1 .\" manual page [] for pppd 2.3
2 .\" $FreeBSD: src/usr.sbin/pppd/pppd.8,v 1.20.2.4 2003/03/11 22:31:30 trhodes 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, providing that it is
46 supported by the serial device driver. Other systems
47 (e.g. SunOS, Linux) allow only a limited set of speeds.
49 .B active-filter \fIfilter-expression
50 Specifies a packet filter to be applied to data packets to determine
51 which packets are to be regarded as link activity, and therefore reset
52 the idle timer, or cause the link to be brought up in demand-dialling
53 mode. This option is useful in conjunction with the
54 \fBidle\fR option if there are packets being sent or received
55 regularly over the link (for example, routing information packets)
56 which would otherwise prevent the link from ever appearing to be idle.
57 The \fIfilter-expression\fR syntax is as described for tcpdump(1),
58 except that qualifiers which are inappropriate for a PPP link, such as
59 \fBether\fR and \fBarp\fR, are not permitted. Generally the filter
60 expression should be enclosed in single-quotes to prevent whitespace
61 in the expression from being interpreted by the shell.
64 if both the kernel and pppd were compiled with PPP_FILTER defined.
67 Set the async character map to <map>. This map describes which
68 control characters cannot be successfully received over the serial
69 line. Pppd will ask the peer to send these characters as a 2-byte
70 escape sequence. The argument is a 32 bit hex number with each bit
71 representing a character to escape. Bit 0 (00000001) represents the
72 character 0x00; bit 31 (80000000) represents the character 0x1f or ^_.
73 If multiple \fIasyncmap\fR options are given, the values are ORed
74 together. If no \fIasyncmap\fR option is given, no async character
75 map will be negotiated for the receive direction; the peer should then
76 escape \fIall\fR control characters. To escape transmitted
77 characters, use the \fIescape\fR option.
80 Require the peer to authenticate itself before allowing network
81 packets to be sent or received.
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.
96 .B connect-max-attempts \fI<n>
97 Attempt dial-out connection to remote system no more than specified number
98 of times (default = 1). If the connection is not made, pppd will exit.
99 Requires that \fBpersist\fR has been specified.
102 Use hardware flow control (i.e. RTS/CTS) to control the flow of data
103 on the serial port. If neither the \fIcrtscts\fR nor the
104 \fInocrtscts\fR option is given, the hardware flow control setting
105 for the serial port is left unchanged.
108 Add a default route to the system routing tables, using the peer as
109 the gateway, when IPCP negotiation is successfully completed.
110 This entry is removed when the PPP connection is broken. This option
111 is privileged if the \fInodefaultroute\fR option has been specified.
113 .B disconnect \fIscript
114 Run the executable or shell command specified by \fIscript\fR after
115 pppd has terminated the link. This script could, for example, issue
116 commands to the modem to cause it to hang up if hardware modem control
117 signals were not available. The disconnect script is not run if the
118 modem has already hung up. This option is privileged if the
119 \fInoauth\fR option is used.
121 .B escape \fIxx,yy,...
122 Specifies that certain characters should be escaped on transmission
123 (regardless of whether the peer requests them to be escaped with its
124 async control character map). The characters to be escaped are
125 specified as a list of hex numbers separated by commas. Note that
126 almost any character can be specified for the \fIescape\fR option,
127 unlike the \fIasyncmap\fR option which only allows control characters
128 to be specified. The characters which may not be escaped are those
129 with hex values 0x20 - 0x3f or 0x5e.
132 Read options from file \fIname\fR (the format is described below).
133 The file must be readable by the user who has invoked pppd.
136 Specifies that pppd should create a UUCP-style lock file for the
137 serial device to ensure exclusive access to the device.
140 Set the MRU [Maximum Receive Unit] value to \fIn\fR.
142 will ask the peer to send packets of no more than \fIn\fR bytes. The
143 minimum MRU value is 128. The default MRU value is 1500. A value of
144 296 is recommended for slow links (40 bytes for TCP/IP header + 256
148 Set the MTU [Maximum Transmit Unit] value to \fIn\fR. Unless the
149 peer requests a smaller value via MRU negotiation, pppd will
150 request that the kernel networking code send data packets of no more
151 than \fIn\fR bytes through the PPP network interface.
154 Enables the "passive" option in the LCP. With this option, pppd will
155 attempt to initiate a connection; if no reply is received from the
156 peer, pppd will then just wait passively for a valid LCP packet from
157 the peer, instead of exiting, as it would without this option.
