pppd



PPPD(8)                     System Manager's Manual                    PPPD(8)


NAME

     pppd - Point-to-Point Protocol daemon


SYNOPSIS

     pppd [tty_name] [speed] [options]


DESCRIPTION

     PPP is the protocol used for establishing internet links over dial-up
     modems, DSL connections, and many other types of point-to-point links.
     The pppd daemon works together with the kernel ppp(4) driver to establish
     and maintain a PPP link with another system (called the peer) and to
     negotiate Internet Protocol (IP) addresses for each end of the link.
     pppd can also authenticate the peer and/or supply authentication
     information to the peer.  PPP can be used with other network protocols
     besides IP, but such use is becoming increasingly rare.


FREQUENTLY USED OPTIONS

     tty_name
             Use the serial port called ttyname to communicate with the peer.
             The string "/dev/" is prepended to ttyname to form the name of
             the device to open.  If no device name is given, or if the name
             of the terminal connected to the standard input is given, pppd
             will use that terminal, and will not fork to put itself in the
             background.  This option is privileged if the noauth option is
             used.

     speed   An option that is a decimal number is taken as the desired baud
             rate for the serial device.  On systems such as 4.4BSD and
             OpenBSD, any speed can be specified.  Other systems (e.g., Linux,
             SunOS) only support the commonly used baud-rates.

     active-filter filter-expression
             Specifies a packet filter to be applied to data packets to
             determine which packets are to be regarded as link activity, and
             therefore reset the idle timer, or cause the link to be brought
             up in demand-dialling mode.  This option is useful in conjunction
             with the idle option if there are packets being sent or received
             regularly over the link (for example, routing information
             packets) which would otherwise prevent the link from ever
             appearing to be idle.  The filter-expression syntax is as
             described for tcpdump(8), except that qualifiers which are
             inappropriate for a PPP link, such as ether and arp, are not
             permitted.  Generally the filter expression should be enclosed in
             single quotes to prevent whitespace in the expression from being
             interpreted by the shell.

     asyncmap map
             This option sets the Async-Control-Character-Map (ACCM) for this
             end of the link.  The ACCM is a set of 32 bits, one for each of
             the ASCII control characters with values from 0 to 31, where a 1
             bit indicates that the corresponding control character should not
             be used in PPP packets sent to this system.  The map is encoded
             as a hexadecimal number (without a leading 0x) where the least
             significant bit (00000001) represents character 0 and the most
             significant bit (80000000) represents character 31.  pppd will
             ask the peer to send these characters as a 2-byte escape
             sequence.  If multiple asyncmap options are given, the values are
             ORed together.  If no asyncmap option is given, no async
             character map will be negotiated for the receive direction; the
             peer should then escape all control characters.  To escape
             transmitted characters, use the escape option.

     auth    Require the peer to authenticate itself before allowing network
             packets to be sent or received.

     call name
             Read options from the file /etc/ppp/peers/name.  This file may
             contain privileged options, such as noauth, even if pppd is not
             being run by root.  The name string may not begin with "/" or
             include ".." as a pathname component.  The format of the options
             file is described below.

     connect script
             Usually there is something which needs to be done to prepare the
             link before the PPP protocol can be started; for instance, with a
             dial-up modem, commands need to be sent to the modem to dial the
             appropriate phone number.  This option specifies an command for
             pppd to execute (by passing it to a shell) before attempting to
             start PPP negotiation.  The chat(8) program is often useful here,
             as it provides a way to send arbitrary strings to a modem and
             respond to received characters.  This option is privileged if the
             noauth option is used.

     crtscts
             Specifies that pppd should set the serial port to use hardware
             flow control using the RTS and CTS signals in the RS-232
             interface.  If neither the crtscts nor the nocrtscts option is
             given, the hardware flow control setting for the serial port is
             left unchanged.

     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.  This
             option is privileged if the nodefaultroute option has been
             specified.

     disconnect script
             Execute the command specified by script, by passing it to a
             shell, after pppd has terminated the link.  This command could,
             for example, issue commands to the modem to cause it to hang up
             if hardware modem control signals were not available.  The
             disconnect script is not run if the modem has already hung up.
             This option is privileged if the noauth option is used.

     escape xx,yy,...
             Specifies that certain characters should be escaped on
             transmission (regardless of whether the peer requests them to be
             escaped with its async control character map).  The characters to
             be escaped are specified as a list of hex numbers separated by
             commas.  Note that almost any character can be specified for the
             escape option, unlike the asyncmap option which only allows
             control characters to be specified.  The characters which may not
             be escaped are those with hex values 0x20 - 0x3f or 0x5e.

