1 .\" manual page [] for pppd 2.3
4 .\" SS subsection heading
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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 callback \fIphone_number
187 Request a call-back to the \fIphone_number\fR. This only works if the peer
188 is speaking the Call Back Configuration Protocol. Do not put this into the
189 main options file if you sometimes connect to servers that don't support
192 .B chap-interval \fIn
193 If this option is given, pppd will rechallenge the peer every \fIn\fR
196 .B chap-max-challenge \fIn
197 Set the maximum number of CHAP challenge transmissions to \fIn\fR
201 Set the CHAP restart interval (retransmission timeout for challenges)
202 to \fIn\fR seconds (default 3).
205 Enables connection debugging facilities.
206 If this option is given, pppd will log the contents of all
207 control packets sent or received in a readable form. The packets are
208 logged through syslog with facility \fIdaemon\fR and level
209 \fIdebug\fR. This information can be directed to a file by setting up
210 /etc/syslog.conf appropriately (see syslog.conf(5)).
213 Disable asyncmap negotiation, forcing all control characters to be
214 escaped for both the transmit and the receive direction.
217 Disable MRU [Maximum Receive Unit] negotiation. With this option,
218 pppd will use the default MRU value of 1500 bytes for both the
219 transmit and receive direction.
222 Request that the peer compress packets that it sends, using the
223 Deflate scheme, with a maximum window size of \fI2**nr\fR bytes, and
224 agree to compress packets sent to the peer with a maximum window size
225 of \fI2**nt\fR bytes. If \fInt\fR is not specified, it defaults to
226 the value given for \fInr\fR. Values in the range 8 to 15 may be used
227 for \fInr\fR and \fInt\fR; larger values give better compression but
228 consume more kernel memory for compression dictionaries.
229 Alternatively, a value of 0 for \fInr\fR or \fInt\fR disables
230 compression in the corresponding direction. Use \fInodeflate\fR or
231 \fIdeflate 0\fR to disable Deflate compression entirely. (Note: pppd
232 requests Deflate compression in preference to BSD-Compress if the peer
236 Initiate the link only on demand, i.e. when data traffic is present.
237 With this option, the remote IP address must be specified by the user
238 on the command line or in an options file. Pppd will initially
239 configure the interface and enable it for IP traffic without
240 connecting to the peer. When traffic is available, pppd will
241 connect to the peer and perform negotiation, authentication, etc.
242 When this is completed, pppd will commence passing data packets
243 (i.e., IP packets) across the link.
245 The \fIdemand\fR option implies the \fIpersist\fR option. If this
246 behaviour is not desired, use the \fInopersist\fR option after the
247 \fIdemand\fR option. The \fIidle\fR and \fIholdoff\fR
248 options are also useful in conjunction with the \fIdemand\fR option.
251 Append the domain name \fId\fR to the local host name for authentication
252 purposes. For example, if gethostname() returns the name porsche, but
253 the fully qualified domain name is porsche.Quotron.COM, you could
254 specify \fIdomain Quotron.COM\fR. Pppd would then use the name
255 \fIporsche.Quotron.COM\fR for looking up secrets in the secrets file,
256 and as the default name to send to the peer when authenticating itself
257 to the peer. This option is privileged.
260 Specifies how many seconds to wait before re-initiating the link after
261 it terminates. This option only has any effect if the \fIpersist\fR
262 or \fIdemand\fR option is used. The holdoff period is not applied if
263 the link was terminated because it was idle.
266 Specifies that pppd should disconnect if the link is idle for \fIn\fR
267 seconds. The link is idle when no data packets (i.e. IP packets) are
268 being sent or received. Note: it is not advisable to use this option
269 with the \fIpersist\fR option without the \fIdemand\fR option.
270 If the \fBactive-filter\fR
271 option is given, data packets which are rejected by the specified
272 activity filter also count as the link being idle.
275 With this option, pppd will accept the peer's idea of our local IP
276 address, even if the local IP address was specified in an option.
278 .B ipcp-accept-remote
279 With this option, pppd will accept the peer's idea of its (remote) IP
280 address, even if the remote IP address was specified in an option.
282 .B ipcp-max-configure \fIn
283 Set the maximum number of IPCP configure-request transmissions to
284 \fIn\fR (default 10).
