejects the options. The default value is 3.
370 .B ipxcp-max-terminate \fIn
371 Set the maximum nuber of IPXCP terminate request frames before the
372 local system considers that the peer is not listening to them. The
376 Enable debugging code in the kernel-level PPP driver. The argument
377 \fIn\fR is a number which is the sum of the following values: 1 to
378 enable general debug messages, 2 to request that the contents of
379 received packets be printed, and 4 to request that the contents of
380 transmitted packets be printed. On most systems, messages printed by
381 the kernel are logged by syslog(1) to a file as directed in the
382 /etc/syslog.conf configuration file.
384 .B lcp-echo-failure \fIn
385 If this option is given, pppd will presume the peer to be dead
386 if \fIn\fR LCP echo-requests are sent without receiving a valid LCP
387 echo-reply. If this happens, pppd will terminate the
388 connection. Use of this option requires a non-zero value for the
389 \fIlcp-echo-interval\fR parameter. This option can be used to enable
390 pppd to terminate after the physical connection has been broken
391 (e.g., the modem has hung up) in situations where no hardware modem
392 control lines are available.
394 .B lcp-echo-interval \fIn
395 If this option is given, pppd will send an LCP echo-request frame to
396 the peer every \fIn\fR seconds. Normally the peer should respond to
397 the echo-request by sending an echo-reply. This option can be used
398 with the \fIlcp-echo-failure\fR option to detect that the peer is no
401 .B lcp-max-configure \fIn
402 Set the maximum number of LCP configure-request transmissions to
403 \fIn\fR (default 10).
405 .B lcp-max-failure \fIn
406 Set the maximum number of LCP configure-NAKs returned before starting
407 to send configure-Rejects instead to \fIn\fR (default 10).
409 .B lcp-max-terminate \fIn
410 Set the maximum number of LCP terminate-request transmissions to
414 Set the LCP restart interval (retransmission timeout) to \fIn\fR
418 Don't use the modem control lines. With this option, pppd will ignore
419 the state of the CD (Carrier Detect) signal from the modem and will
420 not change the state of the DTR (Data Terminal Ready) signal.
423 Use the system password database for authenticating the peer using
424 PAP, and record the user in the system wtmp file. Note that the peer
425 must have an entry in the /etc/ppp/pap-secrets file as well as the
426 system password database to be allowed access.
429 Terminate the connection when it has been available for network
430 traffic for \fIn\fR seconds (i.e. \fIn\fR seconds after the first
431 network control protocol comes up).
434 Use the modem control lines. This option is the default. With this
435 option, pppd will wait for the CD (Carrier Detect) signal from the
436 modem to be asserted when opening the serial device (unless a connect
437 script is specified), and it will drop the DTR (Data Terminal Ready)
438 signal briefly when the connection is terminated and before executing
439 the connect script. On Ultrix, this option implies hardware flow
440 control, as for the \fIcrtscts\fR option.
443 If pppd is acting as a server for Microsoft Windows clients, this
444 option allows pppd to supply one or two DNS (Domain Name Server)
445 addresses to the clients. The first instance of this option specifies
446 the primary DNS address; the second instance (if given) specifies the
447 secondary DNS address. (This option was present in some older
448 versions of pppd under the name \fBdns-addr\fR.)
451 If pppd is acting as a server for Microsoft Windows or "Samba"
452 clients, this option allows pppd to supply one or two WINS (Windows
453 Internet Name Services) server addresses to the clients. The first
454 instance of this option specifies the primary WINS address; the second
455 instance (if given) specifies the secondary WINS address.
458 Set the name of the local system for authentication purposes to
459 \fIname\fR. This is a privileged option. With this option, pppd will
460 use lines in the secrets files which have \fIname\fR as the second
461 field when looking for a secret to use in authenticating the peer. In
462 addition, unless overridden with the \fIuser\fR option, \fIname\fR
463 will be used as the name to send to the peer when authenticating the
464 local system to the peer. (Note that pppd does not append the domain
468 Set the interface netmask to \fIn\fR, a 32 bit netmask in "decimal dot"
469 notation (e.g. 255.255.255.0). If this option is given, the value
470 specified is ORed with the default netmask. The default netmask is
471 chosen based on the negotiated remote IP address; it is the
472 appropriate network mask for the class of the remote IP address, ORed
473 with the netmasks for any non point-to-point network interfaces in the
474 system which are on the same network. (Note: on some platforms, pppd
475 will always use 255.255.255.255 for the netmask, if that is the only
476 appropriate value for a point-to-point interface.)
