.\" manual page [] for pppd 2.0 .\" $Id: pppd.8,v 1.4 1993/11/28 23:35:34 paulus Exp $ .\" SH section heading .\" SS subsection heading .\" LP paragraph .\" IP indented paragraph .\" TP hanging label .TH PPPD 8 .SH NAME pppd \- Point to Point Protocol daemon .SH SYNOPSIS .B pppd [ .I options ] [ .I tty_name ] [ .I speed ] .SH DESCRIPTION .LP The Point-to-Point Protocol (PPP) provides a method for transmitting datagrams over serial point-to-point links. PPP is composed of three parts: a method for encapsulating datagrams over serial links, an extensible Link Control Protocol (LCP), and a family of Network Control Protocols (NCP) for establishing and configuring different network-layer protocols. .LP The encapsulation scheme is provided by driver code in the kernel. .B pppd provides the basic LCP, authentication support, and an NCP for establishing and configuring the Internet Protocol (IP) (called the IP Control Protocol, IPCP). .SH FREQUENTLY USED OPTIONS .TP .I Communicate over the named device. The string "/dev/" is prepended if necessary. If no device name is given, .I pppd will use the controlling terminal, and will not fork to put itself in the background. .TP .I Set the baud rate to . On systems such as 4.4BSD and NetBSD, any speed can be specified. Other systems (e.g. SunOS) allow only a limited set of speeds. .TP .B asyncmap \fI Set the async character map to . This map describes which control characters cannot be successfully received over the serial line. .I pppd will ask the peer to send these characters as a 2-byte "escape" sequence. The argument is a 32 bit hex number with each bit representing a character to escape. Bit 0 (00000001) represents the character 0x00; bit 31 (80000000) represents the character 0x1f or ^_. The default asyncmap is 0. If multiple \fBasyncmap\fR options are given, the values are ORed together. .TP .B auth Require the peer to authenticate itself before allowing network packets to be sent or received. .TP .B connect \fI

Use the executable or shell command specified by

to set up the serial line. This script would typically use the "chat" program to dial the modem and start the remote ppp session. .TP .B crtscts Use hardware flow control (i.e. RTS/CTS) to control the flow of data on the serial port. .TP .B defaultroute Add a default route to the system routing tables, using the peer as the gateway, when IPCP negotiation is successfully completed. This entry is removed when the PPP connection is broken. .TP .B file \fI Read options from file (the format is described below). .TP .B mru \fI Set the MRU [Maximum Receive Unit] value to for negotiation. .I pppd will ask the peer to send packets of no more than bytes. The minimum MRU value is 128. The default MRU value is 1500. A value of 296 is recommended for slow links (40 bytes for TCP/IP header + 256 bytes of data). .TP .B netmask \fI Set the interface netmask to , a 32 bit netmask in "decimal dot" notation (e.g. 255.255.255.0). .TP .B passive Enables the "passive" option in the LCP. With this option, .I pppd will attempt to initiate a connection; if no reply is received from the peer, .I pppd will then just wait passively for a valid LCP packet from the peer (instead of exiting, as it does without this option). .TP .B silent With this option, .I pppd will not transmit LCP packets to initiate a connection until a valid LCP packet is received from the peer (as for the "passive" option with old versions of \fIpppd\fR). .SH OPTIONS .TP .I \fB:\fI Set the local and/or remote interface IP addresses. Either one may be omitted. The IP addresses can be specified with a host name or in "decimal dot" notation (e.g. "150.203.23.247"). The default local address is the (first) IP address of the system. The remote address will be obtained from the peer if not specified in any option. Thus, in simple cases, this option is not required. .TP .B -all Don't request or allow negotiation of any options for LCP and IPCP (use default values). .TP .B -ac Disable Address/Control compression negotiation (use default, i.e. disabled). .TP .B -am Disable asyncmap negotiation (use default, i.e. 0xffffffff). .TP .B -as \fI Same as .B asyncmap \fI .TP .B -d Increase debugging level. .TP .B -detach Don't fork to become a background process (otherwise .I pppd will do so if a serial device is specified). .TP .B -ip Disable IP address negotiation (with this option, the remote IP address must be specified with an option on the command line or in an options file). .TP .B -mn Disable magic number negotiation. With this option, .I pppd cannot detect a looped-back line. .TP .B -mru Disable MRU [Maximum Receive Unit] negotiation (use default, i.e. 1500). .TP .B -p Same as the .B passive option. .TP .B -pc Disable protocol field compression negotiation (use default, i.e. disabled). .TP .B +ua \fI