286 .B ipcp-max-failure \fIn
287 Set the maximum number of IPCP configure-NAKs returned before starting
288 to send configure-Rejects instead to \fIn\fR (default 10).
290 .B ipcp-max-terminate \fIn
291 Set the maximum number of IPCP terminate-request transmissions to
295 Set the IPCP restart interval (retransmission timeout) to \fIn\fR
299 Provides an extra parameter to the ip-up and ip-down scripts. If this
300 option is given, the \fIstring\fR supplied is given as the 6th
301 parameter to those scripts.
304 Enable the IPXCP and IPX protocols. This option is presently only
305 supported under Linux, and only if your kernel has been configured to
309 Set the IPX network number in the IPXCP configure request frame to
310 \fIn\fR, a hexadecimal number (without a leading 0x). There is no
311 valid default. If this option is not specified, the network number is
312 obtained from the peer. If the peer does not have the network number,
313 the IPX protocol will not be started.
315 .B ipx-node \fIn\fB:\fIm
316 Set the IPX node numbers.
317 The two node numbers are separated from each
318 other with a colon character.
319 The first number \fIn\fR is the local
321 The second number \fIm\fR is the peer's node number.
323 node number is a hexadecimal number, at most 10 digits long.
325 numbers on the ipx-network must be unique.
328 If this option is not specified then the node numbers are
329 obtained from the peer.
331 .B ipx-router-name \fI<string>
332 Set the name of the router.
333 This is a string and is sent to the peer
337 Set the routing protocol to be received by this option.
339 instance of \fIipx-routing\fR may be specified.
341 option (0) may be specified as the only instance of ipx-routing.
343 values may be \fI0\fR for \fINONE\fR, \fI2\fR for \fIRIP/SAP\fR, and
344 \fI4\fR for \fINLSP\fR.
346 .B ipxcp-accept-local
347 Accept the peer's NAK for the node number specified in the ipx-node
349 If a node number was specified, and non-zero, the default is
350 to insist that the value be used.
351 If you include this option then you
352 will permit the peer to override the entry of the node number.
354 .B ipxcp-accept-network
355 Accept the peer's NAK for the network number specified in the
357 If a network number was specified, and non-zero, the
358 default is to insist that the value be used.
360 option then you will permit the peer to override the entry of the node
363 .B ipxcp-accept-remote
364 Use the peer's network number specified in the configure request
366 If a node number was specified for the peer and this option was
367 not specified, the peer will be forced to use the value which you have
370 .B ipxcp-max-configure \fIn
371 Set the maximum number of IPXCP configure request frames which the
372 system will send to \fIn\fR.
375 .B ipxcp-max-failure \fIn
376 Set the maximum number of IPXCP NAK frames which the local system will
377 send before it rejects the options.
378 The default value is 3.
380 .B ipxcp-max-terminate \fIn
381 Set the maximum number of IPXCP terminate request frames before the
382 local system considers that the peer is not listening to them.
387 Enable debugging code in the kernel-level PPP driver. The argument
388 \fIn\fR is a number which is the sum of the following values: 1 to
389 enable general debug messages, 2 to request that the contents of
390 received packets be printed, and 4 to request that the contents of
391 transmitted packets be printed. On most systems, messages printed by
392 the kernel are logged by syslog(1) to a file as directed in the
393 /etc/syslog.conf configuration file.
395 .B lcp-echo-failure \fIn
396 If this option is given, pppd will presume the peer to be dead
397 if \fIn\fR LCP echo-requests are sent without receiving a valid LCP
398 echo-reply. If this happens, pppd will terminate the
399 connection. Use of this option requires a non-zero value for the
400 \fIlcp-echo-interval\fR parameter. This option can be used to enable
401 pppd to terminate after the physical connection has been broken
402 (e.g., the modem has hung up) in situations where no hardware modem
403 control lines are available.
405 .B lcp-echo-interval \fIn
406 If this option is given, pppd will send an LCP echo-request frame to
407 the peer every \fIn\fR seconds. Normally the peer should respond to
408 the echo-request by sending an echo-reply. This option can be used
409 with the \fIlcp-echo-failure\fR option to detect that the peer is no
412 .B lcp-max-configure \fIn
413 Set the maximum number of LCP configure-request transmissions to
414 \fIn\fR (default 10).