160 .I <local_IP_address>\fB:\fI<remote_IP_address>
161 Set the local and/or remote interface IP addresses. Either one may be
162 omitted. The IP addresses can be specified with a host name or in
163 decimal dot notation (e.g. 150.234.56.78). The default local
164 address is the (first) IP address of the system (unless the
166 option is given). The remote address will be obtained from the peer
167 if not specified in any option. Thus, in simple cases, this option is
168 not required. If a local and/or remote IP address is specified with
170 will not accept a different value from the peer in the IPCP
171 negotiation, unless the \fIipcp-accept-local\fR and/or
172 \fIipcp-accept-remote\fR options are given, respectively.
175 Request that the peer compress packets that it sends, using the
176 BSD-Compress scheme, with a maximum code size of \fInr\fR bits, and
177 agree to compress packets sent to the peer with a maximum code size of
178 \fInt\fR bits. If \fInt\fR is not specified, it defaults to the value
179 given for \fInr\fR. Values in the range 9 to 15 may be used for
180 \fInr\fR and \fInt\fR; larger values give better compression but
181 consume more kernel memory for compression dictionaries.
182 Alternatively, a value of 0 for \fInr\fR or \fInt\fR disables
183 compression in the corresponding direction. Use \fInobsdcomp\fR or
184 \fIbsdcomp 0\fR to disable BSD-Compress compression entirely.
186 .B chap-interval \fIn
187 If this option is given, pppd will rechallenge the peer every \fIn\fR
190 .B chap-max-challenge \fIn
191 Set the maximum number of CHAP challenge transmissions to \fIn\fR
195 Set the CHAP restart interval (retransmission timeout for challenges)
196 to \fIn\fR seconds (default 3).
199 Enables connection debugging facilities.
200 If this option is given, pppd will log the contents of all
201 control packets sent or received in a readable form. The packets are
202 logged through syslog with facility \fIdaemon\fR and level
203 \fIdebug\fR. This information can be directed to a file by setting up
204 /etc/syslog.conf appropriately (see syslog.conf(5)).
207 Disable asyncmap negotiation, forcing all control characters to be
208 escaped for both the transmit and the receive direction.
211 Disable MRU [Maximum Receive Unit] negotiation. With this option,
212 pppd will use the default MRU value of 1500 bytes for both the
213 transmit and receive direction.
216 Request that the peer compress packets that it sends, using the
217 Deflate scheme, with a maximum window size of \fI2**nr\fR bytes, and
218 agree to compress packets sent to the peer with a maximum window size
219 of \fI2**nt\fR bytes. If \fInt\fR is not specified, it defaults to
220 the value given for \fInr\fR. Values in the range 8 to 15 may be used
221 for \fInr\fR and \fInt\fR; larger values give better compression but
222 consume more kernel memory for compression dictionaries.
223 Alternatively, a value of 0 for \fInr\fR or \fInt\fR disables
224 compression in the corresponding direction. Use \fInodeflate\fR or
225 \fIdeflate 0\fR to disable Deflate compression entirely. (Note: pppd
226 requests Deflate compression in preference to BSD-Compress if the peer
230 Initiate the link only on demand, i.e. when data traffic is present.
231 With this option, the remote IP address must be specified by the user
232 on the command line or in an options file. Pppd will initially
233 configure the interface and enable it for IP traffic without
234 connecting to the peer. When traffic is available, pppd will
235 connect to the peer and perform negotiation, authentication, etc.
236 When this is completed, pppd will commence passing data packets
237 (i.e., IP packets) across the link.
239 The \fIdemand\fR option implies the \fIpersist\fR option. If this
240 behaviour is not desired, use the \fInopersist\fR option after the
241 \fIdemand\fR option. The \fIidle\fR and \fIholdoff\fR
242 options are also useful in conjuction with the \fIdemand\fR option.
245 Append the domain name \fId\fR to the local host name for authentication
246 purposes. For example, if gethostname() returns the name porsche, but
247 the fully qualified domain name is porsche.Quotron.COM, you could
248 specify \fIdomain Quotron.COM\fR. Pppd would then use the name
249 \fIporsche.Quotron.COM\fR for looking up secrets in the secrets file,
250 and as the default name to send to the peer when authenticating itself
251 to the peer. This option is privileged.
254 Specifies how many seconds to wait before re-initiating the link after
255 it terminates. This option only has any effect if the \fIpersist\fR
256 or \fIdemand\fR option is used. The holdoff period is not applied if
257 the link was terminated because it was idle.
260 Specifies that pppd should disconnect if the link is idle for \fIn\fR
261 seconds. The link is idle when no data packets (i.e. IP packets) are
262 being sent or received. Note: it is not advisable to use this option
263 with the \fIpersist\fR option without the \fIdemand\fR option.
264 If the \fBactive-filter\fR
265 option is given, data packets which are rejected by the specified
266 activity filter also count as the link being idle.
269 With this option, pppd will accept the peer's idea of our local IP
270 address, even if the local IP address was specified in an option.
272 .B ipcp-accept-remote
273 With this option, pppd will accept the peer's idea of its (remote) IP
274 address, even if the remote IP address was specified in an option.