     file name
             Read options from file name (the format is described below).  The
             file must be readable by the user who has invoked pppd.

     lock    Specifies that pppd should create a UUCP-style lock file for the
             serial device to ensure exclusive access to the device.

     mru n   Set the MRU (Maximum Receive Unit) value to n.  pppd will ask the
             peer to send packets of no more than n bytes.  The value of n
             must be between 128 and 16384; the default is 1500.  A value of
             296 works well on very slow links (40 bytes for TCP/IP header +
             256 bytes of data).  Note that for the IPv6 protocol, the MRU
             must be at least 1280.

     mtu n   Set the MTU (Maximum Transmit Unit) value to n.  Unless the peer
             requests a smaller value via MRU negotiation, pppd will request
             that the kernel networking code send data packets of no more than
             n bytes through the PPP network interface.  Note that for the
             IPv6 protocol, the MTU must be at least 1280.

     passive
             Enables the "passive" option in the LCP.  With this option, pppd
             will attempt to initiate a connection; if no reply is received
             from the peer, pppd will then just wait passively for a valid LCP
             packet from the peer, instead of exiting, as it would without
             this option.


OPTIONS

     [local_IP_address]:[remote_IP_address]
             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., 150.234.56.78).  The
             default local address is the (first) IP address of the system
             (unless the noipdefault option is given).  The remote address
             will be obtained from the peer if not specified in any option.
             Thus, in simple cases, this option is not required.  If a local
             and/or remote IP address is specified with this option, pppd will
             not accept a different value from the peer in the IPCP
             negotiation, unless the ipcp-accept-local and/or
             ipcp-accept-remote options are given, respectively.

     bsdcomp nr,nt
             Request that the peer compress packets that it sends, using the
             BSD-Compress scheme, with a maximum code size of nr bits, and
             agree to compress packets sent to the peer with a maximum code
             size of nt bits.  If nt is not specified, it defaults to the
             value given for nr.  Values in the range 9 to 15 may be used for
             nr and nt; larger values give better compression but consume more
             kernel memory for compression dictionaries.  Alternatively, a
             value of 0 for nr or nt disables compression in the corresponding
             direction.  nobsdcomp or bsdcomp 0 disables BSD-Compress
             compression entirely.

     chap-interval n
             If this option is given, pppd will rechallenge the peer every n
             seconds.

     chap-max-challenge n
             Set the maximum number of CHAP challenge transmissions to n
             (default 10).

     chap-restart n
             Set the CHAP restart interval (retransmission timeout for
             challenges) to n seconds (default 3).

     debug   Enables connection debugging facilities.  If this option is
             given, pppd will log the contents of all control packets sent or
             received in a readable form.  The packets are logged through
             syslogd(8) with facility daemon and level debug.  This
             information can be directed to a file by setting up
             /etc/syslog.conf appropriately (see syslog.conf(5)).

     default-asyncmap
             Disable asyncmap negotiation, forcing all control characters to
             be escaped for both the transmit and the receive direction.

     default-mru
             Disable MRU (Maximum Receive Unit) negotiation.  With this
             option, pppd will use the default MRU value of 1500 bytes for
             both the transmit and receive direction.

     deflate nr,nt
             Request that the peer compress packets that it sends, using the
             Deflate scheme, with a maximum window size of 2**nr bytes, and
             agree to compress packets sent to the peer with a maximum window
             size of 2**nt bytes.  If nt is not specified, it defaults to the
             value given for nr.  Values in the range 8 to 15 may be used for
             nr and nt; larger values give better compression but consume more
             kernel memory for compression dictionaries.  Alternatively, a
             value of 0 for nr or nt disables compression in the corresponding
             direction.  Use nodeflate or deflate 0 to disable Deflate
             compression entirely.  (Note: pppd requests Deflate compression
             in preference to BSD-Compress if the peer can do either.)

     demand  Initiate the link only on demand, i.e., when data traffic is
             present.  With this option, the remote IP address must be
             specified by the user on the command line or in an options file.
             pppd will initially configure the interface and enable it for IP
             traffic without connecting to the peer.  When traffic is
             available, pppd will connect to the peer and perform negotiation,
             authentication, etc.  When this is completed, pppd will commence
             passing data packets (i.e., IP packets) across the link.

