1 .\" manual page [] for pppd 2.0
2 .\" $Id: pppd.8,v 1.5 1994/05/24 11:27:08 paulus Exp $
4 .\" SS subsection heading
6 .\" IP indented paragraph
10 pppd \- Point to Point Protocol daemon
22 The Point-to-Point Protocol (PPP) provides a method for transmitting
23 datagrams over serial point-to-point links. PPP
24 is composed of three parts: a method for encapsulating datagrams over
25 serial links, an extensible Link Control Protocol (LCP), and
26 a family of Network Control Protocols (NCP) for establishing
27 and configuring different network-layer protocols.
29 The encapsulation scheme is provided by driver code in the kernel.
31 provides the basic LCP, authentication support, and an
32 NCP for establishing and configuring the Internet Protocol (IP)
33 (called the IP Control Protocol, IPCP).
34 .SH FREQUENTLY USED OPTIONS
37 Communicate over the named device. The string "/dev/"
38 is prepended if necessary. If no device name is given,
40 will use the controlling terminal, and will not fork to put itself in
44 Set the baud rate to <speed>. On systems such as 4.4BSD and NetBSD,
45 any speed can be specified. Other systems (e.g. SunOS) allow only a
46 limited set of speeds.
49 Set the async character map to <map>.
50 This map describes which control characters cannot be successfully
51 received over the serial line.
53 will ask the peer to send these characters as a 2-byte escape sequence.
54 The argument is a 32 bit hex number
55 with each bit representing a character to escape.
56 Bit 0 (00000001) represents the character 0x00;
57 bit 31 (80000000) represents the character 0x1f or ^_.
58 If multiple \fBasyncmap\fR options are
59 given, the values are ORed together.
60 If no \fBasyncmap\fR option is given, no async character map will be
61 negotiated for the receive direction; the peer will then escape
62 \fIall\fR control characters.
65 Require the peer to authenticate itself before allowing network
66 packets to be sent or received.
69 Use the executable or shell command specified by \fI<p>\fR to set up the
70 serial line. This script would typically use the "chat" program to
71 dial the modem and start the remote ppp session.
74 Use hardware flow control (i.e. RTS/CTS) to control the flow of data on
78 Use software flow control (i.e. XON/XOFF) to control the flow of data on
79 the serial port. This option is not implemented on BSD or Ultrix systems
83 A synonym for \fBxonxoff\fR.
86 Add a default route to the system routing tables, using the peer as
87 the gateway, when IPCP negotiation is successfully completed.
88 This entry is removed when the PPP connection is broken.
91 Run the executable or shell command specified by \fI<p>\fR after
92 \fIpppd\fR has terminated the link. This script could, for example,
93 issue commands to the modem to cause it to hang up if hardware modem
94 control signals were not available.
96 .B escape \fIxx,yy,...
97 Specifies that certain characters should be escaped on transmission
98 (regardless of whether the peer requests them to be escaped with its
99 async control character map). The characters to be escaped are
100 specified as a list of hex numbers separated by commas. Note that
101 almost any character can be specified for the \fBescape\fR option,
102 unlike the \fBasyncmap\fR option which only allows control characters
103 to be specified. The characters which may not be escaped are those
104 with hex values 0x20 - 0x3f or 0x5e.
107 Read options from file <f> (the format is described below).
110 Specifies that \fIpppd\fR should use a UUCP-style lock on the serial
111 device to ensure exclusive access to the device.
114 Set the MRU [Maximum Receive Unit] value to <n> for negotiation.
116 will ask the peer to send packets of no more than <n> bytes.
117 The minimum MRU value is 128.
118 The default MRU value is 1500. A value of 296 is recommended for slow
119 links (40 bytes for TCP/IP header + 256 bytes of data).
122 Set the interface netmask to <n>, a 32 bit netmask in "decimal dot" notation
123 (e.g. 255.255.255.0).
126 Enables the "passive" option in the LCP. With this option,
128 will attempt to initiate a connection; if no reply is received from
131 will then just wait passively for a valid LCP packet from the peer
132 (instead of exiting, as it does without this option).
137 will not transmit LCP packets to initiate a connection until a valid
138 LCP packet is received from the peer (as for the "passive" option with
139 old versions of \fIpppd\fR).