276 .B ipcp-max-configure \fIn
277 Set the maximum number of IPCP configure-request transmissions to
278 \fIn\fR (default 10).
280 .B ipcp-max-failure \fIn
281 Set the maximum number of IPCP configure-NAKs returned before starting
282 to send configure-Rejects instead to \fIn\fR (default 10).
284 .B ipcp-max-terminate \fIn
285 Set the maximum number of IPCP terminate-request transmissions to
289 Set the IPCP restart interval (retransmission timeout) to \fIn\fR
293 Provides an extra parameter to the ip-up and ip-down scripts. If this
294 option is given, the \fIstring\fR supplied is given as the 6th
295 parameter to those scripts.
298 Enable the IPXCP and IPX protocols. This option is presently only
299 supported under Linux, and only if your kernel has been configured to
303 Set the IPX network number in the IPXCP configure request frame to
304 \fIn\fR, a hexadecimal number (without a leading 0x). There is no
305 valid default. If this option is not specified, the network number is
306 obtained from the peer. If the peer does not have the network number,
307 the IPX protocol will not be started.
309 .B ipx-node \fIn\fB:\fIm
310 Set the IPX node numbers.
311 The two node numbers are separated from each
312 other with a colon character.
313 The first number \fIn\fR is the local
315 The second number \fIm\fR is the peer's node number.
317 node number is a hexadecimal number, at most 10 digits long.
319 numbers on the ipx-network must be unique.
322 If this option is not specified then the node numbers are
323 obtained from the peer.
325 .B ipx-router-name \fI<string>
326 Set the name of the router.
327 This is a string and is sent to the peer
331 Set the routing protocol to be received by this option.
333 instance of \fIipx-routing\fR may be specified.
335 option (0) may be specified as the only instance of ipx-routing.
337 values may be \fI0\fR for \fINONE\fR, \fI2\fR for \fIRIP/SAP\fR, and
338 \fI4\fR for \fINLSP\fR.
340 .B ipxcp-accept-local
341 Accept the peer's NAK for the node number specified in the ipx-node
343 If a node number was specified, and non-zero, the default is
344 to insist that the value be used.
345 If you include this option then you
346 will permit the peer to override the entry of the node number.
348 .B ipxcp-accept-network
349 Accept the peer's NAK for the network number specified in the
351 If a network number was specified, and non-zero, the
352 default is to insist that the value be used.
354 option then you will permit the peer to override the entry of the node
357 .B ipxcp-accept-remote
358 Use the peer's network number specified in the configure request
360 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.
369 .B ipxcp-max-failure \fIn
370 Set the maximum number of IPXCP NAK frames which the local system will
371 send before it rejects the options.
372 The default value is 3.
374 .B ipxcp-max-terminate \fIn
375 Set the maximum nuber of IPXCP terminate request frames before the
376 local system considers that the peer is not listening to them.
381 Enable debugging code in the kernel-level PPP driver. The argument
382 \fIn\fR is a number which is the sum of the following values: 1 to
383 enable general debug messages, 2 to request that the contents of
384 received packets be printed, and 4 to request that the contents of
385 transmitted packets be printed. On most systems, messages printed by
386 the kernel are logged by syslog(1) to a file as directed in the
387 /etc/syslog.conf configuration file.
389 .B lcp-echo-failure \fIn
390 If this option is given, pppd will presume the peer to be dead
391 if \fIn\fR LCP echo-requests are sent without receiving a valid LCP
392 echo-reply. If this happens, pppd will terminate the
393 connection. Use of this option requires a non-zero value for the
394 \fIlcp-echo-interval\fR parameter. This option can be used to enable
395 pppd to terminate after the physical connection has been broken
396 (e.g., the modem has hung up) in situations where no hardware modem
397 control lines are available.
399 .B lcp-echo-interval \fIn
400 If this option is given, pppd will send an LCP echo-request frame to
401 the peer every \fIn\fR seconds. Normally the peer should respond to
402 the echo-request by sending an echo-reply. This option can be used
403 with the \fIlcp-echo-failure\fR option to detect that the peer is no
406 .B lcp-max-configure \fIn
407 Set the maximum number of LCP configure-request transmissions to
408 \fIn\fR (default 10).
410 .B lcp-max-failure \fIn
411 Set the maximum number of LCP configure-NAKs returned before starting
412 to send configure-Rejects instead to \fIn\fR (default 10).
414 .B lcp-max-terminate \fIn
415 Set the maximum number of LCP terminate-request transmissions to
419 Set the LCP restart interval (retransmission timeout) to \fIn\fR
423 Don't use the modem control lines. With this option, pppd will ignore
424 the state of the CD (Carrier Detect) signal from the modem and will
425 not change the state of the DTR (Data Terminal Ready) signal.