             The demand option implies the persist option.  If this behaviour
             is not desired, use the nopersist option after the demand option.
             The idle and holdoff options are also useful in conjunction with
             the demand option.

     domain d
             Append the domain name d to the local host name for
             authentication purposes.  For example, if gethostname(3) returns
             the name porsche, but the fully qualified domain name is
             porsche.Quotron.COM, you could specify domain Quotron.COM.  pppd
             would then use the name porsche.Quotron.COM for looking up
             secrets in the secrets file, and as the default name to send to
             the peer when authenticating itself to the peer.  This option is
             privileged.

     holdoff n
             Specifies how many seconds to wait before re-initiating the link
             after it terminates.  This option only has any effect if the
             persist or demand option is used.  The holdoff period is not
             applied if the link was terminated because it was idle.

     idle n  Specifies that pppd should disconnect if the link is idle for n
             seconds.  The link is idle when no data packets (i.e., IP
             packets) are being sent or received.  Note: it is not advisable
             to use this option with the persist option without the demand
             option.  If the active-filter option is given, data packets which
             are rejected by the specified activity filter also count as the
             link being idle.

     ipcp-accept-local
             With this option, pppd will accept the peer's idea of our local
             IP address, even if the local IP address was specified in an
             option.

     ipcp-accept-remote
             With this option, pppd will accept the peer's idea of its
             (remote) IP address, even if the remote IP address was specified
             in an option.

     ipcp-max-configure n
             Set the maximum number of IPCP configure-request transmissions to
             n (default 10).

     ipcp-max-failure n
             Set the maximum number of IPCP configure-NAKs returned before
             starting to send configure-Rejects to n (default 10).

     ipcp-max-terminate n
             Set the maximum number of IPCP terminate-request transmissions to
             n (default 3).

     ipcp-restart n
             Set the IPCP restart interval (retransmission timeout) to n
             seconds (default 3).

     ipparam string
             Provides an extra parameter to the ip-up and ip-down scripts.  If
             this option is given, the string supplied is given as the 6th
             parameter to those scripts.

     kdebug n
             Enable debugging code in the kernel-level PPP driver.  The
             argument n is a number which is the sum of the following values:
             1 to enable general debug messages, 2 to request that the
             contents of received packets be printed, and 4 to request that
             the contents of transmitted packets be printed.  On most systems,
             messages printed by the kernel are logged by syslogd(8) to a file
             as directed in the /etc/syslog.conf configuration file.

     lcp-echo-failure n
             If this option is given, pppd will presume the peer to be dead if
             n LCP echo-requests are sent without receiving a valid LCP echo-
             reply.  If this happens, pppd will terminate the connection.  Use
             of this option requires a non-zero value for the
             lcp-echo-interval parameter.  This option can be used to enable
             pppd to terminate after the physical connection has been broken
             (e.g., the modem has hung up) in situations where no hardware
             modem control lines are available.

     lcp-echo-interval n
             If this option is given, pppd will send an LCP echo-request frame
             to the peer every n seconds.  Normally the peer should respond to
             the echo-request by sending an echo-reply.  This option can be
             used with the lcp-echo-failure option to detect that the peer is
             no longer connected.

     lcp-max-configure n
             Set the maximum number of LCP configure-request transmissions to
             n (default 10).

     lcp-max-failure n
             Set the maximum number of LCP configure-NAKs returned before
             starting to send configure-Rejects to n (default 10).

     lcp-max-terminate n
             Set the maximum number of LCP terminate-request transmissions to
             n (default 3).

     lcp-restart n
             Set the LCP restart interval (retransmission timeout) to n
             seconds (default 3).

     local   Don't use the modem control lines.  With this option, pppd will
             ignore the state of the CD (Carrier Detect) signal from the modem
             and will not change the state of the DTR (Data Terminal Ready)
             signal.

     login   Use the system password database for authenticating the peer
             using PAP, and record the user in the system wtmp file.  Note
             that the peer must have an entry in the /etc/ppp/pap-secrets file
             as well as the system password database to be allowed access.

     maxconnect n
             Terminate the connection when it has been available for network
             traffic for n seconds (i.e., n seconds after the first network
             control protocol comes up).

     modem   Use the modem control lines.  This option is the default.  With
             this option, pppd will wait for the CD (Carrier Detect) signal
             from the modem to be asserted when opening the serial device
             (unless a connect script is specified), and it will drop the DTR
             (Data Terminal Ready) signal briefly when the connection is
             terminated and before executing the connect script.  On Ultrix,
             this option implies hardware flow control, as for the crtscts
             option.

     modem_chat
             Use the modem control lines during the chat script.  The default
             is to ignore the state of the CD (Carrier Detect) signal from the
             modem during the chat script.  If you are using a cua(4) device
             (as opposed to a tty(4) device) you should set this option.  You
             should not use this option with a dialback setup as it will cause
             the chat script to exit when carrier drops.

