1 .\" manual page [] for pppd 2.3
2 .\" $Id: pppd.8,v 1.32 1999/03/02 05:32:30 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.
43 Set the baud rate to <speed> (a decimal number). On systems such as
44 4.4BSD and NetBSD, any speed can be specified. Other systems
45 (e.g. SunOS) allow only a limited set of speeds.
47 .B active-filter \fIfilter-expression
48 Specifies a packet filter to be applied to data packets to determine
49 which packets are to be regarded as link activity, and therefore reset
50 the idle timer, or cause the link to be brought up in demand-dialling
51 mode. This option is useful in conjunction with the
52 \fBidle\fR option if there are packets being sent or received
53 regularly over the link (for example, routing information packets)
54 which would otherwise prevent the link from ever appearing to be idle.
55 The \fIfilter-expression\fR syntax is as described for tcpdump(1),
56 except that qualifiers which are inappropriate for a PPP link, such as
57 \fBether\fR and \fBarp\fR, are not permitted. Generally the filter
58 expression should be enclosed in single-quotes to prevent whitespace
59 in the expression from being interpreted by the shell. This option
60 is currently only available under NetBSD, and then only
61 if both the kernel and pppd were compiled with PPP_FILTER defined.
64 Set the async character map to <map>. This map describes which
65 control characters cannot be successfully received over the serial
66 line. Pppd will ask the peer to send these characters as a 2-byte
67 escape sequence. The argument is a 32 bit hex number with each bit
68 representing a character to escape. Bit 0 (00000001) represents the
69 character 0x00; bit 31 (80000000) represents the character 0x1f or ^_.
70 If multiple \fIasyncmap\fR options are given, the values are ORed
71 together. If no \fIasyncmap\fR option is given, no async character
72 map will be negotiated for the receive direction; the peer should then
73 escape \fIall\fR control characters. To escape transmitted
74 characters, use the \fIescape\fR option.
77 Require the peer to authenticate itself before allowing network
78 packets to be sent or received. This option is the default if the
79 system has a default route. If neither this option nor the
80 \fInoauth\fR option is specified, pppd will only allow the peer to use
81 IP addresses to which the system does not already have a route.
84 Read options from the file /etc/ppp/peers/\fIname\fR. This file may
85 contain privileged options, such as \fInoauth\fR, even if pppd
86 is not being run by root. The \fIname\fR string may not begin with /
87 or include .. as a pathname component. The format of the options file
91 Use the executable or shell command specified by \fIscript\fR to set
92 up the serial line. This script would typically use the chat(8)
93 program to dial the modem and start the remote ppp session. This
94 option is privileged if the \fInoauth\fR option is used.
97 Use hardware flow control (i.e. RTS/CTS) to control the flow of
98 data on the serial port. If neither the \fIcrtscts\fR, the
99 \fInocrtscts\fR, the \fIcdtrcts\fR nor the \fInocdtrcts\fR option
100 is given, the hardware flow control setting for the serial port is
102 Some serial ports (such as Macintosh serial ports) lack a true
103 RTS output. Such serial ports use this mode to implement
104 unidirectional flow control. The serial port will
105 suspend transmission when requested by the modem (via CTS)
106 but will be unable to request the modem stop sending to the
107 computer. This mode retains the ability to use DTR as
108 a modem control line.
111 Use a non-standard hardware flow control (i.e. DTR/CTS) to control
112 the flow of data on the serial port. If neither the \fIcrtscts\fR,
113 the \fInocrtscts\fR, the \fIcdtrcts\fR nor the \fInocdtrcts\fR
114 option is given, the hardware flow control setting for the serial
115 port is left unchanged.
116 Some serial ports (such as Macintosh serial ports) lack a true
117 RTS output. Such serial ports use this mode to implement true
118 bi-directional flow control. The sacrifice is that this flow
119 control mode does not permit using DTR as a modem control line.
122 Add a default route to the system routing tables, using the peer as
123 the gateway, when IPCP negotiation is successfully completed.
124 This entry is removed when the PPP connection is broken. This option
125 is privileged if the \fInodefaultroute\fR option has been specified.
127 .B disconnect \fIscript
128 Run the executable or shell command specified by \fIscript\fR after
129 pppd has terminated the link. This script could, for example, issue
130 commands to the modem to cause it to hang up if hardware modem control
131 signals were not available. The disconnect script is not run if the
132 modem has already hung up. This option is privileged if the
133 \fInoauth\fR option is used.
135 .B escape \fIxx,yy,...
136 Specifies that certain characters should be escaped on transmission
137 (regardless of whether the peer requests them to be escaped with its
138 async control character map). The characters to be escaped are
139 specified as a list of hex numbers separated by commas. Note that
140 almost any character can be specified for the \fIescape\fR option,
141 unlike the \fIasyncmap\fR option which only allows control characters
142 to be specified. The characters which may not be escaped are those
143 with hex values 0x20 - 0x3f or 0x5e.
146 Read options from file \fIname\fR (the format is described below).
147 The file must be readable by the user who has invoked pppd.
150 Specifies that pppd should create a UUCP-style lock file for the
151 serial device to ensure exclusive access to the device.
154 Set the MRU [Maximum Receive Unit] value to \fIn\fR. Pppd
155 will ask the peer to send packets of no more than \fIn\fR bytes. The
156 minimum MRU value is 128. The default MRU value is 1500. A value of
157 296 is recommended for slow links (40 bytes for TCP/IP header + 256
161 Set the MTU [Maximum Transmit Unit] value to \fIn\fR. Unless the
162 peer requests a smaller value via MRU negotiation, pppd will
163 request that the kernel networking code send data packets of no more
164 than \fIn\fR bytes through the PPP network interface.