142 .I <local_IP_address>\fB:\fI<remote_IP_address>
143 Set the local and/or remote interface IP addresses. Either one may be
144 omitted. The IP addresses can be specified with a host name or in
145 decimal dot notation (e.g. 150.234.56.78). The default local
146 address is the (first) IP address of the system (unless the
148 option is given). The remote address will be obtained from the peer
149 if not specified in any option. Thus, in simple cases, this option is
151 If a local and/or remote IP address is specified with this option,
153 will not accept a different value from the peer in the IPCP
154 negotiation, unless the
157 .B ipcp-accept-remote
158 options are given, respectively.
161 Don't request or allow negotiation of any options for LCP and IPCP (use
165 Disable Address/Control compression negotiation (use default, i.e.
166 address/control field disabled).
169 Disable asyncmap negotiation (use the default asyncmap, i.e. escape
170 all control characters).
177 Increase debugging level (same as the \fBdebug\fR option).
180 Don't fork to become a background process (otherwise
182 will do so if a serial device is specified).
185 Disable IP address negotiation (with this option, the remote IP
186 address must be specified with an option on the command line or in an
190 Disable magic number negotiation. With this option,
192 cannot detect a looped-back line.
195 Disable MRU [Maximum Receive Unit] negotiation (use default, i.e. 1500).
203 Disable protocol field compression negotiation (use default, i.e.
204 protocol field compression disabled).
207 Agree to authenticate using PAP [Password Authentication Protocol] if
208 requested by the peer, and
209 use the data in file <p> for the user and password to send to the
210 peer. The file contains the remote user name, followed by a newline,
211 followed by the remote password, followed by a newline. This option
215 Require the peer to authenticate itself using PAP.
218 Don't agree to authenticate using PAP.
221 Require the peer to authenticate itself using CHAP [Cryptographic
222 Handshake Authentication Protocol] authentication.
225 Don't agree to authenticate using CHAP.
228 Disable negotiation of Van Jacobson style IP header compression (use
229 default, i.e. no compression).
232 Increase debugging level (same as \fB\-d\fR).
234 option is given, \fIpppd\fR will log the contents of all control
235 packets sent or received in a readable form. The packets are logged
236 through syslog with facility \fIdaemon\fR and level \fIdebug\fR. This
237 information can be directed to a file by setting up /etc/syslog.conf
238 appropriately (see syslog.conf(5)).
241 Append the domain name <d> to the local host name for authentication
242 purposes. For example, if gethostname() returns the name porsche, but the
243 fully qualified domain name is porsche.Quotron.COM, you would use the
244 domain option to set the domain name to Quotron.COM.
247 Use the modem control lines. On Ultrix, this option implies hardware
248 flow control, as for the \fBcrtscts\fR option. (This option is not fully
252 Enable debugging code in the kernel-level PPP driver. The argument
253 \fIn\fR is a number which is the sum of the following values: 1 to
254 enable general debug messages, 2 to request that the contents of
255 received packets be printed, and 4 to request that the contents of
256 transmitted packets be printed.
259 Don't use the modem control lines.
262 Set the MTU [Maximum Transmit Unit] value to \fI<n>\fR. Unless the
263 peer requests a smaller value via MRU negotiation, \fIpppd\fR will
264 request that the kernel networking code send data packets of no more
265 than \fIn\fR bytes through the PPP network interface.
268 Set the name of the local system for authentication purposes to <n>.
271 Set the user name to use for authenticating this machine with the peer
275 Enforce the use of the hostname as the name of the local system for
276 authentication purposes (overrides the
281 Set the assumed name of the remote system for authentication purposes
285 Add an entry to this system's ARP [Address Resolution Protocol] table
286 with the IP address of the peer and the Ethernet address of this
290 Use the system password database for authenticating the peer using
294 Disables the default behaviour when no local IP address is specified,
295 which is to determine (if possible) the local IP address from the
296 hostname. With this option, the peer will have to supply the local IP
297 address during IPCP negotiation (unless it specified explicitly on the
298 command line or in an options file).
300 .B lcp-echo-interval \fI<n>
301 If this option is given, \fIpppd\fR will send an LCP echo-request
302 frame to the peer every \fIn\fR seconds. Under Linux, the
303 echo-request is sent when no packets have been received from the peer
304 for \fIn\fR seconds. Normally the peer should respond to the
305 echo-request by sending an echo-reply. This option can be used with
306 the \fIlcp-echo-failure\fR option to detect that the peer is no longer
309 .B lcp-echo-failure \fI<n>
310 If this option is given, \fIpppd\fR will presume the peer to be dead
311 if \fIn\fR LCP echo-requests are sent without receiving a valid LCP
312 echo-reply. If this happens, \fIpppd\fR will terminate the
313 connection. Use of this option requires a non-zero value for the
314 \fIlcp-echo-interval\fR parameter. This option can be used to enable
315 \fIpppd\fR to terminate after the physical connection has been broken
316 (e.g., the modem has hung up) in situations where no hardware modem
317 control lines are available.