     ms-dns [addr]
             If pppd is acting as a server for Microsoft Windows clients, this
             option allows pppd to supply one or two DNS (Domain Name Server)
             addresses to the clients.  The first instance of this option
             specifies the primary DNS address; the second instance (if given)
             specifies the secondary DNS address.  (This option was present in
             some older versions of pppd under the name dns-addr.)

     ms-wins [addr]
             If pppd is acting as a server for Microsoft Windows or "Samba"
             clients, this option allows pppd to supply one or two WINS
             (Windows Internet Name Services) server addresses to the clients.
             The first instance of this option specifies the primary WINS
             address; the second instance (if given) specifies the secondary
             WINS address.

     name name
             Set the name of the local system for authentication purposes to
             name.  This is a privileged option.  With this option, pppd will
             use lines in the secrets files which have name as the second
             field when looking for a secret to use in authenticating the
             peer.  In addition, unless overridden with the user option, name
             will be used as the name to send to the peer when authenticating
             the local system to the peer.  (Note that pppd does not append
             the domain name to name.)

     netmask n
             Set the interface netmask to n, a 32-bit netmask in "decimal dot"
             notation (e.g. 255.255.255.0).  If this option is given, the
             value specified is ORed with the default netmask.  The default
             netmask is chosen based on the negotiated remote IP address; it
             is the appropriate network mask for the class of the remote IP
             address, ORed with the netmasks for any non point-to-point
             network interfaces in the system which are on the same network.
             (Note: on some platforms, pppd will always use 255.255.255.255
             for the netmask, if that is the only appropriate value for a
             point-to-point interface.)

     noaccomp
             Disable Address/Control compression in both directions (send and
             receive).

     noauth  Do not require the peer to authenticate itself.  This option is
             privileged if the auth option is specified in /etc/ppp/options.

     nobsdcomp
             Disables BSD-Compress compression; pppd will not request or agree
             to compress packets using the BSD-Compress scheme.

     noccp   Disable CCP (Compression Control Protocol) negotiation.  This
             option should only be required if the peer is buggy and gets
             confused by requests from pppd for CCP negotiation.

     nocrtscts
             Disable hardware flow control (i.e., RTS/CTS) on the serial port.
             If neither the crtscts nor the nocrtscts option is given, the
             hardware flow control setting for the serial port is left
             unchanged.

     nodefaultroute
             Disable the defaultroute option.  The system administrator who
             wishes to prevent users from creating default routes with pppd
             can do so by placing this option in the /etc/ppp/options file.

     nodeflate
             Disables Deflate compression; pppd will not request or agree to
             compress packets using the Deflate scheme.

     nodetach
             Don't detach from the controlling terminal.  Without this option,
             if a serial device other than the terminal on the standard input
             is specified, pppd will fork to become a background process.

     noip    Disable IPCP negotiation and IP communication.  This option
             should only be required if the peer is buggy and gets confused by
             requests from pppd for IPCP negotiation.

     noipdefault
             Disables the default behaviour when no local IP address is
             specified, which is to determine (if possible) the local IP
             address from the hostname.  With this option, the peer will have
             to supply the local IP address during IPCP negotiation (unless it
             was specified explicitly on the command line or in an options
             file).

     nomagic
             Disable magic number negotiation.  With this option, pppd cannot
             detect a looped-back line.  This option should only be needed if
             the peer is buggy.

     nopcomp
             Disable protocol field compression negotiation in both the
             receive and the transmit direction.

     nopersist
             Exit once a connection has been made and terminated.  This is the
             default unless the persist or demand option has been specified.

     nopredictor1
             Do not accept or agree to Predictor-1 compression.

     noproxyarp
             Disable the proxyarp option.  The system administrator who wishes
             to prevent users from creating proxy ARP entries with pppd can do
             so by placing this option in the /etc/ppp/options file.

     novj    Disable Van Jacobson style TCP/IP header compression in both the
             transmit and the receive direction.

     novjccomp
             Disable the connection-ID compression option in Van Jacobson
             style TCP/IP header compression.  With this option, pppd will not
             omit the connection-ID byte from Van Jacobson compressed TCP/IP
             headers, nor ask the peer to do so.

     papcrypt
             Indicates that all secrets in the /etc/ppp/pap-secrets file which
             are used for checking the identity of the peer are encrypted, and
             thus pppd should not accept a password which, before encryption,
             is identical to the secret from the /etc/ppp/pap-secrets file.

     pap-max-authreq n
             Set the maximum number of PAP authenticate-request transmissions
             to n (default 10).

     pap-restart n
             Set the PAP restart interval (retransmission timeout) to n
             seconds (default 3).