167 Enables the "passive" option in the LCP. With this option, pppd will
168 attempt to initiate a connection; if no reply is received from the
169 peer, pppd will then just wait passively for a valid LCP packet from
170 the peer, instead of exiting, as it would without this option.
173 .I <local_IP_address>\fB:\fI<remote_IP_address>
174 Set the local and/or remote interface IP addresses. Either one may be
175 omitted. The IP addresses can be specified with a host name or in
176 decimal dot notation (e.g. 150.234.56.78). The default local
177 address is the (first) IP address of the system (unless the
179 option is given). The remote address will be obtained from the peer
180 if not specified in any option. Thus, in simple cases, this option is
181 not required. If a local and/or remote IP address is specified with
183 will not accept a different value from the peer in the IPCP
184 negotiation, unless the \fIipcp-accept-local\fR and/or
185 \fIipcp-accept-remote\fR options are given, respectively.
188 Request that the peer compress packets that it sends, using the
189 BSD-Compress scheme, with a maximum code size of \fInr\fR bits, and
190 agree to compress packets sent to the peer with a maximum code size of
191 \fInt\fR bits. If \fInt\fR is not specified, it defaults to the value
192 given for \fInr\fR. Values in the range 9 to 15 may be used for
193 \fInr\fR and \fInt\fR; larger values give better compression but
194 consume more kernel memory for compression dictionaries.
195 Alternatively, a value of 0 for \fInr\fR or \fInt\fR disables
196 compression in the corresponding direction. Use \fInobsdcomp\fR or
197 \fIbsdcomp 0\fR to disable BSD-Compress compression entirely.
199 .B chap-interval \fIn
200 If this option is given, pppd will rechallenge the peer every \fIn\fR
203 .B chap-max-challenge \fIn
204 Set the maximum number of CHAP challenge transmissions to \fIn\fR
208 Set the CHAP restart interval (retransmission timeout for challenges)
209 to \fIn\fR seconds (default 3).
212 Enables connection debugging facilities.
213 If this option is given, pppd will log the contents of all
214 control packets sent or received in a readable form. The packets are
215 logged through syslog with facility \fIdaemon\fR and level
216 \fIdebug\fR. This information can be directed to a file by setting up
217 /etc/syslog.conf appropriately (see syslog.conf(5)).
220 Disable asyncmap negotiation, forcing all control characters to be
221 escaped for both the transmit and the receive direction.
224 Disable MRU [Maximum Receive Unit] negotiation. With this option,
225 pppd will use the default MRU value of 1500 bytes for both the
226 transmit and receive direction.
229 Request that the peer compress packets that it sends, using the
230 Deflate scheme, with a maximum window size of \fI2**nr\fR bytes, and
231 agree to compress packets sent to the peer with a maximum window size
232 of \fI2**nt\fR bytes. If \fInt\fR is not specified, it defaults to
233 the value given for \fInr\fR. Values in the range 8 to 15 may be used
234 for \fInr\fR and \fInt\fR; larger values give better compression but
235 consume more kernel memory for compression dictionaries.
236 Alternatively, a value of 0 for \fInr\fR or \fInt\fR disables
237 compression in the corresponding direction. Use \fInodeflate\fR or
238 \fIdeflate 0\fR to disable Deflate compression entirely. (Note: pppd
239 requests Deflate compression in preference to BSD-Compress if the peer
243 Initiate the link only on demand, i.e. when data traffic is present.
244 With this option, the remote IP address must be specified by the user
245 on the command line or in an options file. Pppd will initially
246 configure the interface and enable it for IP traffic without
247 connecting to the peer. When traffic is available, pppd will
248 connect to the peer and perform negotiation, authentication, etc.
249 When this is completed, pppd will commence passing data packets
250 (i.e., IP packets) across the link.
252 The \fIdemand\fR option implies the \fIpersist\fR option. If this
253 behaviour is not desired, use the \fInopersist\fR option after the
254 \fIdemand\fR option. The \fIidle\fR and \fIholdoff\fR
255 options are also useful in conjuction with the \fIdemand\fR option.
258 Append the domain name \fId\fR to the local host name for authentication
259 purposes. For example, if gethostname() returns the name porsche, but
260 the fully qualified domain name is porsche.Quotron.COM, you could
261 specify \fIdomain Quotron.COM\fR. Pppd would then use the name
262 \fIporsche.Quotron.COM\fR for looking up secrets in the secrets file,
263 and as the default name to send to the peer when authenticating itself
264 to the peer. This option is privileged.
267 When logging the contents of PAP packets, this option causes pppd to
268 exclude the password string from the log.
270 Specifies how many seconds to wait before re-initiating the link after
271 it terminates. This option only has any effect if the \fIpersist\fR
272 or \fIdemand\fR option is used. The holdoff period is not applied if
273 the link was terminated because it was idle.
276 Specifies that pppd should disconnect if the link is idle for \fIn\fR
277 seconds. The link is idle when no data packets (i.e. IP packets) are
278 being sent or received. Note: it is not advisable to use this option
279 with the \fIpersist\fR option without the \fIdemand\fR option.
280 If the \fBactive-filter\fR
281 option is given, data packets which are rejected by the specified
282 activity filter also count as the link being idle.
285 With this option, pppd will accept the peer's idea of our local IP
286 address, even if the local IP address was specified in an option.