Agree to authenticate using PAP [Password Authentication Protocol] if requested by the peer, and use the data in file

for the user and password to send to the peer. The file contains the remote user name, followed by a newline, followed by the remote password, followed by a newline. This option is obsolescent. .TP .B +pap Require the peer to authenticate itself using PAP. .TP .B -pap Don't agree to authenticate using PAP. .TP .B +chap Require the peer to authenticate itself using CHAP [Cryptographic Handshake Authentication Protocol] authentication. .TP .B -chap Don't agree to authenticate using CHAP. .TP .B -vj Disable negotiation of Van Jacobson style IP header compression (use default, i.e. no compression). .TP .B debug Increase debugging level (same as .B -d ). .TP .B domain \fI Append the domain name to the local host name for authentication purposes. For example, if gethostname() returns the name porsche, but the fully qualified domain name is porsche.Quotron.COM, you would use the domain option to set the domain name to Quotron.COM. .TP .B modem Use the modem control lines. (This option is not fully implemented.) .TP .B local Don't use the modem control lines. .TP .B name \fI Set the name of the local system for authentication purposes to . .TP .B user \fI Set the user name to use for authenticating this machine with the peer using PAP to . .TP .B usehostname Enforce the use of the hostname as the name of the local system for authentication purposes (overrides the .B name option). .TP .B remotename \fI Set the assumed name of the remote system for authentication purposes to . .TP .B proxyarp Add an entry to this system's ARP [Address Resolution Protocol] table with the IP address of the peer and the Ethernet address of this system. .TP .B login Use the system password database for authenticating the peer using PAP. .TP .B lcp-restart \fI Set the LCP restart interval (retransmission timeout) to seconds (default 3). .TP .B lcp-max-terminate \fI Set the maximum number of LCP terminate-request transmissions to (default 3). .TP .B lcp-max-configure \fI Set the maximum number of LCP configure-request transmissions to (default 10). .TP .B lcp-max-failure \fI Set the maximum number of LCP configure-NAKs returned before starting to send configure-Rejects instead to (default 10). .TP .B ipcp-restart \fI Set the IPCP restart interval (retransmission timeout) to seconds (default 3). .TP .B ipcp-max-terminate \fI Set the maximum number of IPCP terminate-request transmissions to (default 3). .TP .B ipcp-max-configure \fI Set the maximum number of IPCP configure-request transmissions to (default 10). .TP .B ipcp-max-failure \fI Set the maximum number of IPCP configure-NAKs returned before starting to send configure-Rejects instead to (default 10). .TP .B pap-restart \fI Set the PAP restart interval (retransmission timeout) to seconds (default 3). .TP .B pap-max-authreq \fI Set the maximum number of PAP authenticate-request transmissions to (default 10). .TP .B chap-restart \fI Set the CHAP restart interval (retransmission timeout for challenges) to seconds (default 3). .TP .B chap-max-challenge \fI Set the maximum number of CHAP challenge transmissions to (default 10). .TP .B chap-interval \fI If this option is given, .I pppd will rechallenge the peer every seconds. .SH OPTIONS FILES Options can be taken from files as well as the command line. .I pppd reads options from the files /etc/ppp/options and $HOME/.ppprc before looking at the command line. An options file is parsed into a series of words, delimited by whitespace. Whitespace can be included in a word by enclosing the word in quotes ("). A backslash (\\) quotes the following character. A hash (#) starts a comment, which continues until the end of the line. .SH AUTHENTICATION .I pppd provides system administrators with sufficient access control that PPP access to a server machine can be provided to legitimate users without fear of compromising the security of the server or the network it's on. In part this is provided by the /etc/ppp/options file, where the administrator can place options to require authentication whenever .I pppd is run, and in part by the PAP and CHAP secrets files, where the administrator can restrict the set of IP addresses which individual users may use. .LP The default behaviour of .I pppd is to agree to authenticate if requested, and to not require authentication from the peer. However, .I