     pap-timeout n
             Set the maximum time that pppd will wait for the peer to
             authenticate itself with PAP to n seconds (0 means no limit).

     pass-filter filter-expression
             Specifies a packet filter to apply to data packets being sent or
             received to determine which packets should be allowed to pass.
             Packets which are rejected by the filter are silently discarded.
             This option can be used to prevent specific network protocols
             using up link bandwidth, or to provide a basic firewall
             capability.  The filter-expression syntax is as described for
             tcpdump(8), except that qualifiers which are inappropriate for a
             PPP link, such as ether and arp, are not permitted.  Generally
             the filter expression should be enclosed in single quotes to
             prevent whitespace in the expression from being interpreted by
             the shell.  Note that it is possible to apply different
             constraints to incoming and outgoing packets using the inbound
             and outbound qualifiers.

     persist
             Do not exit after a connection is terminated; instead try to
             reopen the connection.

     predictor1
             Request that the peer compress frames that it sends using
             Predictor-1 compression, and agree to compress transmitted frames
             with Predictor-1 if requested.  This option has no effect unless
             the kernel driver supports Predictor-1 compression.

     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.  This will have the effect of making the peer appear
             to other systems to be on the local Ethernet.

     remotename name
             Set the assumed name of the remote system for authentication
             purposes to name.

     refuse-chap
             With this option, pppd will not agree to authenticate itself to
             the peer using CHAP.

     refuse-pap
             With this option, pppd will not agree to authenticate itself to
             the peer using PAP.

     require-chap
             Require the peer to authenticate itself using CHAP (Challenge
             Handshake Authentication Protocol) authentication.

     require-pap
             Require the peer to authenticate itself using PAP (Password
             Authentication Protocol) authentication.

     silent  With this option, 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 ancient versions of pppd).

     usehostname
             Enforce the use of the hostname (with domain name appended, if
             given) as the name of the local system for authentication
             purposes (overrides the name option).

     user name
             Sets the name used for authenticating the local system to the
             peer to name.

     vj-max-slots n
             Sets the number of connection slots to be used by the Van
             Jacobson TCP/IP header compression and decompression code to n,
             which must be between 2 and 16, inclusive.

     welcome script
             Run the executable or shell command specified by script before
             initiating PPP negotiation, after the connect script (if any) has
             completed.  This option is privileged if the noauth option is
             used.

     xonxoff
             Use software flow control (i.e., XON/XOFF) to control the flow of
             data on the serial port.


OPTIONS FILES

     Options can be taken from files as well as the command line.  pppd reads
     options from the files /etc/ppp/options, ~/.ppprc and
     /etc/ppp/options.ttyname (in that order) before processing the options on
     the command line.  (In fact, the command-line options are scanned to find
     the terminal name before the options.ttyname file is read.)  In forming
     the name of the options.ttyname file, the initial /dev/ is removed from
     the terminal name, and any remaining / characters are replaced with dots.

     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 double-quotes (").  A backslash (\) quotes the following character.  A
     hash (#) starts a comment, which continues until the end of the line.
     There is no restriction on using the file or call options within an
     options file.


SECURITY

     Users must be in group "network" to be able to use pppd.

     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 restrict the ways in which pppd
     can be used, 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.

     The normal way that pppd should be set up is to have the auth option in
     the /etc/ppp/options file.  (This may become the default in later
     releases.)  If users wish to use pppd to dial out to a peer which will
     refuse to authenticate itself (such as an internet service provider), the
     system administrator should create an options file under /etc/ppp/peers
     containing the noauth option, the name of the serial port to use, and the
     connect option (if required), plus any other appropriate options.  In
     this way, pppd can be set up to allow non-privileged users to make
     unauthenticated connections only to trusted peers.

     As indicated above, some security-sensitive options are privileged, which
     means that they may not be used by an ordinary non-privileged user
     running a setuid-root pppd, either on the command line, in the user's
     ~/.ppprc file, or in an options file read using the file option.
     Privileged options may be used in the /etc/ppp/options file or in an
     options file read using the call option.  If pppd is being run by the
     root user, privileged options can be used without restriction.


AUTHENTICATION

     Authentication is the process whereby one peer convinces the other of its
     identity.  This involves the first peer sending its name to the other,
     together with some kind of secret information which could only come from
     the genuine authorized user of that name.  In such an exchange, we will
     call the first peer the "client" and the other the "server".  The client
     has a name by which it identifies itself to the server, and the server
     also has a name by which it identifies itself to the client.  Generally
     the genuine client shares some secret (or password) with the server, and
     authenticates itself by proving that it knows that secret.  Very often,
     the names used for authentication correspond to the internet hostnames of
     the peers, but this is not essential.