479 Disable Address/Control compression in both directions (send and
483 Do not require the peer to authenticate itself. This option is
487 Disables BSD-Compress compression; \fBpppd\fR will not request or
488 agree to compress packets using the BSD-Compress scheme.
491 Disable CCP (Compression Control Protocol) negotiation. This option
492 should only be required if the peer is buggy and gets confused by
493 requests from pppd for CCP negotiation.
496 Disable hardware flow control (i.e. RTS/CTS) on the serial port.
497 If neither the \fIcrtscts\fR nor the \fInocrtscts\fR nor the
498 \fIcdtrcts\fR nor the \fInodtrcts\fR option is given, the hardware
499 flow control setting for the serial port is left unchanged.
502 This option is a synonym for \fInocrtscts\fR. Either of these options will
503 disable both forms of hardware flow control.
506 Disable the \fIdefaultroute\fR option. The system administrator who
507 wishes to prevent users from creating default routes with pppd
508 can do so by placing this option in the /etc/ppp/options file.
511 Disables Deflate compression; pppd will not request or agree to
512 compress packets using the Deflate scheme.
515 Don't detach from the controlling terminal. Without this option, if a
516 serial device other than the terminal on the standard input is
517 specified, pppd will fork to become a background process.
520 Disable IPCP negotiation and IP communication. This option should
521 only be required if the peer is buggy and gets confused by requests
522 from pppd for IPCP negotiation.
525 Disables the default behaviour when no local IP address is specified,
526 which is to determine (if possible) the local IP address from the
527 hostname. With this option, the peer will have to supply the local IP
528 address during IPCP negotiation (unless it specified explicitly on the
529 command line or in an options file).
532 Disable the IPXCP and IPX protocols. This option should only be
533 required if the peer is buggy and gets confused by requests from pppd
534 for IPXCP negotiation.
537 Disable magic number negotiation. With this option, pppd cannot
538 detect a looped-back line. This option should only be needed if the
542 Disable protocol field compression negotiation in both the receive and
543 the transmit direction.
546 Exit once a connection has been made and terminated. This is the
547 default unless the \fIpersist\fR or \fIdemand\fR option has been
551 Do not accept or agree to Predictor-1 comprssion.
554 Disable the \fIproxyarp\fR option. The system administrator who
555 wishes to prevent users from creating proxy ARP entries with pppd can
556 do so by placing this option in the /etc/ppp/options file.
559 Disable Van Jacobson style TCP/IP header compression in both the
560 transmit and the receive direction.
563 Disable the connection-ID compression option in Van Jacobson style
564 TCP/IP header compression. With this option, pppd will not omit the
565 connection-ID byte from Van Jacobson compressed TCP/IP headers, nor
566 ask the peer to do so.
569 Indicates that all secrets in the /etc/ppp/pap-secrets file which are
570 used for checking the identity of the peer are encrypted, and thus
571 pppd should not accept a password which, before encryption, is
572 identical to the secret from the /etc/ppp/pap-secrets file.
574 .B pap-max-authreq \fIn
575 Set the maximum number of PAP authenticate-request transmissions to
576 \fIn\fR (default 10).
579 Set the PAP restart interval (retransmission timeout) to \fIn\fR
583 Set the maximum time that pppd will wait for the peer to authenticate
584 itself with PAP to \fIn\fR seconds (0 means no limit).
586 .B pass-filter \fIfilter-expression
587 Specifies a packet filter to applied to data packets being sent or
588 received to determine which packets should be allowed to pass.
589 Packets which are rejected by the filter are silently discarded. This
590 option can be used to prevent specific network daemons (such as
591 routed) using up link bandwidth, or to provide a basic firewall
593 The \fIfilter-expression\fR syntax is as described for tcpdump(1),
594 except that qualifiers which are inappropriate for a PPP link, such as
595 \fBether\fR and \fBarp\fR, are not permitted. Generally the filter
596 expression should be enclosed in single-quotes to prevent whitespace
597 in the expression from being interpreted by the shell. Note that it
598 is possible to apply different constraints to incoming and outgoing
599 packets using the \fBinbound\fR and \fBoutbound\fR qualifiers. This
600 option is currently only available under NetBSD, and then only if both
601 the kernel and pppd were compiled with PPP_FILTER defined.