416 .B lcp-max-failure \fIn
417 Set the maximum number of LCP configure-NAKs returned before starting
418 to send configure-Rejects instead to \fIn\fR (default 10).
420 .B lcp-max-terminate \fIn
421 Set the maximum number of LCP terminate-request transmissions to
425 Set the LCP restart interval (retransmission timeout) to \fIn\fR
429 Don't use the modem control lines. With this option, pppd will ignore
430 the state of the CD (Carrier Detect) signal from the modem and will
431 not change the state of the DTR (Data Terminal Ready) signal.
434 Use the system password database for authenticating the peer using
435 PAP, and record the user in the system wtmp file. Note that the peer
436 must have an entry in the /etc/ppp/pap-secrets file as well as the
437 system password database to be allowed access.
440 Terminate the connection when it has been available for network
441 traffic for \fIn\fR seconds (i.e. \fIn\fR seconds after the first
442 network control protocol comes up).
445 Use the modem control lines. This option is the default. With this
446 option, pppd will wait for the CD (Carrier Detect) signal from the
447 modem to be asserted when opening the serial device (unless a connect
448 script is specified), and it will drop the DTR (Data Terminal Ready)
449 signal briefly when the connection is terminated and before executing
450 the connect script. On Ultrix, this option implies hardware flow
451 control, as for the \fIcrtscts\fR option.
454 If pppd is acting as a server for Microsoft Windows clients, this
455 option allows pppd to supply one or two DNS (Domain Name Server)
456 addresses to the clients. The first instance of this option specifies
457 the primary DNS address; the second instance (if given) specifies the
458 secondary DNS address. (This option was present in some older
459 versions of pppd under the name \fBdns-addr\fR.)
462 If pppd is acting as a server for Microsoft Windows or "Samba"
463 clients, this option allows pppd to supply one or two WINS (Windows
464 Internet Name Services) server addresses to the clients. The first
465 instance of this option specifies the primary WINS address; the second
466 instance (if given) specifies the secondary WINS address.
469 Set the name of the local system for authentication purposes to
470 \fIname\fR. This is a privileged option. With this option, pppd will
471 use lines in the secrets files which have \fIname\fR as the second
472 field when looking for a secret to use in authenticating the peer. In
473 addition, unless overridden with the \fIuser\fR option, \fIname\fR
474 will be used as the name to send to the peer when authenticating the
475 local system to the peer. (Note that pppd does not append the domain
479 Set the interface netmask to \fIn\fR, a 32 bit netmask in "decimal dot"
480 notation (e.g. 255.255.255.0). If this option is given, the value
481 specified is ORed with the default netmask. The default netmask is
482 chosen based on the negotiated remote IP address; it is the
483 appropriate network mask for the class of the remote IP address, ORed
484 with the netmasks for any non point-to-point network interfaces in the
485 system which are on the same network.
488 Disable Address/Control compression in both directions (send and
492 Do not require the peer to authenticate itself. This option is
493 privileged if the \fIauth\fR option is specified in /etc/ppp/options.
496 Disables BSD-Compress compression; \fBpppd\fR will not request or
497 agree to compress packets using the BSD-Compress scheme.
500 Disable CCP (Compression Control Protocol) negotiation. This option
501 should only be required if the peer is buggy and gets confused by
502 requests from pppd for CCP negotiation.
505 Disable hardware flow control (i.e. RTS/CTS) on the serial port. If
506 neither the \fIcrtscts\fR nor the \fInocrtscts\fR option is given,
507 the hardware flow control setting for the serial port is left
511 Disable the \fIdefaultroute\fR option. The system administrator who
512 wishes to prevent users from creating default routes with pppd
513 can do so by placing this option in the /etc/ppp/options file.
516 Disables Deflate compression; pppd will not request or agree to
517 compress packets using the Deflate scheme.
520 Don't detach from the controlling terminal. Without this option, if a
521 serial device other than the terminal on the standard input is
522 specified, pppd will fork to become a background process.
525 Disable IPCP negotiation and IP communication. This option should
526 only be required if the peer is buggy and gets confused by requests
527 from pppd for IPCP negotiation.
530 Disables the default behaviour when no local IP address is specified,
531 which is to determine (if possible) the local IP address from the
532 hostname. With this option, the peer will have to supply the local IP
533 address during IPCP negotiation (unless it specified explicitly on the
534 command line or in an options file).