288 .B ipcp-accept-remote
289 With this option, pppd will accept the peer's idea of its (remote) IP
290 address, even if the remote IP address was specified in an option.
292 .B ipcp-max-configure \fIn
293 Set the maximum number of IPCP configure-request transmissions to
294 \fIn\fR (default 10).
296 .B ipcp-max-failure \fIn
297 Set the maximum number of IPCP configure-NAKs returned before starting
298 to send configure-Rejects instead to \fIn\fR (default 10).
300 .B ipcp-max-terminate \fIn
301 Set the maximum number of IPCP terminate-request transmissions to
305 Set the IPCP restart interval (retransmission timeout) to \fIn\fR
309 Provides an extra parameter to the ip-up and ip-down scripts. If this
310 option is given, the \fIstring\fR supplied is given as the 6th
311 parameter to those scripts.
314 Enable the IPXCP and IPX protocols. This option is presently only
315 supported under Linux, and only if your kernel has been configured to
319 Set the IPX network number in the IPXCP configure request frame to
320 \fIn\fR, a hexadecimal number (without a leading 0x). There is no
321 valid default. If this option is not specified, the network number is
322 obtained from the peer. If the peer does not have the network number,
323 the IPX protocol will not be started.
325 .B ipx-node \fIn\fB:\fIm
326 Set the IPX node numbers. The two node numbers are separated from each
327 other with a colon character. The first number \fIn\fR is the local
328 node number. The second number \fIm\fR is the peer's node number. Each
329 node number is a hexadecimal number, at most 10 digits long. The node
330 numbers on the ipx-network must be unique. There is no valid
331 default. If this option is not specified then the node numbers are
332 obtained from the peer.
334 .B ipx-router-name \fI<string>
335 Set the name of the router. This is a string and is sent to the peer
339 Set the routing protocol to be received by this option. More than one
340 instance of \fIipx-routing\fR may be specified. The '\fInone\fR'
341 option (0) may be specified as the only instance of ipx-routing. The
342 values may be \fI0\fR for \fINONE\fR, \fI2\fR for \fIRIP/SAP\fR, and
343 \fI4\fR for \fINLSP\fR.
345 .B ipxcp-accept-local
346 Accept the peer's NAK for the node number specified in the ipx-node
347 option. If a node number was specified, and non-zero, the default is
348 to insist that the value be used. If you include this option then you
349 will permit the peer to override the entry of the node number.
351 .B ipxcp-accept-network
352 Accept the peer's NAK for the network number specified in the
353 ipx-network option. If a network number was specified, and non-zero, the
354 default is to insist that the value be used. If you include this
355 option then you will permit the peer to override the entry of the node
358 .B ipxcp-accept-remote
359 Use the peer's network number specified in the configure request
360 frame. If a node number was specified for the peer and this option was
361 not specified, the peer will be forced to use the value which you have
364 .B ipxcp-max-configure \fIn
365 Set the maximum number of IPXCP configure request frames which the
366 system will send to \fIn\fR. The default is 10.
368 .B ipxcp-max-failure \fIn
369 Set the maximum number of IPXCP NAK frames which the local system will
370 send before it rejects the options. The default value is 3.
372 .B ipxcp-max-terminate \fIn
373 Set the maximum nuber of IPXCP terminate request frames before the
374 local system considers that the peer is not listening to them. The
378 Enable debugging code in the kernel-level PPP driver. The argument
379 \fIn\fR is a number which is the sum of the following values: 1 to
380 enable general debug messages, 2 to request that the contents of
381 received packets be printed, and 4 to request that the contents of
382 transmitted packets be printed. On most systems, messages printed by
383 the kernel are logged by syslog(1) to a file as directed in the
384 /etc/syslog.conf configuration file.
386 .B lcp-echo-failure \fIn
387 If this option is given, pppd will presume the peer to be dead
388 if \fIn\fR LCP echo-requests are sent without receiving a valid LCP
389 echo-reply. If this happens, pppd will terminate the
390 connection. Use of this option requires a non-zero value for the
391 \fIlcp-echo-interval\fR parameter. This option can be used to enable
392 pppd to terminate after the physical connection has been broken
393 (e.g., the modem has hung up) in situations where no hardware modem
394 control lines are available.
396 .B lcp-echo-interval \fIn
397 If this option is given, pppd will send an LCP echo-request frame to
398 the peer every \fIn\fR seconds. Normally the peer should respond to
399 the echo-request by sending an echo-reply. This option can be used
400 with the \fIlcp-echo-failure\fR option to detect that the peer is no
403 .B lcp-max-configure \fIn
404 Set the maximum number of LCP configure-request transmissions to
405 \fIn\fR (default 10).
407 .B lcp-max-failure \fIn
408 Set the maximum number of LCP configure-NAKs returned before starting
409 to send configure-Rejects instead to \fIn\fR (default 10).
411 .B lcp-max-terminate \fIn
412 Set the maximum number of LCP terminate-request transmissions to
416 Set the LCP restart interval (retransmission timeout) to \fIn\fR
420 Don't use the modem control lines. With this option, pppd will ignore
421 the state of the CD (Carrier Detect) signal from the modem and will
422 not change the state of the DTR (Data Terminal Ready) signal.
425 Use the system password database for authenticating the peer using
426 PAP, and record the user in the system wtmp file. Note that the peer
427 must have an entry in the /etc/ppp/pap-secrets file as well as the
428 system password database to be allowed access.