428 Use the system password database for authenticating the peer using
429 PAP, and record the user in the system wtmp file. Note that the peer
430 must have an entry in the /etc/ppp/pap-secrets file as well as the
431 system password database to be allowed access.
434 Terminate the connection when it has been available for network
435 traffic for \fIn\fR seconds (i.e. \fIn\fR seconds after the first
436 network control protocol comes up).
439 Use the modem control lines. This option is the default. With this
440 option, pppd will wait for the CD (Carrier Detect) signal from the
441 modem to be asserted when opening the serial device (unless a connect
442 script is specified), and it will drop the DTR (Data Terminal Ready)
443 signal briefly when the connection is terminated and before executing
444 the connect script. On Ultrix, this option implies hardware flow
445 control, as for the \fIcrtscts\fR option.
448 If pppd is acting as a server for Microsoft Windows clients, this
449 option allows pppd to supply one or two DNS (Domain Name Server)
450 addresses to the clients. The first instance of this option specifies
451 the primary DNS address; the second instance (if given) specifies the
452 secondary DNS address. (This option was present in some older
453 versions of pppd under the name \fBdns-addr\fR.)
456 If pppd is acting as a server for Microsoft Windows or "Samba"
457 clients, this option allows pppd to supply one or two WINS (Windows
458 Internet Name Services) server addresses to the clients. The first
459 instance of this option specifies the primary WINS address; the second
460 instance (if given) specifies the secondary WINS address.
463 Set the name of the local system for authentication purposes to
464 \fIname\fR. This is a privileged option. With this option, pppd will
465 use lines in the secrets files which have \fIname\fR as the second
466 field when looking for a secret to use in authenticating the peer. In
467 addition, unless overridden with the \fIuser\fR option, \fIname\fR
468 will be used as the name to send to the peer when authenticating the
469 local system to the peer. (Note that pppd does not append the domain
473 Set the interface netmask to \fIn\fR, a 32 bit netmask in "decimal dot"
474 notation (e.g. 255.255.255.0). If this option is given, the value
475 specified is ORed with the default netmask. The default netmask is
476 chosen based on the negotiated remote IP address; it is the
477 appropriate network mask for the class of the remote IP address, ORed
478 with the netmasks for any non point-to-point network interfaces in the
479 system which are on the same network.
482 Disable Address/Control compression in both directions (send and
486 Do not require the peer to authenticate itself. This option is
487 privileged if the \fIauth\fR option is specified in /etc/ppp/options.
490 Disables BSD-Compress compression; \fBpppd\fR will not request or
491 agree to compress packets using the BSD-Compress scheme.
494 Disable CCP (Compression Control Protocol) negotiation. This option
495 should only be required if the peer is buggy and gets confused by
496 requests from pppd for CCP negotiation.
499 Disable hardware flow control (i.e. RTS/CTS) on the serial port. If
500 neither the \fIcrtscts\fR nor the \fInocrtscts\fR option is given,
501 the hardware flow control setting for the serial port is left
505 Disable the \fIdefaultroute\fR option. The system administrator who
506 wishes to prevent users from creating default routes with pppd
507 can do so by placing this option in the /etc/ppp/options file.
510 Disables Deflate compression; pppd will not request or agree to
511 compress packets using the Deflate scheme.
514 Don't detach from the controlling terminal. Without this option, if a
515 serial device other than the terminal on the standard input is
516 specified, pppd will fork to become a background process.
519 Disable IPCP negotiation and IP communication. This option should
520 only be required if the peer is buggy and gets confused by requests
521 from pppd for IPCP negotiation.
524 Disables the default behaviour when no local IP address is specified,
525 which is to determine (if possible) the local IP address from the
526 hostname. With this option, the peer will have to supply the local IP
527 address during IPCP negotiation (unless it specified explicitly on the
528 command line or in an options file).
531 Disable the IPXCP and IPX protocols. This option should only be
532 required if the peer is buggy and gets confused by requests from pppd
533 for IPXCP negotiation.
536 Disable magic number negotiation. With this option, pppd cannot
537 detect a looped-back line. This option should only be needed if the
541 Disable protocol field compression negotiation in both the receive and
542 the transmit direction.
545 Exit once a connection has been made and terminated. This is the
546 default unless the \fIpersist\fR or \fIdemand\fR option has been
550 Do not accept or agree to Predictor-1 compression.
553 Disable the \fIproxyarp\fR option. The system administrator who
554 wishes to prevent users from creating proxy ARP entries with pppd can
555 do so by placing this option in the /etc/ppp/options file.
558 Disable Van Jacobson style TCP/IP header compression in both the
559 transmit and the receive direction.