537 Disable the IPXCP and IPX protocols. This option should only be
538 required if the peer is buggy and gets confused by requests from pppd
539 for IPXCP negotiation.
542 Disable magic number negotiation. With this option, pppd cannot
543 detect a looped-back line. This option should only be needed if the
547 Disable protocol field compression negotiation in both the receive and
548 the transmit direction.
551 Exit once a connection has been made and terminated. This is the
552 default unless the \fIpersist\fR or \fIdemand\fR option has been
556 Do not accept or agree to Predictor-1 compression.
559 Disable the \fIproxyarp\fR option. The system administrator who
560 wishes to prevent users from creating proxy ARP entries with pppd can
561 do so by placing this option in the /etc/ppp/options file.
564 Disable Van Jacobson style TCP/IP header compression in both the
565 transmit and the receive direction.
568 Disable the connection-ID compression option in Van Jacobson style
569 TCP/IP header compression. With this option, pppd will not omit the
570 connection-ID byte from Van Jacobson compressed TCP/IP headers, nor
571 ask the peer to do so.
574 Indicates that all secrets in the /etc/ppp/pap-secrets file which are
575 used for checking the identity of the peer are encrypted, and thus
576 pppd should not accept a password which, before encryption, is
577 identical to the secret from the /etc/ppp/pap-secrets file.
579 .B pap-max-authreq \fIn
580 Set the maximum number of PAP authenticate-request transmissions to
581 \fIn\fR (default 10).
584 Set the PAP restart interval (retransmission timeout) to \fIn\fR
588 Set the maximum time that pppd will wait for the peer to authenticate
589 itself with PAP to \fIn\fR seconds (0 means no limit).
591 .B pass-filter \fIfilter-expression
592 Specifies a packet filter to applied to data packets being sent or
593 received to determine which packets should be allowed to pass.
594 Packets which are rejected by the filter are silently discarded. This
595 option can be used to prevent specific network daemons (such as
596 routed) using up link bandwidth, or to provide a basic firewall
598 The \fIfilter-expression\fR syntax is as described for tcpdump(1),
599 except that qualifiers which are inappropriate for a PPP link, such as
600 \fBether\fR and \fBarp\fR, are not permitted. Generally the filter
601 expression should be enclosed in single-quotes to prevent whitespace
602 in the expression from being interpreted by the shell. Note that it
603 is possible to apply different constraints to incoming and outgoing
604 packets using the \fBinbound\fR and \fBoutbound\fR qualifiers.
606 option is currently only available under NetBSD, and then only if both
607 the kernel and pppd were compiled with PPP_FILTER defined.
610 Do not exit after a connection is terminated; instead try to reopen
614 Request that the peer compress frames that it sends using Predictor-1
615 compression, and agree to compress transmitted frames with Predictor-1
616 if requested. This option has no effect unless the kernel driver
617 supports Predictor-1 compression.
620 Add an entry to this system's ARP [Address Resolution Protocol] table
621 with the IP address of the peer and the Ethernet address of this
622 system. This will have the effect of making the peer appear to other
623 systems to be on the local ethernet.
625 .B remotename \fIname
626 Set the assumed name of the remote system for authentication purposes
630 With this option, pppd will not agree to authenticate itself to the
634 With this option, pppd will not agree to authenticate itself to the
638 Require the peer to authenticate itself using CHAP [Challenge
639 Handshake Authentication Protocol] authentication.
642 Require the peer to authenticate itself using PAP [Password
643 Authentication Protocol] authentication.
646 With this option, pppd will not transmit LCP packets to initiate a
647 connection until a valid LCP packet is received from the peer (as for
648 the `passive' option with ancient versions of pppd).
651 Enforce the use of the hostname (with domain name appended, if given)
652 as the name of the local system for authentication purposes (overrides
653 the \fIname\fR option).
656 Sets the name used for authenticating the local system to the peer to
660 Sets the number of connection slots to be used by the Van Jacobson
661 TCP/IP header compression and decompression code to \fIn\fR, which
662 must be between 2 and 16 (inclusive).