pppd will not agree to authenticate itself with a particular protocol if it has no secrets which could be used to do so. .LP Authentication is based on secrets, which are selected from secrets files (/etc/ppp/pap-secrets for PAP, /etc/ppp/chap-secrets for CHAP). Both secrets files have the same format, and both can store secrets for several combinations of server (authenticating peer) and client (peer being authenticated). Note that .I pppd can be both a server and client, and that different protocols can be used in the two directions if desired. .LP A secrets file is parsed into words as for a options file. A secret is specified by a line containing at least 3 words, in the order client, server, secret. Any following words on the same line are taken to be a list of acceptable IP addresses for that client. If there are only 3 words on the line, it is assumed that any IP address is OK; to disallow all IP addresses, use "-". If the secret starts with an `@', what follows is assumed to be the name of a file from which to read the secret. A "*" as the client or server name matches any name. When selecting a secret, \fIpppd\fR takes the best match, i.e. the match with the fewest wildcards. .LP Thus a secrets file contains both secrets for use in authenticating other hosts, plus secrets which we use for authenticating ourselves to others. Which secret to use is chosen based on the names of the host (the `local name') and its peer (the `remote name'). The local name is set as follows: .TP 3 if the \fBusehostname\fR option is given, then the local name is the hostname of this machine (with the domain appended, if given) .TP 3 else if the \fBname\fR option is given, then use the argument of the first \fBname\fR option seen .TP 3 else if the local IP address is specified with a hostname, then use that name .TP 3 else use the hostname of this machine (with the domain appended, if given) .LP When authenticating ourselves using PAP, there is also a `username' which is the local name by default, but can be set with the \fBuser\fR option or the \fB+ua\fR option. .LP The remote name is set as follows: .TP 3 if the \fBremotename\fR option is given, then use the argument of the last \fBremotename\fR option seen .TP 3 else if the remote IP address is specified with a hostname, then use that host name .TP 3 else the remote name is the null string "". .LP Secrets are selected from the PAP secrets file as follows: .TP 2 * For authenticating the peer, look for a secret with client == username specified in the PAP authenticate-request, and server == local name. .TP 2 * For authenticating ourselves to the peer, look for a secret with client == our username, server == remote name. .LP When authenticating the peer with PAP, a secret of "" matches any password supplied by the peer. If the password doesn't match the secret, the password is encrypted using crypt() and checked against the secret again; thus secrets for authenticating the peer can be stored in encrypted form. If the \fBlogin\fR option was specified, the username and password are also checked against the system password database. Thus, the system administrator can set up the pap-secrets file to allow PPP access only to certain users, and to restrict the set of IP addresses that each user can use. .LP Secrets are selected from the CHAP secrets file as follows: .TP 2 * For authenticating the peer, look for a secret with client == name specified in the CHAP-Response message, and server == local name. .TP 2 * For authenticating ourselves to the peer, look for a secret with client == local name, and server == name specified in the CHAP-Challenge message. .LP Authentication must be satisfactorily completed before IPCP (or any other Network Control Protocol) can be started. If authentication fails, \fIpppd\fR will terminated the link (by closing LCP). If IPCP negotiates an unacceptable IP address for the remote host, IPCP will be closed. IP packets can only be sent or received when IPCP is open. .SH ROUTING .LP When IPCP negotiation is completed successfully, .I pppd will inform the kernel of the local and remote IP addresses for the ppp interface. This is sufficient to create a host route to the remote end of the link, which will enable the peers to exchange IP packets. Communication with other machines generally requires further modification to routing tables and/or ARP (Address Resolution Protocol) tables. In some cases this will be done automatically through the actions of the \fIrouted\fR or \fIgated\fR daemons, but in most cases some further intervention is required. .LP Sometimes it is desirable to add a default route