562 Disable the connection-ID compression option in Van Jacobson style
563 TCP/IP header compression. With this option, pppd will not omit the
564 connection-ID byte from Van Jacobson compressed TCP/IP headers, nor
565 ask the peer to do so.
568 Indicates that all secrets in the /etc/ppp/pap-secrets file which are
569 used for checking the identity of the peer are encrypted, and thus
570 pppd should not accept a password which, before encryption, is
571 identical to the secret from the /etc/ppp/pap-secrets file.
573 .B pap-max-authreq \fIn
574 Set the maximum number of PAP authenticate-request transmissions to
575 \fIn\fR (default 10).
578 Set the PAP restart interval (retransmission timeout) to \fIn\fR
582 Set the maximum time that pppd will wait for the peer to authenticate
583 itself with PAP to \fIn\fR seconds (0 means no limit).
585 .B pass-filter \fIfilter-expression
586 Specifies a packet filter to applied to data packets being sent or
587 received to determine which packets should be allowed to pass.
588 Packets which are rejected by the filter are silently discarded. This
589 option can be used to prevent specific network daemons (such as
590 routed) using up link bandwidth, or to provide a basic firewall
592 The \fIfilter-expression\fR syntax is as described for tcpdump(1),
593 except that qualifiers which are inappropriate for a PPP link, such as
594 \fBether\fR and \fBarp\fR, are not permitted. Generally the filter
595 expression should be enclosed in single-quotes to prevent whitespace
596 in the expression from being interpreted by the shell. Note that it
597 is possible to apply different constraints to incoming and outgoing
598 packets using the \fBinbound\fR and \fBoutbound\fR qualifiers.
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).
650 Sets the name used for authenticating the local system to the peer to
654 Sets the number of connection slots to be used by the Van Jacobson
655 TCP/IP header compression and decompression code to \fIn\fR, which
656 must be between 2 and 16 (inclusive).
659 Run the executable or shell command specified by \fIscript\fR before
660 initiating PPP negotiation, after the connect script (if any) has
661 completed. This option is privileged if the \fInoauth\fR option is
665 Use software flow control (i.e. XON/XOFF) to control the flow of data on
668 Options can be taken from files as well as the command line. Pppd
669 reads options from the files /etc/ppp/options, ~/.ppprc and
670 /etc/ppp/options.\fIttyname\fR (in that order) before processing the
671 options on the command line. (In fact, the command-line options are
672 scanned to find the terminal name before the options.\fIttyname\fR
673 file is read.) In forming the name of the options.\fIttyname\fR file,
674 the initial /dev/ is removed from the terminal name, and any remaining
675 / characters are replaced with dots.
677 An options file is parsed into a series of words, delimited by
678 whitespace. Whitespace can be included in a word by enclosing the
679 word in double-quotes ("). A backslash (\\) quotes the following character.
680 A hash (#) starts a comment, which continues until the end of the
681 line. There is no restriction on using the \fIfile\fR or \fIcall\fR
682 options within an options file.
685 provides system administrators with sufficient access control that PPP
686 access to a server machine can be provided to legitimate users without
687 fear of compromising the security of the server or the network it's
688 on. In part this is provided by the /etc/ppp/options file, where the
689 administrator can place options to restrict the ways in which pppd can
690 be used, and in part by the PAP and CHAP secrets files, where the
691 administrator can restrict the set of IP addresses which individual
694 The normal way that pppd should be set up is to have the \fIauth\fR
695 option in the /etc/ppp/options file. (This may become the default in
696 later releases.) If users wish to use pppd to dial out to a peer
697 which will refuse to authenticate itself (such as an internet service
698 provider), the system administrator should create an options file
699 under /etc/ppp/peers containing the \fInoauth\fR option, the name of
700 the serial port to use, and the \fIconnect\fR option (if required),
701 plus any other appropriate options. In this way, pppd can be set up
702 to allow non-privileged users to make unauthenticated connections only
705 As indicated above, some security-sensitive options are privileged,
706 which means that they may not be used by an ordinary non-privileged
707 user running a setuid-root pppd, either on the command line, in the
708 user's ~/.ppprc file, or in an options file read using the \fIfile\fR
709 option. Privileged options may be used in /etc/ppp/options file or in
710 an options file read using the \fIcall\fR option. If pppd is being
711 run by the root user, privileged options can be used without
714 Authentication is the process whereby one peer convinces the other of
715 its identity. This involves the first peer sending its name to the
716 other, together with some kind of secret information which could only
717 come from the genuine authorized user of that name. In such an
718 exchange, we will call the first peer the "client" and the other the
719 "server". The client has a name by which it identifies itself to the
720 server, and the server also has a name by which it identifies itself
721 to the client. Generally the genuine client shares some secret (or
722 password) with the server, and authenticates itself by proving that it
723 knows that secret. Very often, the names used for authentication
724 correspond to the internet hostnames of the peers, but this is not
727 At present, pppd supports two authentication protocols: the Password
728 Authentication Protocol (PAP) and the Challenge Handshake
729 Authentication Protocol (CHAP). PAP involves the client sending its
730 name and a cleartext password to the server to authenticate itself.