665 Run the executable or shell command specified by \fIscript\fR before
666 initiating PPP negotiation, after the connect script (if any) has
667 completed. This option is privileged if the \fInoauth\fR option is
671 Use software flow control (i.e. XON/XOFF) to control the flow of data on
674 Options can be taken from files as well as the command line. Pppd
675 reads options from the files /etc/ppp/options, ~/.ppprc and
676 /etc/ppp/options.\fIttyname\fR (in that order) before processing the
677 options on the command line. (In fact, the command-line options are
678 scanned to find the terminal name before the options.\fIttyname\fR
679 file is read.) In forming the name of the options.\fIttyname\fR file,
680 the initial /dev/ is removed from the terminal name, and any remaining
681 / characters are replaced with dots.
683 An options file is parsed into a series of words, delimited by
684 whitespace. Whitespace can be included in a word by enclosing the
685 word in double-quotes ("). A backslash (\\) quotes the following character.
686 A hash (#) starts a comment, which continues until the end of the
687 line. There is no restriction on using the \fIfile\fR or \fIcall\fR
688 options within an options file.
691 provides system administrators with sufficient access control that PPP
692 access to a server machine can be provided to legitimate users without
693 fear of compromising the security of the server or the network it's
694 on. In part this is provided by the /etc/ppp/options file, where the
695 administrator can place options to restrict the ways in which pppd can
696 be used, and in part by the PAP and CHAP secrets files, where the
697 administrator can restrict the set of IP addresses which individual
700 The normal way that pppd should be set up is to have the \fIauth\fR
701 option in the /etc/ppp/options file. (This may become the default in
702 later releases.) If users wish to use pppd to dial out to a peer
703 which will refuse to authenticate itself (such as an internet service
704 provider), the system administrator should create an options file
705 under /etc/ppp/peers containing the \fInoauth\fR option, the name of
706 the serial port to use, and the \fIconnect\fR option (if required),
707 plus any other appropriate options. In this way, pppd can be set up
708 to allow non-privileged users to make unauthenticated connections only
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 an 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, or an
774 override for "local:remote" addresses (the same format used on the
775 command line or in the options file) when on a line that contains a
776 specific client name (not a wildcard nor empty).
777 If there are only 3 words
778 on the line, or if the first word is "-", then all IP addresses are
779 disallowed. To allow any address, use "*".
780 A word starting with "!" indicates that the
781 specified address is \fInot\fR acceptable. An address may be followed
782 by "/" and a number \fIn\fR, to indicate a whole subnet, i.e. all
783 addresses which have the same value in the most significant \fIn\fR
784 bits. Note that case is significant in the client and server names
787 If the secret starts with an `@', what follows is assumed to be the
788 name of a file from which to read the secret. A "*" as the client or
789 server name matches any name. When selecting a secret, pppd takes the
790 best match, i.e. the match with the fewest wildcards.
792 Thus a secrets file contains both secrets for use in authenticating
793 other hosts, plus secrets which we use for authenticating ourselves to
794 others. When pppd is authenticating the peer (checking the peer's
795 identity), it chooses a secret with the peer's name in the first
796 field and the name of the local system in the second field. The
797 name of the local system defaults to the hostname, with the domain
798 name appended if the \fIdomain\fR option is used. This default can be
799 overridden with the \fIname\fR option, except when the
800 \fIusehostname\fR option is used.
802 When pppd is choosing a secret to use in authenticating itself to the
803 peer, it first determines what name it is going to use to identify
804 itself to the peer. This name can be specified by the user with the
805 \fIuser\fR option. If this option is not used, the name defaults to
806 the name of the local system, determined as described in the previous
807 paragraph. Then pppd looks for a secret with this name in the first
808 field and the peer's name in the second field. Pppd will know the
809 name of the peer if CHAP authentication is being used, because the
810 peer will have sent it in the challenge packet. However, if PAP is being
811 used, pppd will have to determine the peer's name from the options
812 specified by the user. The user can specify the peer's name directly
813 with the \fIremotename\fR option. Otherwise, if the remote IP address
814 was specified by a name (rather than in numeric form), that name will
815 be used as the peer's name. Failing that, pppd will use the null
816 string as the peer's name.
818 When authenticating the peer with PAP, the supplied password is first
819 compared with the secret from the secrets file. If the password
820 doesn't match the secret, the password is encrypted using crypt() and
821 checked against the secret again. Thus secrets for authenticating the
822 peer can be stored in encrypted form if desired. If the
823 \fIpapcrypt\fR option is given, the first (unencrypted) comparison is
824 omitted, for better security.