     At present, pppd supports two authentication protocols: the Password
     Authentication Protocol (PAP) and the Challenge Handshake Authentication
     Protocol (CHAP).  PAP involves the client sending its name and a
     cleartext password to the server to authenticate itself.  In contrast,
     the server initiates the CHAP authentication exchange by sending a
     challenge to the client (the challenge packet includes the server's
     name).  The client must respond with a response which includes its name
     plus a hash value derived from the shared secret and the challenge, in
     order to prove that it knows the secret.

     The PPP protocol, being symmetrical, allows both peers to require the
     other to authenticate itself.  In that case, two separate and independent
     authentication exchanges will occur.  The two exchanges could use
     different authentication protocols, and in principle, different names
     could be used in the two exchanges.

     The default behaviour of pppd is to agree to authenticate if requested,
     and to not require authentication from the peer.  However, pppd will not
     agree to authenticate itself with a particular protocol if it has no
     secrets which could be used to do so.

     pppd stores secrets for use in authentication in secrets files
     (/etc/ppp/pap-secrets for PAP, /etc/ppp/chap-secrets for CHAP).  Both
     secrets files have the same format.  The secrets files can contain
     secrets for pppd to use in authenticating itself to other systems, as
     well as secrets for pppd to use when authenticating other systems to
     itself.

     Each line in a secrets file contains one 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, or if the first word is
     "-", then all IP addresses are disallowed.  To allow any address, use
     "*".  A word starting with "!" indicates that the specified address is
     not acceptable.  An address may be followed by "/" and a number n, to
     indicate a whole subnet, i.e., all addresses which have the same value in
     the most significant n bits.  Case is significant in the client and
     server names and in the secret.

     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, pppd takes the best
     match, i.e., the match with the fewest wildcards.

     Thus a secrets file contains both secrets for use in authenticating other
     hosts, plus secrets which we use for authenticating ourselves to others.
     When pppd is authenticating the peer (checking the peer's identity), it
     chooses a secret with the peer's name in the first field and the name of
     the local system in the second field.  The name of the local system
     defaults to the hostname, with the domain name appended if the domain
     option is used.  This default can be overridden with the name option,
     except when the usehostname option is used.

     When pppd is choosing a secret to use in authenticating itself to the
     peer, it first determines what name it is going to use to identify itself
     to the peer.  This name can be specified by the user with the user
     option.  If this option is not used, the name defaults to the name of the
     local system, determined as described in the previous paragraph.  Then
     pppd looks for a secret with this name in the first field and the peer's
     name in the second field.  pppd will know the name of the peer if CHAP
     authentication is being used, because the peer will have sent it in the
     challenge packet.  However, if PAP is being used, pppd will have to
     determine the peer's name from the options specified by the user.  The
     user can specify the peer's name directly with the remotename option.
     Otherwise, if the remote IP address was specified by a name (rather than
     in numeric form), that name will be used as the peer's name.  Failing
     that, pppd will use the null string as the peer's name.

     When authenticating the peer with PAP, the supplied password is first
     compared with the secret from the secrets file.  If the password doesn't
     match the secret, the password is encrypted using crypt(3) and checked
     against the secret again.  Thus secrets for authenticating the peer can
     be stored in encrypted form if desired.  If the papcrypt option is given,
     the first (unencrypted) comparison is omitted, for better security.

     Furthermore, if the login 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.  Typically, when using the login option, the secret in
     /etc/ppp/pap-secrets would be (), which will match any password supplied
     by the peer.  This avoids the need to have the same secret in two places.

     Authentication must be satisfactorily completed before IPCP (or any other
     Network Control Protocol) can be started.  If the peer is required to
     authenticate itself, and fails to do so, pppd will terminate 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.

     In some cases it is desirable to allow some hosts which can't
     authenticate themselves to connect and use one of a restricted set of IP
     addresses, even when the local host generally requires authentication.
     If the peer refuses to authenticate itself when requested, pppd takes
     that as equivalent to authenticating with PAP using the empty string for
     the username and password.  Thus, by adding a line to the pap-secrets
     file which specifies the empty string for the client and password, it is
     possible to allow restricted access to hosts which refuse to authenticate
     themselves.


ROUTING

     When IPCP negotiation is completed successfully, 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 most cases the defaultroute
     and/or proxyarp options are sufficient for this, but in some cases
     further intervention is required.  The /etc/ppp/ip-up script can be used
     for this.

     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 defaultroute option causes pppd to create
     such a default route when IPCP comes up, and delete it when the link is
     terminated.