431 Terminate the connection when it has been available for network
432 traffic for \fIn\fR seconds (i.e. \fIn\fR seconds after the first
433 network control protocol comes up).
436 Use the modem control lines. This option is the default. With this
437 option, pppd will wait for the CD (Carrier Detect) signal from the
438 modem to be asserted when opening the serial device (unless a connect
439 script is specified), and it will drop the DTR (Data Terminal Ready)
440 signal briefly when the connection is terminated and before executing
441 the connect script. On Ultrix, this option implies hardware flow
442 control, as for the \fIcrtscts\fR option.
445 If pppd is acting as a server for Microsoft Windows clients, this
446 option allows pppd to supply one or two DNS (Domain Name Server)
447 addresses to the clients. The first instance of this option specifies
448 the primary DNS address; the second instance (if given) specifies the
449 secondary DNS address. (This option was present in some older
450 versions of pppd under the name \fBdns-addr\fR.)
453 If pppd is acting as a server for Microsoft Windows or "Samba"
454 clients, this option allows pppd to supply one or two WINS (Windows
455 Internet Name Services) server addresses to the clients. The first
456 instance of this option specifies the primary WINS address; the second
457 instance (if given) specifies the secondary WINS address.
460 Set the name of the local system for authentication purposes to
461 \fIname\fR. This is a privileged option. With this option, pppd will
462 use lines in the secrets files which have \fIname\fR as the second
463 field when looking for a secret to use in authenticating the peer. In
464 addition, unless overridden with the \fIuser\fR option, \fIname\fR
465 will be used as the name to send to the peer when authenticating the
466 local system to the peer. (Note that pppd does not append the domain
470 Set the interface netmask to \fIn\fR, a 32 bit netmask in "decimal dot"
471 notation (e.g. 255.255.255.0). If this option is given, the value
472 specified is ORed with the default netmask. The default netmask is
473 chosen based on the negotiated remote IP address; it is the
474 appropriate network mask for the class of the remote IP address, ORed
475 with the netmasks for any non point-to-point network interfaces in the
476 system which are on the same network. (Note: on some platforms, pppd
477 will always use 255.255.255.255 for the netmask, if that is the only
478 appropriate value for a point-to-point interface.)
481 Disable Address/Control compression in both directions (send and
485 Do not require the peer to authenticate itself. This option is
489 Disables BSD-Compress compression; \fBpppd\fR will not request or
490 agree to compress packets using the BSD-Compress scheme.
493 Disable CCP (Compression Control Protocol) negotiation. This option
494 should only be required if the peer is buggy and gets confused by
495 requests from pppd for CCP negotiation.
498 Disable hardware flow control (i.e. RTS/CTS) on the serial port.
499 If neither the \fIcrtscts\fR nor the \fInocrtscts\fR nor the
500 \fIcdtrcts\fR nor the \fInodtrcts\fR option is given, the hardware
501 flow control setting for the serial port is left unchanged.
504 This option is a synonym for \fInocrtscts\fR. Either of these options will
505 disable both forms of hardware flow control.
508 Disable the \fIdefaultroute\fR option. The system administrator who
509 wishes to prevent users from creating default routes with pppd
510 can do so by placing this option in the /etc/ppp/options file.
513 Disables Deflate compression; pppd will not request or agree to
514 compress packets using the Deflate scheme.
517 Don't detach from the controlling terminal. Without this option, if a
518 serial device other than the terminal on the standard input is
519 specified, pppd will fork to become a background process.
522 Disable IPCP negotiation and IP communication. This option should
523 only be required if the peer is buggy and gets confused by requests
524 from pppd for IPCP negotiation.
527 Disables the default behaviour when no local IP address is specified,
528 which is to determine (if possible) the local IP address from the
529 hostname. With this option, the peer will have to supply the local IP
530 address during IPCP negotiation (unless it specified explicitly on the
531 command line or in an options file).
534 Disable the IPXCP and IPX protocols. This option should only be
535 required if the peer is buggy and gets confused by requests from pppd
536 for IPXCP negotiation.
539 Disable magic number negotiation. With this option, pppd cannot
540 detect a looped-back line. This option should only be needed if the
544 Disable protocol field compression negotiation in both the receive and
545 the transmit direction.
548 Exit once a connection has been made and terminated. This is the
549 default unless the \fIpersist\fR or \fIdemand\fR option has been
553 Do not accept or agree to Predictor-1 comprssion.
556 Disable the \fIproxyarp\fR option. The system administrator who
557 wishes to prevent users from creating proxy ARP entries with pppd can
558 do so by placing this option in the /etc/ppp/options file.
561 Disable Van Jacobson style TCP/IP header compression in both the
562 transmit and the receive direction.
565 Disable the connection-ID compression option in Van Jacobson style
566 TCP/IP header compression. With this option, pppd will not omit the
567 connection-ID byte from Van Jacobson compressed TCP/IP headers, nor
568 ask the peer to do so.
571 Indicates that all secrets in the /etc/ppp/pap-secrets file which are
572 used for checking the identity of the peer are encrypted, and thus
573 pppd should not accept a password which, before encryption, is
574 identical to the secret from the /etc/ppp/pap-secrets file.
576 .B pap-max-authreq \fIn
577 Set the maximum number of PAP authenticate-request transmissions to
578 \fIn\fR (default 10).
581 Set the PAP restart interval (retransmission timeout) to \fIn\fR
585 Set the maximum time that pppd will wait for the peer to authenticate
586 itself with PAP to \fIn\fR seconds (0 means no limit).