319 .B lcp-restart \fI<n>
320 Set the LCP restart interval (retransmission timeout) to <n> seconds
323 .B lcp-max-terminate \fI<n>
324 Set the maximum number of LCP terminate-request transmissions to <n>
327 .B lcp-max-configure \fI<n>
328 Set the maximum number of LCP configure-request transmissions to <n>
331 .B lcp-max-failure \fI<n>
332 Set the maximum number of LCP configure-NAKs returned before starting
333 to send configure-Rejects instead to <n> (default 10).
335 .B ipcp-restart \fI<n>
336 Set the IPCP restart interval (retransmission timeout) to <n> seconds
339 .B ipcp-max-terminate \fI<n>
340 Set the maximum number of IPCP terminate-request transmissions to <n>
343 .B ipcp-max-configure \fI<n>
344 Set the maximum number of IPCP configure-request transmissions to <n>
347 .B ipcp-max-failure \fI<n>
348 Set the maximum number of IPCP configure-NAKs returned before starting
349 to send configure-Rejects instead to <n> (default 10).
351 .B pap-restart \fI<n>
352 Set the PAP restart interval (retransmission timeout) to <n> seconds
355 .B pap-max-authreq \fI<n>
356 Set the maximum number of PAP authenticate-request transmissions to
359 .B chap-restart \fI<n>
360 Set the CHAP restart interval (retransmission timeout for challenges)
361 to <n> seconds (default 3).
363 .B chap-max-challenge \fI<n>
364 Set the maximum number of CHAP challenge transmissions to <n> (default
367 .B chap-interval \fI<n>
368 If this option is given,
370 will rechallenge the peer every <n> seconds.
375 will accept the peer's idea of our local IP address, even if the
376 local IP address was specified in an option.
378 .B ipcp-accept-remote
381 will accept the peer's idea of its (remote) IP address, even if the
382 remote IP address was specified in an option.
384 Options can be taken from files as well as the command line.
386 reads options from the files /etc/ppp/options and ~/.ppprc before
387 looking at the command line. An options file is parsed into a series
388 of words, delimited by whitespace. Whitespace can be included in a
389 word by enclosing the word in quotes ("). A backslash (\\) quotes the
390 following character. A hash (#) starts a comment, which continues
391 until the end of the line.
394 provides system administrators with sufficient access control that PPP
395 access to a server machine can be provided to legitimate users without
396 fear of compromising the security of the server or the network it's
397 on. In part this is provided by the /etc/ppp/options file, where the
398 administrator can place options to require authentication whenever
400 is run, and in part by the PAP and CHAP secrets files, where the
401 administrator can restrict the set of IP addresses which individual
404 The default behaviour of
406 is to agree to authenticate if requested, and to not
407 require authentication from the peer. However,
410 authenticate itself with a particular protocol if it has no secrets
411 which could be used to do so.
413 Authentication is based on secrets, which are selected from secrets
414 files (/etc/ppp/pap-secrets for PAP, /etc/ppp/chap-secrets for CHAP).
415 Both secrets files have the same format, and both can store secrets
416 for several combinations of server (authenticating peer) and client
417 (peer being authenticated). Note that
420 and client, and that different protocols can be used in the two
421 directions if desired.
423 A secrets file is parsed into words as for a options file. A secret
424 is specified by a line containing at least 3 words, in the order
425 client, server, secret. Any following words on the same line are
426 taken to be a list of acceptable IP addresses for that client. If
427 there are only 3 words on the line, it is assumed that any IP address
428 is OK; to disallow all IP addresses, use "-". If the secret starts
429 with an `@', what follows is assumed to be the name of a file from
430 which to read the secret. A "*" as the client or server name matches
431 any name. When selecting a secret, \fIpppd\fR takes the best match, i.e.
432 the match with the fewest wildcards.