826 Furthermore, if the \fIlogin\fR option was specified, the username and
827 password are also checked against the system password database. Thus,
828 the system administrator can set up the pap-secrets file to allow PPP
829 access only to certain users, and to restrict the set of IP addresses
830 that each user can use. Typically, when using the \fIlogin\fR option,
831 the secret in /etc/ppp/pap-secrets would be "", which will match any
832 password supplied by the peer. This avoids the need to have the same
833 secret in two places.
835 Additional checks are performed when the \fBlogin\fR option is used.
836 If the file /etc/ppp/ppp.deny exists, and the user is listed in it,
837 the authentication fails. If the file /etc/ppp/ppp.shells exists and
838 the user's normal login shell is not listed, the authentication fails.
840 Authentication must be satisfactorily completed before IPCP (or any
841 other Network Control Protocol) can be started. If the peer is
842 required to authenticate itself, and fails to do so, pppd will
843 terminated the link (by closing LCP). If IPCP negotiates an
844 unacceptable IP address for the remote host, IPCP will be closed. IP
845 packets can only be sent or received when IPCP is open.
847 In some cases it is desirable to allow some hosts which can't
848 authenticate themselves to connect and use one of a restricted set of
849 IP addresses, even when the local host generally requires
850 authentication. If the peer refuses to authenticate itself when
851 requested, pppd takes that as equivalent to authenticating with PAP
852 using the empty string for the username and password. Thus, by adding
853 a line to the pap-secrets file which specifies the empty string for
854 the client and password, it is possible to allow restricted access to
855 hosts which refuse to authenticate themselves.
858 When IPCP negotiation is completed successfully, pppd will inform the
859 kernel of the local and remote IP addresses for the ppp interface.
860 This is sufficient to create a host route to the remote end of the
861 link, which will enable the peers to exchange IP packets.
862 Communication with other machines generally requires further
863 modification to routing tables and/or ARP (Address Resolution
864 Protocol) tables. In most cases the \fIdefaultroute\fR and/or
865 \fIproxyarp\fR options are sufficient for this, but in some cases
866 further intervention is required. The /etc/ppp/ip-up script can be
869 Sometimes it is desirable to add a default route through the remote
870 host, as in the case of a machine whose only connection to the
871 Internet is through the ppp interface. The \fIdefaultroute\fR option
872 causes pppd to create such a default route when IPCP comes up, and
873 delete it when the link is terminated.
875 In some cases it is desirable to use proxy ARP, for example on a
876 server machine connected to a LAN, in order to allow other hosts to
877 communicate with the remote host. The \fIproxyarp\fR option causes
878 pppd to look for a network interface on the same subnet as the remote
879 host (an interface supporting broadcast and ARP, which is up and not a
880 point-to-point or loopback interface). If found, pppd creates a
881 permanent, published ARP entry with the IP address of the remote host
882 and the hardware address of the network interface found.
884 When the \fIdemand\fR option is used, the interface IP addresses have
885 already been set at the point when IPCP comes up. If pppd has not
886 been able to negotiate the same addresses that it used to configure
887 the interface (for example when the peer is an ISP that uses dynamic
888 IP address assignment), pppd has to change the interface IP addresses
889 to the negotiated addresses. This may disrupt existing connections,
890 and the use of demand dialling with peers that do dynamic IP address
891 assignment is not recommended.
894 The following examples assume that the /etc/ppp/options file contains
895 the \fIauth\fR option (as in the default /etc/ppp/options file in the
898 Probably the most common use of pppd is to dial out to an ISP. This
899 can be done with a command such as
903 where the /etc/ppp/peers/isp file is set up by the system
904 administrator to contain something like this:
908 connect '/usr/sbin/chat -v -f /etc/ppp/chat-isp'
912 In this example, we are using chat to dial the ISP's modem and go
913 through any logon sequence required. The /etc/ppp/chat-isp file
914 contains the script used by chat; it could for example contain
927 ABORT "Username/Password Incorrect"
937 "word:" "\\qmypassword"