588 .B pass-filter \fIfilter-expression
589 Specifies a packet filter to applied to data packets being sent or
590 received to determine which packets should be allowed to pass.
591 Packets which are rejected by the filter are silently discarded. This
592 option can be used to prevent specific network daemons (such as
593 routed) using up link bandwidth, or to provide a basic firewall
595 The \fIfilter-expression\fR syntax is as described for tcpdump(1),
596 except that qualifiers which are inappropriate for a PPP link, such as
597 \fBether\fR and \fBarp\fR, are not permitted. Generally the filter
598 expression should be enclosed in single-quotes to prevent whitespace
599 in the expression from being interpreted by the shell. Note that it
600 is possible to apply different constraints to incoming and outgoing
601 packets using the \fBinbound\fR and \fBoutbound\fR qualifiers. This
602 option is currently only available under NetBSD, and then only if both
603 the kernel and pppd were compiled with PPP_FILTER defined.
606 Do not exit after a connection is terminated; instead try to reopen
610 Request that the peer compress frames that it sends using Predictor-1
611 compression, and agree to compress transmitted frames with Predictor-1
612 if requested. This option has no effect unless the kernel driver
613 supports Predictor-1 compression.
616 Add an entry to this system's ARP [Address Resolution Protocol] table
617 with the IP address of the peer and the Ethernet address of this
618 system. This will have the effect of making the peer appear to other
619 systems to be on the local ethernet.
621 .B remotename \fIname
622 Set the assumed name of the remote system for authentication purposes
626 With this option, pppd will not agree to authenticate itself to the
630 With this option, pppd will not agree to authenticate itself to the
634 Require the peer to authenticate itself using CHAP [Challenge
635 Handshake Authentication Protocol] authentication.
638 Require the peer to authenticate itself using PAP [Password
639 Authentication Protocol] authentication.
642 With this option, pppd will not transmit LCP packets to initiate a
643 connection until a valid LCP packet is received from the peer (as for
644 the `passive' option with ancient versions of pppd).
647 Enforce the use of the hostname (with domain name appended, if given)
648 as the name of the local system for authentication purposes (overrides
649 the \fIname\fR option). This option is not normally needed since the
650 \fIname\fR option is privileged.
653 Sets the name used for authenticating the local system to the peer to
657 Sets the number of connection slots to be used by the Van Jacobson
658 TCP/IP header compression and decompression code to \fIn\fR, which
659 must be between 2 and 16 (inclusive).
662 Run the executable or shell command specified by \fIscript\fR before
663 initiating PPP negotiation, after the connect script (if any) has
664 completed. This option is privileged if the \fInoauth\fR option is
668 Use software flow control (i.e. XON/XOFF) to control the flow of data on
671 Options can be taken from files as well as the command line. Pppd
672 reads options from the files /etc/ppp/options, ~/.ppprc and
673 /etc/ppp/options.\fIttyname\fR (in that order) before processing the
674 options on the command line. (In fact, the command-line options are
675 scanned to find the terminal name before the options.\fIttyname\fR
676 file is read.) In forming the name of the options.\fIttyname\fR file,
677 the initial /dev/ is removed from the terminal name, and any remaining
678 / characters are replaced with dots.
680 An options file is parsed into a series of words, delimited by
681 whitespace. Whitespace can be included in a word by enclosing the
682 word in double-quotes ("). A backslash (\\) quotes the following character.
683 A hash (#) starts a comment, which continues until the end of the
684 line. There is no restriction on using the \fIfile\fR or \fIcall\fR
685 options within an options file.
688 provides system administrators with sufficient access control that PPP
689 access to a server machine can be provided to legitimate users without
690 fear of compromising the security of the server or the network it's
691 on. This control is provided through restrictions on which IP
692 addresses the peer may use, based on its authenticated identity (if
693 any), and through restrictions on which options a non-privileged user
694 may use. Several of pppd's options are privileged, in particular
695 those which permit potentially insecure configurations; these options
696 are only accepted in files which are under the control of the system
697 administrator, or if pppd is being run by root.
699 The default behaviour of pppd is to allow an unauthenticated peer
700 to use a given IP address if the system does not already have a
701 route to that IP address already. For example, a system with a
702 permanent connection to the wider internet will normally have a
703 default route, and thus all peers will have to authenticate themselves
704 in order to set up a connection. On such a system, the \fIauth\fR
705 option should be used in /etc/ppp/options so that pppd will ask the
706 peer to authenticate itself. On the other hand, a system where the
707 PPP link is the only connection to the internet will not normally have
708 a default route, so the peer will be able to use almost any IP address
709 without authenticating itself.
711 As indicated above, some security-sensitive options are privileged,
712 which means that they may not be used by an ordinary non-privileged
713 user running a setuid-root pppd, either on the command line, in the
714 user's ~/.ppprc file, or in an options file read using the \fIfile\fR
715 option. Privileged options may be used in /etc/ppp/options file or in
716 an options file read using the \fIcall\fR option. If pppd is being
717 run by the root user, privileged options can be used without
720 Authentication is the process whereby one peer convinces the other of
721 its identity. This involves the first peer sending its name to the
722 other, together with some kind of secret information which could only
723 come from the genuine authorized user of that name. In such an
724 exchange, we will call the first peer the "client" and the other the
725 "server". The client has a name by which it identifies itself to the
726 server, and the server also has a name by which it identifies itself
727 to the client. Generally the genuine client shares some secret (or
728 password) with the server, and authenticates itself by proving that it
729 knows that secret. Very often, the names used for authentication
730 correspond to the internet hostnames of the peers, but this is not
733 At present, pppd supports two authentication protocols: the Password
734 Authentication Protocol (PAP) and the Challenge Handshake
735 Authentication Protocol (CHAP). PAP involves the client sending its
736 name and a cleartext password to the server to authenticate itself.