604 Do not exit after a connection is terminated; instead try to reopen
608 Request that the peer compress frames that it sends using Predictor-1
609 compression, and agree to compress transmitted frames with Predictor-1
610 if requested. This option has no effect unless the kernel driver
611 supports Predictor-1 compression.
614 Add an entry to this system's ARP [Address Resolution Protocol] table
615 with the IP address of the peer and the Ethernet address of this
616 system. This will have the effect of making the peer appear to other
617 systems to be on the local ethernet.
619 .B remotename \fIname
620 Set the assumed name of the remote system for authentication purposes
624 With this option, pppd will not agree to authenticate itself to the
628 With this option, pppd will not agree to authenticate itself to the
632 Require the peer to authenticate itself using CHAP [Challenge
633 Handshake Authentication Protocol] authentication.
636 Require the peer to authenticate itself using PAP [Password
637 Authentication Protocol] authentication.
640 With this option, pppd will not transmit LCP packets to initiate a
641 connection until a valid LCP packet is received from the peer (as for
642 the `passive' option with ancient versions of pppd).
645 Enforce the use of the hostname (with domain name appended, if given)
646 as the name of the local system for authentication purposes (overrides
647 the \fIname\fR option). This option is not normally needed since the
648 \fIname\fR option is privileged.
651 Sets the name used for authenticating the local system to the peer to
655 Sets the number of connection slots to be used by the Van Jacobson
656 TCP/IP header compression and decompression code to \fIn\fR, which
657 must be between 2 and 16 (inclusive).
660 Run the executable or shell command specified by \fIscript\fR before
661 initiating PPP negotiation, after the connect script (if any) has
662 completed. This option is privileged if the \fInoauth\fR option is
666 Use software flow control (i.e. XON/XOFF) to control the flow of data on
669 Options can be taken from files as well as the command line. Pppd
670 reads options from the files /etc/ppp/options, ~/.ppprc and
671 /etc/ppp/options.\fIttyname\fR (in that order) before processing the
672 options on the command line. (In fact, the command-line options are
673 scanned to find the terminal name before the options.\fIttyname\fR
674 file is read.) In forming the name of the options.\fIttyname\fR file,
675 the initial /dev/ is removed from the terminal name, and any remaining
676 / characters are replaced with dots.
678 An options file is parsed into a series of words, delimited by
679 whitespace. Whitespace can be included in a word by enclosing the
680 word in double-quotes ("). A backslash (\\) quotes the following character.
681 A hash (#) starts a comment, which continues until the end of the
682 line. There is no restriction on using the \fIfile\fR or \fIcall\fR
683 options within an options file.
686 provides system administrators with sufficient access control that PPP
687 access to a server machine can be provided to legitimate users without
688 fear of compromising the security of the server or the network it's
689 on. This control is provided through restrictions on which IP
690 addresses the peer may use, based on its authenticated identity (if
691 any), and through restrictions on which options a non-privileged user
692 may use. Several of pppd's options are privileged, in particular
693 those which permit potentially insecure configurations; these options
694 are only accepted in files which are under the control of the system
695 administrator, or if pppd is being run by root.
697 The default behaviour of pppd is to allow an unauthenticated peer
698 to use a given IP address if the system does not already have a
699 route to that IP address already. For example, a system with a
700 permanent connection to the wider internet will normally have a
701 default route, and thus all peers will have to authenticate themselves
702 in order to set up a connection. On such a system, the \fIauth\fR
703 option should be used in /etc/ppp/options so that pppd will ask the
704 peer to authenticate itself. On the other hand, a system where the
705 PPP link is the only connection to the internet will not normally have
706 a default route, so the peer will be able to use almost any IP address
707 without authenticating itself.