731 In contrast, the server initiates the CHAP authentication exchange by
732 sending a challenge to the client (the challenge packet includes the
733 server's name). The client must respond with a response which
734 includes its name plus a hash value derived from the shared secret and
735 the challenge, in order to prove that it knows the secret.
737 The PPP protocol, being symmetrical, allows both peers to require the
738 other to authenticate itself. In that case, two separate and
739 independent authentication exchanges will occur. The two exchanges
740 could use different authentication protocols, and in principle,
741 different names could be used in the two exchanges.
743 The default behaviour of pppd is to agree to authenticate if
744 requested, and to not require authentication from the peer. However,
745 pppd will not agree to authenticate itself with a particular protocol
746 if it has no secrets which could be used to do so.
748 Pppd stores secrets for use in authentication in secrets
749 files (/etc/ppp/pap-secrets for PAP, /etc/ppp/chap-secrets for CHAP).
750 Both secrets files have the same format. The secrets files can
751 contain secrets for pppd to use in authenticating itself to other
752 systems, as well as secrets for pppd to use when authenticating other
755 Each line in a secrets file contains one secret. A given secret is
756 specific to a particular combination of client and server - it can
757 only be used by that client to authenticate itself to that server.
758 Thus each line in a secrets file has at least 3 fields: the name of
759 the client, the name of the server, and the secret. These fields may
760 be followed by a list of the IP addresses that the specified client
761 may use when connecting to the specified server.
763 A secrets file is parsed into words as for an options file, so the
764 client name, server name and secrets fields must each be one word,
765 with any embedded spaces or other special characters quoted or
766 escaped. Any following words on the same line are taken to be a list
767 of acceptable IP addresses for that client, or an
768 override for "local:remote" addresses (the same format used on the
769 command line or in the options file) when on a line that contains a
770 specific client name (not a wildcard nor empty).
771 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 Additional checks are performed when the \fBlogin\fR option is used.
830 If the file /etc/ppp/ppp.deny exists, and the user is listed in it,
831 the authentication fails. If the file /etc/ppp/ppp.shells exists and
832 the user's normal login shell is not listed, the authentication fails.
834 Authentication must be satisfactorily completed before IPCP (or any
835 other Network Control Protocol) can be started. If the peer is
836 required to authenticate itself, and fails to do so, pppd will
837 terminated the link (by closing LCP). If IPCP negotiates an
838 unacceptable IP address for the remote host, IPCP will be closed. IP
839 packets can only be sent or received when IPCP is open.
841 In some cases it is desirable to allow some hosts which can't
842 authenticate themselves to connect and use one of a restricted set of
843 IP addresses, even when the local host generally requires
844 authentication. If the peer refuses to authenticate itself when
845 requested, pppd takes that as equivalent to authenticating with PAP
846 using the empty string for the username and password. Thus, by adding
847 a line to the pap-secrets file which specifies the empty string for
848 the client and password, it is possible to allow restricted access to
849 hosts which refuse to authenticate themselves.
852 When IPCP negotiation is completed successfully, pppd will inform the
853 kernel of the local and remote IP addresses for the ppp interface.
854 This is sufficient to create a host route to the remote end of the
855 link, which will enable the peers to exchange IP packets.
856 Communication with other machines generally requires further
857 modification to routing tables and/or ARP (Address Resolution
858 Protocol) tables. In most cases the \fIdefaultroute\fR and/or
859 \fIproxyarp\fR options are sufficient for this, but in some cases
860 further intervention is required. The /etc/ppp/ip-up script can be
863 Sometimes it is desirable to add a default route through the remote
864 host, as in the case of a machine whose only connection to the
865 Internet is through the ppp interface. The \fIdefaultroute\fR option
866 causes pppd to create such a default route when IPCP comes up, and
867 delete it when the link is terminated.
869 In some cases it is desirable to use proxy ARP, for example on a
870 server machine connected to a LAN, in order to allow other hosts to
871 communicate with the remote host. The \fIproxyarp\fR option causes
872 pppd to look for a network interface on the same subnet as the remote
873 host (an interface supporting broadcast and ARP, which is up and not a
874 point-to-point or loopback interface). If found, pppd creates a
875 permanent, published ARP entry with the IP address of the remote host
876 and the hardware address of the network interface found.
878 When the \fIdemand\fR option is used, the interface IP addresses have
879 already been set at the point when IPCP comes up. If pppd has not
880 been able to negotiate the same addresses that it used to configure
881 the interface (for example when the peer is an ISP that uses dynamic
882 IP address assignment), pppd has to change the interface IP addresses
883 to the negotiated addresses. This may disrupt existing connections,
884 and the use of demand dialling with peers that do dynamic IP address
885 assignment is not recommended.