737 In contrast, the server initiates the CHAP authentication exchange by
738 sending a challenge to the client (the challenge packet includes the
739 server's name). The client must respond with a response which
740 includes its name plus a hash value derived from the shared secret and
741 the challenge, in order to prove that it knows the secret.
743 The PPP protocol, being symmetrical, allows both peers to require the
744 other to authenticate itself. In that case, two separate and
745 independent authentication exchanges will occur. The two exchanges
746 could use different authentication protocols, and in principle,
747 different names could be used in the two exchanges.
749 The default behaviour of pppd is to agree to authenticate if
750 requested, and to not require authentication from the peer. However,
751 pppd will not agree to authenticate itself with a particular protocol
752 if it has no secrets which could be used to do so.
754 Pppd stores secrets for use in authentication in secrets
755 files (/etc/ppp/pap-secrets for PAP, /etc/ppp/chap-secrets for CHAP).
756 Both secrets files have the same format. The secrets files can
757 contain secrets for pppd to use in authenticating itself to other
758 systems, as well as secrets for pppd to use when authenticating other
761 Each line in a secrets file contains one secret. A given secret is
762 specific to a particular combination of client and server - it can
763 only be used by that client to authenticate itself to that server.
764 Thus each line in a secrets file has at least 3 fields: the name of
765 the client, the name of the server, and the secret. These fields may
766 be followed by a list of the IP addresses that the specified client
767 may use when connecting to the specified server.
769 A secrets file is parsed into words as for a options file, so the
770 client name, server name and secrets fields must each be one word,
771 with any embedded spaces or other special characters quoted or
772 escaped. Any following words on the same line are taken to be a list
773 of acceptable IP addresses for that client. If there are only 3 words
774 on the line, or if the first word is "-", then all IP addresses are
775 disallowed. To allow any address, use "*".
776 A word starting with "!" indicates that the
777 specified address is \fInot\fR acceptable. An address may be followed
778 by "/" and a number \fIn\fR, to indicate a whole subnet, i.e. all
779 addresses which have the same value in the most significant \fIn\fR
780 bits. Note that case is significant in the client and server names
783 If the secret starts with an `@', what follows is assumed to be the
784 name of a file from which to read the secret. A "*" as the client or
785 server name matches any name. When selecting a secret, pppd takes the
786 best match, i.e. the match with the fewest wildcards.
788 Thus a secrets file contains both secrets for use in authenticating
789 other hosts, plus secrets which we use for authenticating ourselves to
790 others. When pppd is authenticating the peer (checking the peer's
791 identity), it chooses a secret with the peer's name in the first
792 field and the name of the local system in the second field. The
793 name of the local system defaults to the hostname, with the domain
794 name appended if the \fIdomain\fR option is used. This default can be
795 overridden with the \fIname\fR option, except when the
796 \fIusehostname\fR option is used.
798 When pppd is choosing a secret to use in authenticating itself to the
799 peer, it first determines what name it is going to use to identify
800 itself to the peer. This name can be specified by the user with the
801 \fIuser\fR option. If this option is not used, the name defaults to
802 the name of the local system, determined as described in the previous
803 paragraph. Then pppd looks for a secret with this name in the first
804 field and the peer's name in the second field. Pppd will know the
805 name of the peer if CHAP authentication is being used, because the
806 peer will have sent it in the challenge packet. However, if PAP is being
807 used, pppd will have to determine the peer's name from the options
808 specified by the user. The user can specify the peer's name directly
809 with the \fIremotename\fR option. Otherwise, if the remote IP address
810 was specified by a name (rather than in numeric form), that name will
811 be used as the peer's name. Failing that, pppd will use the null
812 string as the peer's name.
814 When authenticating the peer with PAP, the supplied password is first
815 compared with the secret from the secrets file. If the password
816 doesn't match the secret, the password is encrypted using crypt() and
817 checked against the secret again. Thus secrets for authenticating the
818 peer can be stored in encrypted form if desired. If the
819 \fIpapcrypt\fR option is given, the first (unencrypted) comparison is
820 omitted, for better security.
822 Furthermore, if the \fIlogin\fR option was specified, the username and
823 password are also checked against the system password database. Thus,
824 the system administrator can set up the pap-secrets file to allow PPP
825 access only to certain users, and to restrict the set of IP addresses
826 that each user can use. Typically, when using the \fIlogin\fR option,
827 the secret in /etc/ppp/pap-secrets would be "", which will match any
828 password supplied by the peer. This avoids the need to have the same
829 secret in two places.
831 Authentication must be satisfactorily completed before IPCP (or any
832 other Network Control Protocol) can be started. If the peer is
833 required to authenticate itself, and fails to do so, pppd will
834 terminated the link (by closing LCP). If IPCP negotiates an
835 unacceptable IP address for the remote host, IPCP will be closed. IP
836 packets can only be sent or received when IPCP is open.
838 In some cases it is desirable to allow some hosts which can't
839 authenticate themselves to connect and use one of a restricted set of
840 IP addresses, even when the local host generally requires
841 authentication. If the peer refuses to authenticate itself when
842 requested, pppd takes that as equivalent to authenticating with PAP
843 using the empty string for the username and password. Thus, by adding
844 a line to the pap-secrets file which specifies the empty string for
845 the client and password, it is possible to allow restricted access to
846 hosts which refuse to authenticate themselves.