709 As indicated above, some security-sensitive options are privileged,
710 which means that they may not be used by an ordinary non-privileged
711 user running a setuid-root pppd, either on the command line, in the
712 user's ~/.ppprc file, or in an options file read using the \fIfile\fR
713 option. Privileged options may be used in /etc/ppp/options file or in
714 an options file read using the \fIcall\fR option. If pppd is being
715 run by the root user, privileged options can be used without
718 Authentication is the process whereby one peer convinces the other of
719 its identity. This involves the first peer sending its name to the
720 other, together with some kind of secret information which could only
721 come from the genuine authorized user of that name. In such an
722 exchange, we will call the first peer the "client" and the other the
723 "server". The client has a name by which it identifies itself to the
724 server, and the server also has a name by which it identifies itself
725 to the client. Generally the genuine client shares some secret (or
726 password) with the server, and authenticates itself by proving that it
727 knows that secret. Very often, the names used for authentication
728 correspond to the internet hostnames of the peers, but this is not
731 At present, pppd supports two authentication protocols: the Password
732 Authentication Protocol (PAP) and the Challenge Handshake
733 Authentication Protocol (CHAP). PAP involves the client sending its
734 name and a cleartext password to the server to authenticate itself.
735 In contrast, the server initiates the CHAP authentication exchange by
736 sending a challenge to the client (the challenge packet includes the
737 server's name). The client must respond with a response which
738 includes its name plus a hash value derived from the shared secret and
739 the challenge, in order to prove that it knows the secret.
741 The PPP protocol, being symmetrical, allows both peers to require the
742 other to authenticate itself. In that case, two separate and
743 independent authentication exchanges will occur. The two exchanges
744 could use different authentication protocols, and in principle,
745 different names could be used in the two exchanges.
747 The default behaviour of pppd is to agree to authenticate if
748 requested, and to not require authentication from the peer. However,
749 pppd will not agree to authenticate itself with a particular protocol
750 if it has no secrets which could be used to do so.
752 Pppd stores secrets for use in authentication in secrets
753 files (/etc/ppp/pap-secrets for PAP, /etc/ppp/chap-secrets for CHAP).
754 Both secrets files have the same format. The secrets files can
755 contain secrets for pppd to use in authenticating itself to other
756 systems, as well as secrets for pppd to use when authenticating other
759 Each line in a secrets file contains one secret. A given secret is
760 specific to a particular combination of client and server - it can
761 only be used by that client to authenticate itself to that server.
762 Thus each line in a secrets file has at least 3 fields: the name of
763 the client, the name of the server, and the secret. These fields may
764 be followed by a list of the IP addresses that the specified client
765 may use when connecting to the specified server.
767 A secrets file is parsed into words as for a options file, so the
768 client name, server name and secrets fields must each be one word,
769 with any embedded spaces or other special characters quoted or
770 escaped. Any following words on the same line are taken to be a list
771 of acceptable IP addresses for that client. If there are only 3 words
772 on the line, or if the first word is "-", then all IP addresses are
773 disallowed. To allow any address, use "*".
774 A word starting with "!" indicates that the
775 specified address is \fInot\fR acceptable. An address may be followed
776 by "/" and a number \fIn\fR, to indicate a whole subnet, i.e. all
777 addresses which have the same value in the most significant \fIn\fR
778 bits. Note that case is significant in the client and server names
781 If the secret starts with an `@', what follows is assumed to be the
782 name of a file from which to read the secret. A "*" as the client or
783 server name matches any name. When selecting a secret, pppd takes the
784 best match, i.e. the match with the fewest wildcards.
786 Thus a secrets file contains both secrets for use in authenticating
787 other hosts, plus secrets which we use for authenticating ourselves to
788 others. When pppd is authenticating the peer (checking the peer's
789 identity), it chooses a secret with the peer's name in the first
790 field and the name of the local system in the second field. The
791 name of the local system defaults to the hostname, with the domain
792 name appended if the \fIdomain\fR option is used. This default can be
793 overridden with the \fIname\fR option, except when the
794 \fIusehostname\fR option is used.
796 When pppd is choosing a secret to use in authenticating itself to the
797 peer, it first determines what name it is going to use to identify
798 itself to the peer. This name can be specified by the user with the
799 \fIuser\fR option. If this option is not used, the name defaults to
800 the name of the local system, determined as described in the previous
801 paragraph. Then pppd looks for a secret with this name in the first
802 field and the peer's name in the second field. Pppd will know the
803 name of the peer if CHAP authentication is being used, because the
804 peer will have sent it in the challenge packet. However, if PAP is being
805 used, pppd will have to determine the peer's name from the options
806 specified by the user. The user can specify the peer's name directly
807 with the \fIremotename\fR option. Otherwise, if the remote IP address
808 was specified by a name (rather than in numeric form), that name will
809 be used as the peer's name. Failing that, pppd will use the null
810 string as the peer's name.