888 The following examples assume that the /etc/ppp/options file contains
889 the \fIauth\fR option (as in the default /etc/ppp/options file in the
892 Probably the most common use of pppd is to dial out to an ISP. This
893 can be done with a command such as
897 where the /etc/ppp/peers/isp file is set up by the system
898 administrator to contain something like this:
902 connect '/usr/sbin/chat -v -f /etc/ppp/chat-isp'
906 In this example, we are using chat to dial the ISP's modem and go
907 through any logon sequence required. The /etc/ppp/chat-isp file
908 contains the script used by chat; it could for example contain
921 ABORT "Username/Password Incorrect"
931 "word:" "\\qmypassword"
937 See the chat(8) man page for details of chat scripts.
939 Pppd can also be used to provide a dial-in ppp service for users. If
940 the users already have login accounts, the simplest way to set up the
941 ppp service is to let the users log in to their accounts and run pppd
942 (installed setuid-root) with a command such as
946 To allow a user to use the PPP facilities, you need to allocate an IP
947 address for that user's machine and create an entry in
948 /etc/ppp/pap-secrets or /etc/ppp/chap-secrets (depending on which
949 authentication method the PPP implementation on the user's machine
950 supports), so that the user's
951 machine can authenticate itself. For example, if Joe has a machine
952 called "joespc" which is to be allowed to dial in to the machine
953 called "server" and use the IP address joespc.my.net, you would add an
954 entry like this to /etc/ppp/pap-secrets or /etc/ppp/chap-secrets:
956 joespc server "joe's secret" joespc.my.net
958 Alternatively, you can create a username called (for example) "ppp",
959 whose login shell is pppd and whose home directory is /etc/ppp.
960 Options to be used when pppd is run this way can be put in
963 If your serial connection is any more complicated than a piece of
964 wire, you may need to arrange for some control characters to be
965 escaped. In particular, it is often useful to escape XON (^Q) and
966 XOFF (^S), using \fIasyncmap a0000\fR. If the path includes a telnet,
967 you probably should escape ^] as well (\fIasyncmap 200a0000\fR). If
968 the path includes an rlogin, you will need to use the \fIescape ff\fR
969 option on the end which is running the rlogin client, since many
970 rlogin implementations are not transparent; they will remove the
971 sequence [0xff, 0xff, 0x73, 0x73, followed by any 8 bytes] from the
975 Messages are sent to the syslog daemon using facility LOG_DAEMON.
976 (This can be overriden by recompiling pppd with the macro
977 LOG_PPP defined as the desired facility.) In order to see the error
978 and debug messages, you will need to edit your /etc/syslog.conf file
979 to direct the messages to the desired output device or file.
981 The \fIdebug\fR option causes the contents of all control packets sent
982 or received to be logged, that is, all LCP, PAP, CHAP or IPCP packets.
983 This can be useful if the PPP negotiation does not succeed or if
984 authentication fails.
985 If debugging is enabled at compile time, the \fIdebug\fR option also
986 causes other debugging messages to be logged.
988 Debugging can also be enabled or disabled by sending a SIGUSR1 signal
989 to the pppd process. This signal acts as a toggle.
991 Pppd invokes scripts at various stages in its processing which can be
992 used to perform site-specific ancillary processing. These scripts are
993 usually shell scripts, but could be executable code files instead.
994 Pppd does not wait for the scripts to finish. The scripts are
995 executed as root (with the real and effective user-id set to 0), so
996 that they can do things such as update routing tables or run
997 privileged daemons. Be careful that the contents of these scripts do
998 not compromise your system's security. Pppd runs the scripts with
999 standard input, output and error redirected to /dev/null, and with an
1000 environment that is empty except for some environment variables that
1001 give information about the link. The environment variables that pppd
1005 The name of the serial tty device being used.
1008 The name of the network interface being used.
1011 The IP address for the local end of the link. This is only set when
1015 The IP address for the remote end of the link. This is only set when
1019 The authenticated name of the peer. This is only set if the peer
1020 authenticates itself.
1023 The baud rate of the tty device.
1026 The real user-id of the user who invoked pppd.
1028 Pppd invokes the following scripts, if they exist. It is not an error
1029 if they don't exist.
1032 A program or script which is executed after the remote system
1033 successfully authenticates itself. It is executed with the parameters
1035 \fIinterface-name peer-name user-name tty-device speed\fR
1037 Note that this script is not executed if the peer doesn't authenticate
1038 itself, for example when the \fInoauth\fR option is used.
1040 .B /etc/ppp/auth-down
1041 A program or script which is executed when the link goes down, if
1042 /etc/ppp/auth-up was previously executed. It is executed in the same
1043 manner with the same parameters as /etc/ppp/auth-up.