943 See the chat(8) man page for details of chat scripts.
945 Pppd can also be used to provide a dial-in ppp service for users. If
946 the users already have login accounts, the simplest way to set up the
947 ppp service is to let the users log in to their accounts and run pppd
948 (installed setuid-root) with a command such as
952 To allow a user to use the PPP facilities, you need to allocate an IP
953 address for that user's machine and create an entry in
954 /etc/ppp/pap-secrets or /etc/ppp/chap-secrets (depending on which
955 authentication method the PPP implementation on the user's machine
956 supports), so that the user's
957 machine can authenticate itself. For example, if Joe has a machine
958 called "joespc" which is to be allowed to dial in to the machine
959 called "server" and use the IP address joespc.my.net, you would add an
960 entry like this to /etc/ppp/pap-secrets or /etc/ppp/chap-secrets:
962 joespc server "joe's secret" joespc.my.net
964 Alternatively, you can create a username called (for example) "ppp",
965 whose login shell is pppd and whose home directory is /etc/ppp.
966 Options to be used when pppd is run this way can be put in
969 If your serial connection is any more complicated than a piece of
970 wire, you may need to arrange for some control characters to be
971 escaped. In particular, it is often useful to escape XON (^Q) and
972 XOFF (^S), using \fIasyncmap a0000\fR. If the path includes a telnet,
973 you probably should escape ^] as well (\fIasyncmap 200a0000\fR). If
974 the path includes an rlogin, you will need to use the \fIescape ff\fR
975 option on the end which is running the rlogin client, since many
976 rlogin implementations are not transparent; they will remove the
977 sequence [0xff, 0xff, 0x73, 0x73, followed by any 8 bytes] from the
981 Messages are sent to the syslog daemon using facility LOG_DAEMON.
982 (This can be overriden by recompiling pppd with the macro
983 LOG_PPP defined as the desired facility.) In order to see the error
984 and debug messages, you will need to edit your /etc/syslog.conf file
985 to direct the messages to the desired output device or file.
987 The \fIdebug\fR option causes the contents of all control packets sent
988 or received to be logged, that is, all LCP, PAP, CHAP or IPCP packets.
989 This can be useful if the PPP negotiation does not succeed or if
990 authentication fails.
991 If debugging is enabled at compile time, the \fIdebug\fR option also
992 causes other debugging messages to be logged.
994 Debugging can also be enabled or disabled by sending a SIGUSR1 signal
995 to the pppd process. This signal acts as a toggle.
997 Pppd invokes scripts at various stages in its processing which can be
998 used to perform site-specific ancillary processing. These scripts are
999 usually shell scripts, but could be executable code files instead.
1000 Pppd does not wait for the scripts to finish. The scripts are
1001 executed as root (with the real and effective user-id set to 0), so
1002 that they can do things such as update routing tables or run
1003 privileged daemons. Be careful that the contents of these scripts do
1004 not compromise your system's security. Pppd runs the scripts with
1005 standard input, output and error redirected to /dev/null, and with an
1006 environment that is empty except for some environment variables that
1007 give information about the link. The environment variables that pppd
1011 The name of the serial tty device being used.
1014 The name of the network interface being used.
1017 The IP address for the local end of the link. This is only set when
1021 The IP address for the remote end of the link. This is only set when
1025 The authenticated name of the peer. This is only set if the peer
1026 authenticates itself.
1029 The baud rate of the tty device.
1032 The real user-id of the user who invoked pppd.
1034 Pppd invokes the following scripts, if they exist. It is not an error
1035 if they don't exist.
1038 A program or script which is executed after the remote system
1039 successfully authenticates itself. It is executed with the parameters
1041 \fIinterface-name peer-name user-name tty-device speed\fR
1043 Note that this script is not executed if the peer doesn't authenticate
1044 itself, for example when the \fInoauth\fR option is used.
1046 .B /etc/ppp/auth-down
1047 A program or script which is executed when the link goes down, if
1048 /etc/ppp/auth-up was previously executed. It is executed in the same
1049 manner with the same parameters as /etc/ppp/auth-up.