812 When authenticating the peer with PAP, the supplied password is first
813 compared with the secret from the secrets file. If the password
814 doesn't match the secret, the password is encrypted using crypt() and
815 checked against the secret again. Thus secrets for authenticating the
816 peer can be stored in encrypted form if desired. If the
817 \fIpapcrypt\fR option is given, the first (unencrypted) comparison is
818 omitted, for better security.
820 Furthermore, if the \fIlogin\fR option was specified, the username and
821 password are also checked against the system password database. Thus,
822 the system administrator can set up the pap-secrets file to allow PPP
823 access only to certain users, and to restrict the set of IP addresses
824 that each user can use. Typically, when using the \fIlogin\fR option,
825 the secret in /etc/ppp/pap-secrets would be "", which will match any
826 password supplied by the peer. This avoids the need to have the same
827 secret in two places.
829 Authentication must be satisfactorily completed before IPCP (or any
830 other Network Control Protocol) can be started. If the peer is
831 required to authenticate itself, and fails to do so, pppd will
832 terminated the link (by closing LCP). If IPCP negotiates an
833 unacceptable IP address for the remote host, IPCP will be closed. IP
834 packets can only be sent or received when IPCP is open.
836 In some cases it is desirable to allow some hosts which can't
837 authenticate themselves to connect and use one of a restricted set of
838 IP addresses, even when the local host generally requires
839 authentication. If the peer refuses to authenticate itself when
840 requested, pppd takes that as equivalent to authenticating with PAP
841 using the empty string for the username and password. Thus, by adding
842 a line to the pap-secrets file which specifies the empty string for
843 the client and password, it is possible to allow restricted access to
844 hosts which refuse to authenticate themselves.
847 When IPCP negotiation is completed successfully, pppd will inform the
848 kernel of the local and remote IP addresses for the ppp interface.
849 This is sufficient to create a host route to the remote end of the
850 link, which will enable the peers to exchange IP packets.
851 Communication with other machines generally requires further
852 modification to routing tables and/or ARP (Address Resolution
853 Protocol) tables. In most cases the \fIdefaultroute\fR and/or
854 \fIproxyarp\fR options are sufficient for this, but in some cases
855 further intervention is required. The /etc/ppp/ip-up script can be
858 Sometimes it is desirable to add a default route through the remote
859 host, as in the case of a machine whose only connection to the
860 Internet is through the ppp interface. The \fIdefaultroute\fR option
861 causes pppd to create such a default route when IPCP comes up, and
862 delete it when the link is terminated.
864 In some cases it is desirable to use proxy ARP, for example on a
865 server machine connected to a LAN, in order to allow other hosts to
866 communicate with the remote host. The \fIproxyarp\fR option causes
867 pppd to look for a network interface on the same subnet as the remote
868 host (an interface supporting broadcast and ARP, which is up and not a
869 point-to-point or loopback interface). If found, pppd creates a
870 permanent, published ARP entry with the IP address of the remote host
871 and the hardware address of the network interface found.
873 When the \fIdemand\fR option is used, the interface IP addresses have
874 already been set at the point when IPCP comes up. If pppd has not
875 been able to negotiate the same addresses that it used to configure
876 the interface (for example when the peer is an ISP that uses dynamic
877 IP address assignment), pppd has to change the interface IP addresses
878 to the negotiated addresses. This may disrupt existing connections,
879 and the use of demand dialling with peers that do dynamic IP address
880 assignment is not recommended.