     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 proxyarp option causes pppd 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, pppd creates a permanent, published ARP
     entry with the IP address of the remote host and the hardware address of
     the network interface found.

     When the demand option is used, the interface IP addresses have already
     been set at the point when IPCP comes up.  If pppd has not been able to
     negotiate the same addresses that it used to configure the interface (for
     example when the peer is an ISP that uses dynamic IP address assignment),
     pppd has to change the interface IP addresses to the negotiated
     addresses.  This may disrupt existing connections, and the use of demand
     dialling with peers that do dynamic IP address assignment is not
     recommended.


SCRIPTS

     pppd invokes scripts at various stages in its processing which can be
     used to perform site-specific ancillary processing.  These scripts are
     usually shell scripts, but could be executable code files instead.  pppd
     does not wait for the scripts to finish.  pppd runs the scripts with
     standard input, output and error redirected to /dev/null, and with an
     environment that is empty except for some environment variables that give
     information about the link.  The environment variables that pppd sets
     are:

     DEVICE    The name of the serial tty device being used.

     IFNAME    The name of the network interface being used.

     IPLOCAL   The IP address for the local end of the link.  This is only set
               when IPCP has come up.

     IPREMOTE  The IP address for the remote end of the link.  This is only
               set when IPCP has come up.

     PEERNAME  The authenticated name of the peer.  This is only set if the
               peer authenticates itself.

     SPEED     The baud rate of the tty device.

     UID       The real user ID of the user who invoked pppd.

     pppd invokes the following scripts, if they exist.  It is not an error if
     they don't exist.

     /etc/ppp/auth-up
             A program or script which is executed after the remote system
             successfully authenticates itself.  It is executed with the
             parameters

             interface-name peer-name user-name tty-device speed

             Note that this script is not executed if the peer doesn't
             authenticate itself, for example when the noauth option is used.

     /etc/ppp/auth-down
             A program or script which is executed when the link goes down, if
             /etc/ppp/auth-up was previously executed.  It is executed in the
             same manner with the same parameters as /etc/ppp/auth-up.

     /etc/ppp/ip-up
             A program or script which is executed when the link is available
             for sending and receiving IP packets (that is, IPCP has come up).
             It is executed with the parameters

             interface-name tty-device speed local-IP-address
             remote-IP-address ipparam

     /etc/ppp/ip-down
             A program or script which is executed when the link is no longer
             available for sending and receiving IP packets.  This script can
             be used for undoing the effects of the /etc/ppp/ip-up script.  It
             is invoked in the same manner and with the same parameters as the
             ip-up script.


FILES

     /etc/ppp/pap-secrets
             Usernames, passwords and IP addresses for PAP authentication.
             This file should be owned by root and not readable or writable by
             any other user.  pppd will log a warning if this is not the case.

     /etc/ppp/chap-secrets
             Names, secrets and IP addresses for CHAP authentication.  As for
             /etc/ppp/pap-secrets, this file should be owned by root and not
             readable or writable by any other user.  pppd will log a warning
             if this is not the case.

     /etc/ppp/options
             System default options for pppd, read before user default options
             or command-line options.

     ~/.ppprc
             User default options, read before /etc/ppp/options.ttyname.

     /etc/ppp/options.ttyname
             System default options for the serial port being used, read after
             ~/.ppprc.  In forming the ttyname part of this filename, an
             initial /dev/ is stripped from the port name (if present), and
             any slashes in the remaining part are converted to dots.

     /etc/ppp/peers
             A directory containing options files which may contain privileged
             options, even if pppd was invoked by a user other than root.  The
             system administrator can create options files in this directory
             to permit non-privileged users to dial out without requiring the
             peer to authenticate, but only to certain trusted peers.


EXAMPLES

     The following examples assume that the /etc/ppp/options file contains the
     auth option (as in the default /etc/ppp/options file in the PPP
     distribution).

     Probably the most common use of pppd is to dial out to an ISP.  This can
     be done with a command such as

           pppd call isp

     where the /etc/ppp/peers/isp file is set up by the system administrator
     to contain something like this:

           ttyS0 19200 crtscts
           connect '/usr/sbin/chat -v -f /etc/ppp/chat-isp'
           noauth

     In this example, we are using chat to dial the ISP's modem and go through
     any logon sequence required.  The /etc/ppp/chat-isp file contains the
     script used by chat; it could for example contain something like this:

           ABORT "NO CARRIER"
           ABORT "NO DIALTONE"
           ABORT "ERROR"
           ABORT "NO ANSWER"
           ABORT "BUSY"
           ABORT "Username/Password Incorrect"
           "" "at"
           OK "at&d0&c1"
           OK "atdt2468135"
           "name:" "^Umyuserid"
           "word:" "\qmypassword"
           "ispts" "\q^Uppp"
           "~-^Uppp-~"