434 Thus a secrets file contains both secrets for use in authenticating
435 other hosts, plus secrets which we use for authenticating ourselves to
436 others. Which secret to use is chosen based on the names of the host
437 (the `local name') and its peer (the `remote name'). The local name
440 if the \fBusehostname\fR option is given,
441 then the local name is the hostname of this machine
442 (with the domain appended, if given)
444 else if the \fBname\fR option is given,
445 then use the argument of the first \fBname\fR option seen
447 else if the local IP address is specified with a hostname,
450 else use the hostname of this machine (with the domain appended, if given)
452 When authenticating ourselves using PAP, there is also a `username'
453 which is the local name by default, but can be set with the \fBuser\fR
454 option or the \fB+ua\fR option.
456 The remote name is set as follows:
458 if the \fBremotename\fR option is given,
459 then use the argument of the last \fBremotename\fR option seen
461 else if the remote IP address is specified with a hostname,
462 then use that host name
464 else the remote name is the null string "".
466 Secrets are selected from the PAP secrets file as follows:
469 For authenticating the peer, look for a secret with client ==
470 username specified in the PAP authenticate-request, and server ==
474 For authenticating ourselves to the peer, look for a secret with
475 client == our username, server == remote name.
477 When authenticating the peer with PAP, a secret of "" matches any
478 password supplied by the peer. If the password doesn't match the
479 secret, the password is encrypted using crypt() and checked against
480 the secret again; thus secrets for authenticating the peer can be
481 stored in encrypted form. If the \fBlogin\fR option was specified, the
482 username and password are also checked against the system password
483 database. Thus, the system administrator can set up the pap-secrets
484 file to allow PPP access only to certain users, and to restrict the
485 set of IP addresses that each user can use.
487 Secrets are selected from the CHAP secrets file as follows:
490 For authenticating the peer, look for a secret with client == name
491 specified in the CHAP-Response message, and server == local name.
494 For authenticating ourselves to the peer, look for a secret with
495 client == local name, and server == name specified in the
496 CHAP-Challenge message.
498 Authentication must be satisfactorily completed before IPCP (or any
499 other Network Control Protocol) can be started. If authentication
500 fails, \fIpppd\fR will terminated the link (by closing LCP). If IPCP
501 negotiates an unacceptable IP address for the remote host, IPCP will
502 be closed. IP packets can only be sent or received when IPCP is open.
504 In some cases it is desirable to allow some hosts which can't
505 authenticate themselves to connect and use one of a restricted set of
506 IP addresses, even when the local host generally requires
507 authentication. If the peer refuses to authenticate itself when
508 requested, \fIpppd\fR takes that as equivalent to authenticating with
509 PAP using the empty string for the username and password. Thus, by
510 adding a line to the pap-secrets file which specifies the empty string
511 for the client and password, it is possible to allow restricted access
512 to hosts which refuse to authenticate themselves.
515 When IPCP negotiation is completed successfully,
517 will inform the kernel of the local and remote IP addresses for the
518 ppp interface. This is sufficient to create a
519 host route to the remote end of the link, which will enable the peers
520 to exchange IP packets. Communication with other machines generally
521 requires further modification to routing tables and/or ARP (Address
522 Resolution Protocol) tables. In some cases this will be done
523 automatically through the actions of the \fIrouted\fR or \fIgated\fR
524 daemons, but in most cases some further intervention is required.
526 Sometimes it is desirable
527 to add a default route through the remote host, as in the case of a
528 machine whose only connection to the Internet is through the ppp
529 interface. The \fBdefaultroute\fR option causes \fIpppd\fR to create such a
530 default route when IPCP comes up, and delete it when the link is
533 In some cases it is desirable to use proxy ARP, for example on a
534 server machine connected to a LAN, in order to allow other hosts to
535 communicate with the remote host. The \fBproxyarp\fR option causes \fIpppd\fR
536 to look for a network interface on the same subnet as the remote host
537 (an interface supporting broadcast and ARP, which is up and not a
538 point-to-point or loopback interface). If found, \fIpppd\fR creates a
539 permanent, published ARP entry with the IP address of the remote host
540 and the hardware address of the network interface found.