883 The following examples assume that the /etc/ppp/options file contains
884 the \fIauth\fR option (as in the default /etc/ppp/options file in the
887 Probably the most common use of pppd is to dial out to an ISP. This
888 can be done with a command such as
892 where the /etc/ppp/peers/isp file is set up by the system
893 administrator to contain something like this:
897 connect '/usr/sbin/chat -v -f /etc/ppp/chat-isp'
901 In this example, we are using chat to dial the ISP's modem and go
902 through any logon sequence required. The /etc/ppp/chat-isp file
903 contains the script used by chat; it could for example contain
916 ABORT "Username/Password Incorrect"
926 "word:" "\\qmypassword"
932 See the chat(8) man page for details of chat scripts.
934 Pppd can also be used to provide a dial-in ppp service for users. If
935 the users already have login accounts, the simplest way to set up the
936 ppp service is to let the users log in to their accounts and run pppd
937 (installed setuid-root) with a command such as
941 To allow a user to use the PPP facilities, you need to allocate an IP
942 address for that user's machine and create an entry in
943 /etc/ppp/pap-secrets or /etc/ppp/chap-secrets (depending on which
944 authentication method the PPP implementation on the user's machine
945 supports), so that the user's
946 machine can authenticate itself. For example, if Joe has a machine
947 called "joespc" which is to be allowed to dial in to the machine
948 called "server" and use the IP address joespc.my.net, you would add an
949 entry like this to /etc/ppp/pap-secrets or /etc/ppp/chap-secrets:
951 joespc server "joe's secret" joespc.my.net
953 Alternatively, you can create a username called (for example) "ppp",
954 whose login shell is pppd and whose home directory is /etc/ppp.
955 Options to be used when pppd is run this way can be put in
958 If your serial connection is any more complicated than a piece of
959 wire, you may need to arrange for some control characters to be
960 escaped. In particular, it is often useful to escape XON (^Q) and
961 XOFF (^S), using \fIasyncmap a0000\fR. If the path includes a telnet,
962 you probably should escape ^] as well (\fIasyncmap 200a0000\fR). If
963 the path includes an rlogin, you will need to use the \fIescape ff\fR
964 option on the end which is running the rlogin client, since many
965 rlogin implementations are not transparent; they will remove the
966 sequence [0xff, 0xff, 0x73, 0x73, followed by any 8 bytes] from the
970 Messages are sent to the syslog daemon using facility LOG_DAEMON.
971 (This can be overriden by recompiling pppd with the macro
972 LOG_PPP defined as the desired facility.) In order to see the error
973 and debug messages, you will need to edit your /etc/syslog.conf file
974 to direct the messages to the desired output device or file.
976 The \fIdebug\fR option causes the contents of all control packets sent
977 or received to be logged, that is, all LCP, PAP, CHAP or IPCP packets.
978 This can be useful if the PPP negotiation does not succeed or if
979 authentication fails.
980 If debugging is enabled at compile time, the \fIdebug\fR option also
981 causes other debugging messages to be logged.
983 Debugging can also be enabled or disabled by sending a SIGUSR1 signal
984 to the pppd process. This signal acts as a toggle.
986 Pppd invokes scripts at various stages in its processing which can be
987 used to perform site-specific ancillary processing. These scripts are
988 usually shell scripts, but could be executable code files instead.
989 Pppd does not wait for the scripts to finish. The scripts are
990 executed as root (with the real and effective user-id set to 0), so
991 that they can do things such as update routing tables or run
992 privileged daemons. Be careful that the contents of these scripts do
993 not compromise your system's security. Pppd runs the scripts with
994 standard input, output and error redirected to /dev/null, and with an
995 environment that is empty except for some environment variables that
996 give information about the link. The environment variables that pppd
1000 The name of the serial tty device being used.
1003 The name of the network interface being used.
1006 The IP address for the local end of the link. This is only set when
1010 The IP address for the remote end of the link. This is only set when
1014 The authenticated name of the peer. This is only set if the peer
1015 authenticates itself.
1018 The baud rate of the tty device.
1021 The real user-id of the user who invoked pppd.
1023 Pppd invokes the following scripts, if they exist. It is not an error
1024 if they don't exist.
1027 A program or script which is executed after the remote system
1028 successfully authenticates itself. It is executed with the parameters
1030 \fIinterface-name peer-name user-name tty-device speed\fR
1032 Note that this script is not executed if the peer doesn't authenticate
1033 itself, for example when the \fInoauth\fR option is used.
1035 .B /etc/ppp/auth-down
1036 A program or script which is executed when the link goes down, if
1037 /etc/ppp/auth-up was previously executed. It is executed in the same
1038 manner with the same parameters as /etc/ppp/auth-up.