     See the chat(8) man page for details of chat scripts.

     pppd can also be used to provide a dial-in PPP service for users.  If the
     users already have login accounts, the simplest way to set up the PPP
     service is to let the users log in to their accounts and run pppd
     (installed setuid-root) with a command such as

           pppd proxyarp

     To allow a user to use the PPP facilities, you need to allocate an IP
     address for that user's machine and create an entry in
     /etc/ppp/pap-secrets or /etc/ppp/chap-secrets (depending on which
     authentication method the PPP implementation on the user's machine
     supports), so that the user's machine can authenticate itself.  For
     example, if Joe has a machine called "joespc" which is to be allowed to
     dial in to the machine called "server" and use the IP address
     joespc.my.net, you would add an entry like this to /etc/ppp/pap-secrets
     or /etc/ppp/chap-secrets:

           joespc    server    "joe's secret" joespc.my.net

     Alternatively, you can create a username called (for example) "ppp",
     whose login shell is pppd and whose home directory is /etc/ppp.  Options
     to be used when pppd is run this way can be put in /etc/ppp/.ppprc.

     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
     asyncmap a0000.  If the path includes a telnet, you probably should
     escape ^] as well (asyncmap 200a0000).  If the path includes an rlogin,
     you will need to use the escape ff option on the end which is running the
     rlogin client, since many rlogin implementations are not transparent;
     they will remove the sequence (0xff, 0xff, 0x73, 0x73, followed by any 8
     bytes) from the stream.


DIAGNOSTICS

     Messages are sent to the syslogd(8) daemon using facility LOG_DAEMON.
     (This can be overridden by recompiling pppd with the macro LOG_PPP
     defined as the desired facility.)  See the syslogd(8) documentation for
     details of where the syslog daemon will write the messages.  On most
     systems, the syslog daemon uses the /etc/syslog.conf file to specify the
     destination(s) for syslog messages.  You may need to edit that file to
     suit.

     The debug option causes the contents of all control packets sent or
     received to be logged, that is, all LCP, PAP, CHAP or IPCP packets.  This
     can be useful if the PPP negotiation does not succeed or if
     authentication fails.  If debugging is enabled at compile time, the debug
     option also causes other debugging messages to be logged.

     Debugging can also be enabled or disabled by sending a SIGUSR1 signal to
     the pppd process.  This signal acts as a toggle.


SEE ALSO

     cua(4), ppp(4), tty(4), chat(8), syslogd(8), tcpdump(8)

     V. Jacobson, Compressing TCP/IP Headers for Low-Speed Serial Links, RFC
     1144, February 1990.

     R. Rivest, The MD5 Message-Digest Algorithm, RFC 1321, April 1992.

     G. McGregor, The PPP Internet Protocol Control Protocol (IPCP), RFC 1332,
     May 1992.

     B. Lloyd and W. Simpson, PPP Authentication Protocols, RFC 1334, October
     1992.

     W. Simpson, The Point-to-Point Protocol (PPP), RFC 1661, July 1994.

     W. Simpson, PPP in HDLC-like Framing, RFC 1662, July 1994.

     W. Simpson, PPP Challenge Handshake Authentication Protocol (CHAP), RFC
     1994, August 1996.


NOTES

     Some limited degree of control can be exercised over a running pppd
     process by sending it a signal from the list below.

     SIGINT, SIGTERM
             These signals cause pppd to terminate the link (by closing LCP),
             restore the serial device settings, and exit.

     SIGHUP  This signal causes pppd to terminate the link, restore the serial
             device settings, and close the serial device.  If the persist or
             demand option has been specified, pppd will try to reopen the
             serial device and start another connection (after the holdoff
             period).  Otherwise pppd will exit.  If this signal is received
             during the holdoff period, it causes pppd to end the holdoff
             period immediately.

     SIGUSR1
             This signal toggles the state of the debug option.

     SIGUSR2
             This signal causes pppd to renegotiate compression.  This can be
             useful to re-enable compression after it has been disabled as a
             result of a fatal decompression error.  (Fatal decompression
             errors generally indicate a bug in one or other implementation.)


AUTHORS

     Paul Mackerras <Paul.Mackerras@samba.org>, based on earlier work by Drew
     Perkins, Brad Clements, Karl Fox, Greg Christy, and Brad Parker.


BUGS

     Scripts should be run as root, but are not.

OpenBSD 6.2                    October 28, 2015                    OpenBSD 6.2

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