through the remote host, as in the case of a machine whose only connection to the Internet is through the ppp interface. The \fBdefaultroute\fR option causes \fIpppd\fR to create such a default route when IPCP comes up, and delete it when the link is terminated. .LP In some cases it is desirable to use proxy ARP, for example on a server machine connected to a LAN, in order to allow other hosts to communicate with the remote host. The \fBproxyarp\fR option causes \fIpppd\fR to look for a network interface on the same subnet as the remote host (an interface supporting broadcast and ARP, which is up and not a point-to-point or loopback interface). If found, \fIpppd\fR creates a permanent, published ARP entry with the IP address of the remote host and the hardware address of the network interface found. .SH EXAMPLES .LP In the simplest case, you can connect the serial ports of two machines and issue a command like .IP pppd /dev/ttya 9600 passive .LP to each machine, assuming there is no \fIgetty\fR running on the serial ports. If one machine has a \fIgetty\fR running, you can use \fIkermit\fR or \fItip\fR on the other machine to log in to the first machine and issue a command like .IP pppd passive .LP Then exit from the communications program (making sure the connection isn't dropped), and issue a command like .IP pppd /dev/ttya 9600 .LP The process of logging in to the other machine and starting \fIpppd\fR can be automated by using the \fBconnect\fR option to run \fIchat\fR, for example: .IP pppd /dev/ttya 38400 connect 'chat "" "" "login:" "username" "Password:" "password" "% " "exec pppd passive"' .LP If your serial connection is any more complicated than a piece of wire, you may need to arrange for some control characters to be escaped. In particular, it is often useful to escape XON (^Q) and XOFF (^S), using \fBasyncmap a0000\fR. If the path includes a telnet, you probably should escape ^] as well (\fBasyncmap 200a0000\fR). Don't use an rlogin in the path - many implementations are not transparent; they will remove the sequence [0xff, 0xff, 0x73, 0x73, followed by any 8 bytes] from the stream. .SH DIAGNOSTICS .LP Messages are sent to the syslog daemon using facility LOG_DAEMON unless .I pppd has been compiled with debugging code. In this case the logging facility used will be LOG_LOCAL2 in order to allow separation of the debug output from the other daemons using the LOG_DAEMON facility. You can override this by defining the macro LOG_PPP to the desired facility and recompiling. In order to see the error and debug messages, you will need to edit your /etc/syslog.conf file to direct the messages to the desired output device or file. .LP If enabled at compile time, debugging printout can be enabled by setting the -d or debug flag on the command line, or by sending a SIGUSR1 to the .I pppd process. Debugging may be disabled by sending a SIGUSR2 to the .I pppd process. .SH FILES .TP .B /var/run/ppp\fIn\fB.pid \fR(BSD), \fB/etc/ppp/ppp\fIn\fB.pid \fR(SunOS) Process-ID for \fIpppd\fR process on ppp interface unit \fIn\fR. .TP .B /etc/ppp/pap-secrets Usernames, passwords and IP addresses for PAP authentication. .TP .B /etc/ppp/chap-secrets Names, secrets and IP addresses for CHAP authentication. .TP .B /etc/ppp/options System default options for .I pppd, read before user default options or command-line options. .TP .B $HOME/.ppprc User default options, read before command-line options. .SH SEE ALSO .TP .B RFC1144 Jacobson, V. .I Compressing TCP/IP headers for low-speed serial links. 1990 February. .TP .B RFC1321 Rivest, R. .I The MD5 Message-Digest Algorithm. 1992 April. .TP .B RFC1331 Simpson, W.A. .I Point\-to\-Point Protocol (PPP) for the transmission of multi\-protocol .I datagrams over point\-to\-point links. 1992 May. .TP .B RFC1332 McGregor, G. .I PPP Internet Protocol Control Protocol (IPCP). 1992 May. .TP .B RFC1334 Lloyd, B.; Simpson, W.A. .I PPP authentication protocols. 1992 October. .SH NOTES The following signals have the specified effect when sent to the .I pppd process. .TP .B SIGINT, SIGTERM These signals cause \fIpppd\fR to terminate the link (by closing LCP), restore the serial device settings, and exit. .TP .B SIGHUP Indicates that the physical layer has been disconnected. \fIpppd\fR will attempt to restore the serial device settings (this may produce error messages on Suns), and then exit. .SH BUGS The use of the modem control lines and the effects of the \fBmodem\fR and \fBlocal\fR options are not well defined. .SH AUTHORS Drew Perkins, Brad Clements, Karl Fox, Greg Christy, Brad Parker (brad@fcr.com), Paul Mackerras (paulus@cs.anu.edu.au)