1052 A program or script which is executed when the link is available for
1053 sending and receiving IP packets (that is, IPCP has come up). It is
1054 executed with the parameters
1056 \fIinterface-name tty-device speed local-IP-address
1057 remote-IP-address ipparam\fR
1060 A program or script which is executed when the link is no longer
1061 available for sending and receiving IP packets. This script can be
1062 used for undoing the effects of the /etc/ppp/ip-up script. It is
1063 invoked in the same manner and with the same parameters as the ip-up
1067 A program or script which is executed when the link is available for
1068 sending and receiving IPX packets (that is, IPXCP has come up). It is
1069 executed with the parameters
1071 \fIinterface-name tty-device speed network-number local-IPX-node-address
1072 remote-IPX-node-address local-IPX-routing-protocol remote-IPX-routing-protocol
1073 local-IPX-router-name remote-IPX-router-name ipparam pppd-pid\fR
1075 The local-IPX-routing-protocol and remote-IPX-routing-protocol field
1076 may be one of the following:
1078 NONE to indicate that there is no routing protocol
1080 RIP to indicate that RIP/SAP should be used
1082 NLSP to indicate that Novell NLSP should be used
1084 RIP NLSP to indicate that both RIP/SAP and NLSP should be used
1086 .B /etc/ppp/ipx-down
1087 A program or script which is executed when the link is no longer
1088 available for sending and receiving IPX packets. This script can be
1089 used for undoing the effects of the /etc/ppp/ipx-up script. It is
1090 invoked in the same manner and with the same parameters as the ipx-up
1094 .B /var/run/ppp\fIn\fB.pid \fR(BSD or Linux), \fB/etc/ppp/ppp\fIn\fB.pid \fR(others)
1095 Process-ID for pppd process on ppp interface unit \fIn\fR.
1097 .B /etc/ppp/pap-secrets
1098 Usernames, passwords and IP addresses for PAP authentication. This
1099 file should be owned by root and not readable or writable by any other
1100 user. Pppd will log a warning if this is not the case.
1102 .B /etc/ppp/chap-secrets
1103 Names, secrets and IP addresses for CHAP authentication. As for
1104 /etc/ppp/pap-secrets, this file should be owned by root and not
1105 readable or writable by any other user. Pppd will log a warning if
1106 this is not the case.
1109 System default options for pppd, read before user default options or
1110 command-line options.
1113 User default options, read before /etc/ppp/options.\fIttyname\fR.
1115 .B /etc/ppp/options.\fIttyname
1116 System default options for the serial port being used, read after
1117 ~/.ppprc. In forming the \fIttyname\fR part of this
1118 filename, an initial /dev/ is stripped from the port name (if
1119 present), and any slashes in the remaining part are converted to
1123 A directory containing options files which may contain privileged
1124 options, even if pppd was invoked by a user other than root. The
1125 system administrator can create options files in this directory to
1126 permit non-privileged users to dial out without requiring the peer to
1127 authenticate, but only to certain trusted peers.
1129 .B /etc/ppp/ppp.deny
1130 Lists users who may not use the system password PAP authentication.
1132 .B /etc/ppp/ppp.shells
1133 Lists user shells which are approved for system password PAP authentication
1136 .B /usr/share/examples/pppd/
1137 Sample pppd configuration files.
1144 \fICompressing TCP/IP headers for low-speed serial links.\fR
1149 .I The MD5 Message-Digest Algorithm.
1154 .I PPP Internet Protocol Control Protocol (IPCP).
1158 Lloyd, B.; Simpson, W.A.
1159 .I PPP authentication protocols.
1164 .I The Point\-to\-Point Protocol (PPP).
1169 .I PPP in HDLC-like Framing.
1172 The following signals have the specified effect when sent to pppd.
1175 These signals cause pppd to terminate the link (by closing LCP),
1176 restore the serial device settings, and exit.
1179 This signal causes pppd to terminate the link, restore the serial
1180 device settings, and close the serial device. If the \fIpersist\fR or
1181 \fIdemand\fR option has been specified, pppd will try to reopen the
1182 serial device and start another connection (after the holdoff period).
1183 Otherwise pppd will exit. If this signal is received during the
1184 holdoff period, it causes pppd to end the holdoff period immediately.
1187 This signal toggles the state of the \fIdebug\fR option.
1190 This signal causes pppd to renegotiate compression. This can be
1191 useful to re-enable compression after it has been disabled as a result
1192 of a fatal decompression error. (Fatal decompression errors generally
1193 indicate a bug in one or other implementation.)
1196 Paul Mackerras (Paul.Mackerras@cs.anu.edu.au), based on earlier work by
projects / FreeBSD / FreeBSD.git / blob