849 When IPCP negotiation is completed successfully, pppd will inform the
850 kernel of the local and remote IP addresses for the ppp interface.
851 This is sufficient to create a host route to the remote end of the
852 link, which will enable the peers to exchange IP packets.
853 Communication with other machines generally requires further
854 modification to routing tables and/or ARP (Address Resolution
855 Protocol) tables. In most cases the \fIdefaultroute\fR and/or
856 \fIproxyarp\fR options are sufficient for this, but in some cases
857 further intervention is required. The /etc/ppp/ip-up script can be
860 Sometimes it is desirable to add a default route through the remote
861 host, as in the case of a machine whose only connection to the
862 Internet is through the ppp interface. The \fIdefaultroute\fR option
863 causes pppd to create such a default route when IPCP comes up, and
864 delete it when the link is terminated.
866 In some cases it is desirable to use proxy ARP, for example on a
867 server machine connected to a LAN, in order to allow other hosts to
868 communicate with the remote host. The \fIproxyarp\fR option causes
869 pppd to look for a network interface on the same subnet as the remote
870 host (an interface supporting broadcast and ARP, which is up and not a
871 point-to-point or loopback interface). If found, pppd creates a
872 permanent, published ARP entry with the IP address of the remote host
873 and the hardware address of the network interface found.
875 When the \fIdemand\fR option is used, the interface IP addresses have
876 already been set at the point when IPCP comes up. If pppd has not
877 been able to negotiate the same addresses that it used to configure
878 the interface (for example when the peer is an ISP that uses dynamic
879 IP address assignment), pppd has to change the interface IP addresses
880 to the negotiated addresses. This may disrupt existing connections,
881 and the use of demand dialling with peers that do dynamic IP address
882 assignment is not recommended.
885 The following examples assume that the /etc/ppp/options file contains
886 the \fIauth\fR option (as in the default /etc/ppp/options file in the
889 Probably the most common use of pppd is to dial out to an ISP. This
890 can be done with a command such as
894 where the /etc/ppp/peers/isp file is set up by the system
895 administrator to contain something like this:
899 connect '/usr/sbin/chat -v -f /etc/ppp/chat-isp'
903 In this example, we are using chat to dial the ISP's modem and go
904 through any logon sequence required. The /etc/ppp/chat-isp file
905 contains the script used by chat; it could for example contain
918 ABORT "Username/Password Incorrect"
928 "word:" "\\qmypassword"
934 See the chat(8) man page for details of chat scripts.
936 Pppd can also be used to provide a dial-in ppp service for users. If
937 the users already have login accounts, the simplest way to set up the
938 ppp service is to let the users log in to their accounts and run pppd
939 (installed setuid-root) with a command such as
943 To allow a user to use the PPP facilities, you need to allocate an IP
944 address for that user's machine and create an entry in
945 /etc/ppp/pap-secrets or /etc/ppp/chap-secrets (depending on which
946 authentication method the PPP implementation on the user's machine
947 supports), so that the user's
948 machine can authenticate itself. For example, if Joe has a machine
949 called "joespc" which is to be allowed to dial in to the machine
950 called "server" and use the IP address joespc.my.net, you would add an
951 entry like this to /etc/ppp/pap-secrets or /etc/ppp/chap-secrets:
953 joespc server "joe's secret" joespc.my.net
955 Alternatively, you can create a username called (for example) "ppp",
956 whose login shell is pppd and whose home directory is /etc/ppp.
957 Options to be used when pppd is run this way can be put in
960 If your serial connection is any more complicated than a piece of
961 wire, you may need to arrange for some control characters to be
962 escaped. In particular, it is often useful to escape XON (^Q) and
963 XOFF (^S), using \fIasyncmap a0000\fR. If the path includes a telnet,
964 you probably should escape ^] as well (\fIasyncmap 200a0000\fR). If
965 the path includes an rlogin, you will need to use the \fIescape ff\fR
966 option on the end which is running the rlogin client, since many
967 rlogin implementations are not transparent; they will remove the
968 sequence [0xff, 0xff, 0x73, 0x73, followed by any 8 bytes] from the
972 Messages are sent to the syslog daemon using facility LOG_DAEMON.
973 (This can be overriden by recompiling pppd with the macro
974 LOG_PPP defined as the desired facility.) In order to see the error
975 and debug messages, you will need to edit your /etc/syslog.conf file
976 to direct the messages to the desired output device or file.
978 The \fIdebug\fR option causes the contents of all control packets sent
979 or received to be logged, that is, all LCP, PAP, CHAP or IPCP packets.
980 This can be useful if the PPP negotiation does not succeed or if
981 authentication fails.
982 If debugging is enabled at compile time, the \fIdebug\fR option also
983 causes other debugging messages to be logged.
985 Debugging can also be enabled or disabled by sending a SIGUSR1 signal
986 to the pppd process. This signal acts as a toggle.
988 Pppd invokes scripts at various stages in its processing which can be
989 used to perform site-specific ancillary processing. These scripts are
990 usually shell scripts, but could be executable code files instead.