1046 A program or script which is executed when the link is available for
1047 sending and receiving IP packets (that is, IPCP has come up). It is
1048 executed with the parameters
1050 \fIinterface-name tty-device speed local-IP-address
1051 remote-IP-address ipparam\fR
1054 A program or script which is executed when the link is no longer
1055 available for sending and receiving IP packets. This script can be
1056 used for undoing the effects of the /etc/ppp/ip-up script. It is
1057 invoked in the same manner and with the same parameters as the ip-up
1061 A program or script which is executed when the link is available for
1062 sending and receiving IPX packets (that is, IPXCP has come up). It is
1063 executed with the parameters
1065 \fIinterface-name tty-device speed network-number local-IPX-node-address
1066 remote-IPX-node-address local-IPX-routing-protocol remote-IPX-routing-protocol
1067 local-IPX-router-name remote-IPX-router-name ipparam pppd-pid\fR
1069 The local-IPX-routing-protocol and remote-IPX-routing-protocol field
1070 may be one of the following:
1072 NONE to indicate that there is no routing protocol
1074 RIP to indicate that RIP/SAP should be used
1076 NLSP to indicate that Novell NLSP should be used
1078 RIP NLSP to indicate that both RIP/SAP and NLSP should be used
1080 .B /etc/ppp/ipx-down
1081 A program or script which is executed when the link is no longer
1082 available for sending and receiving IPX packets. This script can be
1083 used for undoing the effects of the /etc/ppp/ipx-up script. It is
1084 invoked in the same manner and with the same parameters as the ipx-up
1088 .B /var/run/ppp\fIn\fB.pid \fR(BSD or Linux), \fB/etc/ppp/ppp\fIn\fB.pid \fR(others)
1089 Process-ID for pppd process on ppp interface unit \fIn\fR.
1091 .B /etc/ppp/pap-secrets
1092 Usernames, passwords and IP addresses for PAP authentication. This
1093 file should be owned by root and not readable or writable by any other
1094 user. Pppd will log a warning if this is not the case.
1096 .B /etc/ppp/chap-secrets
1097 Names, secrets and IP addresses for CHAP authentication. As for
1098 /etc/ppp/pap-secrets, this file should be owned by root and not
1099 readable or writable by any other user. Pppd will log a warning if
1100 this is not the case.
1103 System default options for pppd, read before user default options or
1104 command-line options.
1107 User default options, read before /etc/ppp/options.\fIttyname\fR.
1109 .B /etc/ppp/options.\fIttyname
1110 System default options for the serial port being used, read after
1111 ~/.ppprc. In forming the \fIttyname\fR part of this
1112 filename, an initial /dev/ is stripped from the port name (if
1113 present), and any slashes in the remaining part are converted to
1117 A directory containing options files which may contain privileged
1118 options, even if pppd was invoked by a user other than root. The
1119 system administrator can create options files in this directory to
1120 permit non-privileged users to dial out without requiring the peer to
1121 authenticate, but only to certain trusted peers.
1123 .B /etc/ppp/ppp.deny
1124 Lists users who may not use the system password PAP authentication.
1126 .B /etc/ppp/ppp.shells
1127 Lists user shells which are approved for system password PAP authentication
1130 .B /usr/share/examples/pppd/
1131 Sample pppd configuration files.
1138 \fICompressing TCP/IP headers for low-speed serial links.\fR
1143 .I The MD5 Message-Digest Algorithm.
1148 .I PPP Internet Protocol Control Protocol (IPCP).
1152 Lloyd, B.; Simpson, W.A.
1153 .I PPP authentication protocols.
1158 .I The Point\-to\-Point Protocol (PPP).
1163 .I PPP in HDLC-like Framing.
1166 The following signals have the specified effect when sent to pppd.
1169 These signals cause pppd to terminate the link (by closing LCP),
1170 restore the serial device settings, and exit.
1173 This signal causes pppd to terminate the link, restore the serial
1174 device settings, and close the serial device. If the \fIpersist\fR or
1175 \fIdemand\fR option has been specified, pppd will try to reopen the
1176 serial device and start another connection (after the holdoff period).
1177 Otherwise pppd will exit. If this signal is received during the
1178 holdoff period, it causes pppd to end the holdoff period immediately.
1181 This signal toggles the state of the \fIdebug\fR option.
1184 This signal causes pppd to renegotiate compression. This can be
1185 useful to re-enable compression after it has been disabled as a result
1186 of a fatal decompression error. (Fatal decompression errors generally
1187 indicate a bug in one or other implementation.)
1190 Paul Mackerras (Paul.Mackerras@cs.anu.edu.au), based on earlier work by
alexh's projects / dragonfly.git / blob