543 In the simplest case, you can connect the serial ports of two machines
544 and issue a command like
546 pppd /dev/ttya 9600 passive
548 to each machine, assuming there is no \fIgetty\fR running on the
549 serial ports. If one machine has a \fIgetty\fR running, you can use
550 \fIkermit\fR or \fItip\fR on the other machine to log in to the first
551 machine and issue a command like
555 Then exit from the communications program (making sure the connection
556 isn't dropped), and issue a command like
560 The process of logging in to the other machine and starting \fIpppd\fR
561 can be automated by using the \fBconnect\fR option to run \fIchat\fR,
564 pppd /dev/ttya 38400 connect 'chat "" "" "login:" "username"
565 "Password:" "password" "% " "exec pppd passive"'
567 (Note however that running chat like this will leave the password
568 visible in the parameter list of pppd and chat.)
570 If your serial connection is any more complicated than a piece of
571 wire, you may need to arrange for some control characters to be
572 escaped. In particular, it is often useful to escape XON (^Q) and
573 XOFF (^S), using \fBasyncmap a0000\fR. If the path includes a telnet,
574 you probably should escape ^] as well (\fBasyncmap 200a0000\fR).
575 If the path includes an rlogin, you will need to use the \fBescape
576 ff\fR option on the end which is running the rlogin client, since many
577 rlogin implementations are not
578 transparent; they will remove the sequence [0xff, 0xff, 0x73, 0x73,
579 followed by any 8 bytes] from the stream.
582 Messages are sent to the syslog daemon using facility LOG_DAEMON.
583 (This can be overriden by recompiling \fIpppd\fR with the macro
584 LOG_PPP defined as the desired facility.) In order to see the error
585 and debug messages, you will need to edit your /etc/syslog.conf file
586 to direct the messages to the desired output device or file.
588 The \fBdebug\fR option causes the contents of all control packets sent
589 or received to be logged, that is, all LCP, PAP, CHAP or IPCP packets.
590 This can be useful if the PPP negotiation does not succeed.
591 If debugging is enabled at compile time, the \fBdebug\fR option also
592 causes other debugging messages to be logged.
594 Debugging can also be enabled by sending a
598 Debugging may be disabled by sending a SIGUSR2 to the
603 .B /var/run/ppp\fIn\fB.pid \fR(BSD), \fB/etc/ppp/ppp\fIn\fB.pid \fR(SunOS)
604 Process-ID for \fIpppd\fR process on ppp interface unit \fIn\fR.
607 A program or script which is executed when the link is available for
608 sending and receiving IP packets (that is, IPCP has come up). It is
609 executed with the parameters \fIinterface-name tty-device speed
610 local-IP-address remote-IP-address\fR.
612 This program or script is executed with the same real and effective
613 user-ID as \fIpppd\fR, that is, at least the effective user-ID and
614 possibly the real user-ID will be \fBroot\fR. This is so that it can
615 be used to manipulate routes, run privileged daemons (e.g.
616 \fBsendmail\fR), etc. Be careful that the contents of the
617 /etc/ppp/ip-up and /etc/ppp/ip-down scripts do not compromise your
621 A program or script which is executed when the link is no longer
622 available for sending and receiving IP packets. This script can be
623 used for undoing the effects of the /etc/ppp/ip-up script. It is
624 invoked with the same parameters as the ip-up script, and the same
625 security considerations apply, since it is executed with the same
626 effective and real user-IDs as \fIpppd\fR.
628 .B /etc/ppp/pap-secrets
629 Usernames, passwords and IP addresses for PAP authentication.
631 .B /etc/ppp/chap-secrets
632 Names, secrets and IP addresses for CHAP authentication.
635 System default options for
637 read before user default options or command-line options.
640 User default options, read before command-line options.
645 .I Compressing TCP/IP headers for low-speed serial links.
650 .I The MD5 Message-Digest Algorithm.
655 .I PPP Internet Protocol Control Protocol (IPCP).
659 Lloyd, B.; Simpson, W.A.
660 .I PPP authentication protocols.
665 .I The Point\-to\-Point Protocol (PPP).
670 .I PPP in HDLC Framing.
673 The following signals have the specified effect when sent to the
678 These signals cause \fIpppd\fR to terminate the link (by closing LCP),
679 restore the serial device settings, and exit.
682 Indicates that the physical layer has been disconnected. \fIpppd\fR
683 will attempt to restore the serial device settings (this may produce
684 error messages on Suns), and then exit.
686 The use of the modem control lines and the effects of the \fBmodem\fR
687 and \fBlocal\fR options are not well defined.
693 Brad Parker (brad@fcr.com),
694 Paul Mackerras (paulus@cs.anu.edu.au)
projects / ppp.git / blob