1041 A program or script which is executed when the link is available for
1042 sending and receiving IP packets (that is, IPCP has come up). It is
1043 executed with the parameters
1045 \fIinterface-name tty-device speed local-IP-address
1046 remote-IP-address ipparam\fR
1049 A program or script which is executed when the link is no longer
1050 available for sending and receiving IP packets. This script can be
1051 used for undoing the effects of the /etc/ppp/ip-up script. It is
1052 invoked in the same manner and with the same parameters as the ip-up
1056 A program or script which is executed when the link is available for
1057 sending and receiving IPX packets (that is, IPXCP has come up). It is
1058 executed with the parameters
1060 \fIinterface-name tty-device speed network-number local-IPX-node-address
1061 remote-IPX-node-address local-IPX-routing-protocol remote-IPX-routing-protocol
1062 local-IPX-router-name remote-IPX-router-name ipparam pppd-pid\fR
1064 The local-IPX-routing-protocol and remote-IPX-routing-protocol field
1065 may be one of the following:
1067 NONE to indicate that there is no routing protocol
1069 RIP to indicate that RIP/SAP should be used
1071 NLSP to indicate that Novell NLSP should be used
1073 RIP NLSP to indicate that both RIP/SAP and NLSP should be used
1075 .B /etc/ppp/ipx-down
1076 A program or script which is executed when the link is no longer
1077 available for sending and receiving IPX packets. This script can be
1078 used for undoing the effects of the /etc/ppp/ipx-up script. It is
1079 invoked in the same manner and with the same parameters as the ipx-up
1083 .B /var/run/ppp\fIn\fB.pid \fR(BSD or Linux), \fB/etc/ppp/ppp\fIn\fB.pid \fR(others)
1084 Process-ID for pppd process on ppp interface unit \fIn\fR.
1086 .B /etc/ppp/pap-secrets
1087 Usernames, passwords and IP addresses for PAP authentication. This
1088 file should be owned by root and not readable or writable by any other
1089 user. Pppd will log a warning if this is not the case.
1091 .B /etc/ppp/chap-secrets
1092 Names, secrets and IP addresses for CHAP authentication. As for
1093 /etc/ppp/pap-secrets, this file should be owned by root and not
1094 readable or writable by any other user. Pppd will log a warning if
1095 this is not the case.
1098 System default options for pppd, read before user default options or
1099 command-line options.
1102 User default options, read before /etc/ppp/options.\fIttyname\fR.
1104 .B /etc/ppp/options.\fIttyname
1105 System default options for the serial port being used, read after
1106 ~/.ppprc. In forming the \fIttyname\fR part of this
1107 filename, an initial /dev/ is stripped from the port name (if
1108 present), and any slashes in the remaining part are converted to
1112 A directory containing options files which may contain privileged
1113 options, even if pppd was invoked by a user other than root. The
1114 system administrator can create options files in this directory to
1115 permit non-privileged users to dial out without requiring the peer to
1116 authenticate, but only to certain trusted peers.
1121 \fICompressing TCP/IP headers for low-speed serial links.\fR
1126 .I The MD5 Message-Digest Algorithm.
1131 .I PPP Internet Protocol Control Protocol (IPCP).
1135 Lloyd, B.; Simpson, W.A.
1136 .I PPP authentication protocols.
1141 .I The Point\-to\-Point Protocol (PPP).
1146 .I PPP in HDLC-like Framing.
1149 The following signals have the specified effect when sent to pppd.
1152 These signals cause pppd to terminate the link (by closing LCP),
1153 restore the serial device settings, and exit.
1156 This signal causes pppd to terminate the link, restore the serial
1157 device settings, and close the serial device. If the \fIpersist\fR or
1158 \fIdemand\fR option has been specified, pppd will try to reopen the
1159 serial device and start another connection (after the holdoff period).
1160 Otherwise pppd will exit. If this signal is received during the
1161 holdoff period, it causes pppd to end the holdoff period immediately.
1164 This signal toggles the state of the \fIdebug\fR option.
1167 This signal causes pppd to renegotiate compression. This can be
1168 useful to re-enable compression after it has been disabled as a result
1169 of a fatal decompression error. (Fatal decompression errors generally
1170 indicate a bug in one or other implementation.)
1173 Paul Mackerras (Paul.Mackerras@cs.anu.edu.au), based on earlier work by
projects / ppp.git / blob