991 Pppd does not wait for the scripts to finish. The scripts are
992 executed as root (with the real and effective user-id set to 0), so
993 that they can do things such as update routing tables or run
994 privileged daemons. Be careful that the contents of these scripts do
995 not compromise your system's security. Pppd runs the scripts with
996 standard input, output and error redirected to /dev/null, and with an
997 environment that is empty except for some environment variables that
998 give information about the link. The environment variables that pppd
1002 The name of the serial tty device being used.
1005 The name of the network interface being used.
1008 The IP address for the local end of the link. This is only set when
1012 The IP address for the remote end of the link. This is only set when
1016 The authenticated name of the peer. This is only set if the peer
1017 authenticates itself.
1020 The baud rate of the tty device.
1023 The real user-id of the user who invoked pppd.
1025 Pppd invokes the following scripts, if they exist. It is not an error
1026 if they don't exist.
1029 A program or script which is executed after the remote system
1030 successfully authenticates itself. It is executed with the parameters
1032 \fIinterface-name peer-name user-name tty-device speed\fR
1034 Note that this script is not executed if the peer doesn't authenticate
1035 itself, for example when the \fInoauth\fR option is used.
1037 .B /etc/ppp/auth-down
1038 A program or script which is executed when the link goes down, if
1039 /etc/ppp/auth-up was previously executed. It is executed in the same
1040 manner with the same parameters as /etc/ppp/auth-up.
1043 A program or script which is executed when the link is available for
1044 sending and receiving IP packets (that is, IPCP has come up). It is
1045 executed with the parameters
1047 \fIinterface-name tty-device speed local-IP-address
1048 remote-IP-address ipparam\fR
1051 A program or script which is executed when the link is no longer
1052 available for sending and receiving IP packets. This script can be
1053 used for undoing the effects of the /etc/ppp/ip-up script. It is
1054 invoked in the same manner and with the same parameters as the ip-up
1058 A program or script which is executed when the link is available for
1059 sending and receiving IPX packets (that is, IPXCP has come up). It is
1060 executed with the parameters
1062 \fIinterface-name tty-device speed network-number local-IPX-node-address
1063 remote-IPX-node-address local-IPX-routing-protocol remote-IPX-routing-protocol
1064 local-IPX-router-name remote-IPX-router-name ipparam pppd-pid\fR
1066 The local-IPX-routing-protocol and remote-IPX-routing-protocol field
1067 may be one of the following:
1069 NONE to indicate that there is no routing protocol
1071 RIP to indicate that RIP/SAP should be used
1073 NLSP to indicate that Novell NLSP should be used
1075 RIP NLSP to indicate that both RIP/SAP and NLSP should be used
1077 .B /etc/ppp/ipx-down
1078 A program or script which is executed when the link is no longer
1079 available for sending and receiving IPX packets. This script can be
1080 used for undoing the effects of the /etc/ppp/ipx-up script. It is
1081 invoked in the same manner and with the same parameters as the ipx-up
1085 .B /var/run/ppp\fIn\fB.pid \fR(BSD or Linux), \fB/etc/ppp/ppp\fIn\fB.pid \fR(others)
1086 Process-ID for pppd process on ppp interface unit \fIn\fR.
1088 .B /etc/ppp/pap-secrets
1089 Usernames, passwords and IP addresses for PAP authentication. This
1090 file should be owned by root and not readable or writable by any other
1091 user. Pppd will log a warning if this is not the case.
1093 .B /etc/ppp/chap-secrets
1094 Names, secrets and IP addresses for CHAP authentication. As for
1095 /etc/ppp/pap-secrets, this file should be owned by root and not
1096 readable or writable by any other user. Pppd will log a warning if
1097 this is not the case.
1100 System default options for pppd, read before user default options or
1101 command-line options.
1104 User default options, read before /etc/ppp/options.\fIttyname\fR.
1106 .B /etc/ppp/options.\fIttyname
1107 System default options for the serial port being used, read after
1108 ~/.ppprc. In forming the \fIttyname\fR part of this
1109 filename, an initial /dev/ is stripped from the port name (if
1110 present), and any slashes in the remaining part are converted to
1114 A directory containing options files which may contain privileged
1115 options, even if pppd was invoked by a user other than root. The
1116 system administrator can create options files in this directory to
1117 permit non-privileged users to dial out without requiring the peer to
1118 authenticate, but only to certain trusted peers.
1123 \fICompressing TCP/IP headers for low-speed serial links.\fR
1128 .I The MD5 Message-Digest Algorithm.
1133 .I PPP Internet Protocol Control Protocol (IPCP).
1137 Lloyd, B.; Simpson, W.A.
1138 .I PPP authentication protocols.
1143 .I The Point\-to\-Point Protocol (PPP).
1148 .I PPP in HDLC-like Framing.
1151 The following signals have the specified effect when sent to pppd.
1154 These signals cause pppd to terminate the link (by closing LCP),
1155 restore the serial device settings, and exit.
1158 This signal causes pppd to terminate the link, restore the serial
1159 device settings, and close the serial device. If the \fIpersist\fR or
1160 \fIdemand\fR option has been specified, pppd will try to reopen the
1161 serial device and start another connection (after the holdoff period).
1162 Otherwise pppd will exit. If this signal is received during the
1163 holdoff period, it causes pppd to end the holdoff period immediately.
1166 This signal toggles the state of the \fIdebug\fR option.
1169 This signal causes pppd to renegotiate compression. This can be
1170 useful to re-enable compression after it has been disabled as a result
1171 of a fatal decompression error. (Fatal decompression errors generally
1172 indicate a bug in one or other implementation.)
1175 Paul Mackerras (Paul.Mackerras@cs.anu.edu.au), based on earlier work by
projects / ppp.git / blob