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

NAME
       pppd - Point to Point Protocol daemon

SYNOPSIS
       pppd [ tty_name ] [ speed ] [ options ]

DESCRIPTION
       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.

       The encapsulation scheme is provided by driver code in the kernel.
       Pppd provides the basic LCP, authentication support, and an NCP for
       establishing and configuring the Internet Protocol (IP) (called the IP
       Control Protocol, IPCP).

FREQUENTLY USED OPTIONS
       _tty_name_
              Communicate over the named device.  The string "/dev/" is
              prepended if necessary.  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_
              Set the baud rate to <speed> (a decimal number).  On systems
              such as 4.4BSD and NetBSD, any speed can be specified, providing
              that it is supported by the serial device driver.  Other systems
              (e.g. SunOS, Linux) allow only a limited set of speeds.

       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(1), 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.  This option only available if
              both the kernel and pppd were compiled with PPP_FILTER defined.

       asyncmap _map_
              Set the async character map to <map>.  This map describes which
              control characters cannot be successfully received over the
              serial line.  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 ^_.  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
              Use the executable or shell command specified by script to set
              up the serial line.  This script would typically use the chat(8)
              program to dial the modem and start the remote ppp session.
              This option is privileged if the noauth option is used.

       connect-max-attempts _n_
              Attempt dial-out connection to remote system no more than
              specified number of times (default = 1).  If the connection is
              not made, pppd will exit.  Requires that persist has been
              specified.

       crtscts
              Use hardware flow control (i.e. RTS/CTS) to control the flow of
              data 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.

       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
              Run the executable or shell command specified by script after
              pppd has terminated the link.  This script 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 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).

       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.

       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.  Use nobsdcomp or bsdcomp 0 to disable
              BSD-Compress compression entirely.

       callback phone_number
              Request a call-back to the phone_number.  This only works if the
              peer is speaking the Call Back Configuration Protocol.  Do not
              put this into the main options file if you sometimes connect to
              servers that don't support it.

       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
              syslog 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() 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 instead 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.

       ipx    Enable the IPXCP and IPX protocols.  This option is presently
              only supported under Linux, and only if your kernel has been
              configured to include IPX support.

       ipx-network n
              Set the IPX network number in the IPXCP configure request frame
              to n, a hexadecimal number (without a leading 0x).  There is no
              valid default.  If this option is not specified, the network
              number is obtained from the peer.  If the peer does not have the
              network number, the IPX protocol will not be started.

       ipx-node n:m
              Set the IPX node numbers.  The two node numbers are separated
              from each other with a colon character.  The first number n is
              the local node number.  The second number m is the peer's node
              number.  Each node number is a hexadecimal number, at most 10
              digits long.  The node numbers on the ipx-network must be
              unique.  There is no valid default.  If this option is not
              specified then the node numbers are obtained from the peer.

       ipx-router-name _string_
              Set the name of the router.  This is a string and is sent to the
              peer as information data.

       ipx-routing n
              Set the routing protocol to be received by this option.  More
              than one instance of ipx-routing may be specified.  The 'none'
              option (0) may be specified as the only instance of ipx-routing.
              The values may be 0 for NONE, 2 for RIP/SAP, and 4 for NLSP.

       ipxcp-accept-local
              Accept the peer's NAK for the node number specified in the ipx-
              node option.  If a node number was specified, and non-zero, the
              default is to insist that the value be used.  If you include
              this option then you will permit the peer to override the entry
              of the node number.

       ipxcp-accept-network
              Accept the peer's NAK for the network number specified in the
              ipx-network option.  If a network number was specified, and non-
              zero, the default is to insist that the value be used.  If you
              include this option then you will permit the peer to override
              the entry of the node number.

       ipxcp-accept-remote
              Use the peer's network number specified in the configure request
              frame.  If a node number was specified for the peer and this
              option was not specified, the peer will be forced to use the
              value which you have specified.

       ipxcp-max-configure n
              Set the maximum number of IPXCP configure request frames which
              the system will send to n.  The default is 10.

       ipxcp-max-failure n
              Set the maximum number of IPXCP NAK frames which the local
              system will send before it rejects the options.  The default
              value is 3.

       ipxcp-max-terminate n
              Set the maximum number of IPXCP terminate request frames before
              the local system considers that the peer is not listening to
              them.  The default value is 3.

       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 syslog(1)
              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 instead 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.

       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.

       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 specified explicitly on the command line or in an options
              file).

       noipx  Disable the IPXCP and IPX protocols.  This option should only be
              required if the peer is buggy and gets confused by requests from
              pppd for IPXCP negotiation.

       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 applied 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
              daemons (such as routed) using up link bandwidth, or to provide
              a basic firewall capability.  The filter-expression syntax is as
              described for tcpdump(1), 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.  This option is
              currently only available under NetBSD, and then only if both the
              kernel and pppd were compiled with PPP_FILTER defined.

       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
       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 /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.  A given secret is
       specific to a particular combination of client and server - it can only
       be used by that client to authenticate itself to that server.  Thus
       each line in a secrets file has at least 3 fields: the name of the
       client, the name of the server, and the secret.  These fields may be
       followed by a list of the IP addresses that the specified client may
       use when connecting to the specified server.

       A secrets file is parsed into words as for an options file, so the
       client name, server name and secrets fields must each be one word, with
       any embedded spaces or other special characters quoted or escaped.  Any
       following words on the same line are taken to be a list of acceptable
       IP addresses for that client, or an override for "local:remote"
       addresses (the same format used on the command line or in the options
       file) when on a line that contains a specific client name (not a
       wildcard nor empty).  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.  Note that 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() 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.

       Additional checks are performed when the login option is used.  If the
       file /etc/ppp/ppp.deny exists, and the user is listed in it, the
       authentication fails.  If the file /etc/ppp/ppp.shells exists and the
       user's normal login shell is not listed, the authentication fails.

       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
       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.

       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.

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 syslog daemon using facility LOG_DAEMON.
       (This can be overriden by recompiling pppd with the macro LOG_PPP
       defined as the desired facility.)  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.

       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.

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.  The scripts are executed
       as root (with the real and effective user-id set to 0), so that they
       can do things such as update routing tables or run privileged daemons.
       Be careful that the contents of these scripts do not compromise your
       system's security.  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.

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

              interface-name tty-device speed network-number local-IPX-node-
              address remote-IPX-node-address local-IPX-routing-protocol
              remote-IPX-routing-protocol local-IPX-router-name remote-IPX-
              router-name ipparam pppd-pid

              The local-IPX-routing-protocol and remote-IPX-routing-protocol
              field may be one of the following:

              NONE      to indicate that there is no routing protocol
              RIP       to indicate that RIP/SAP should be used
              NLSP      to indicate that Novell NLSP should be used
              RIP NLSP  to indicate that both RIP/SAP and NLSP should be used

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

FILES
       /var/run/pppn.pid (BSD or Linux), /etc/ppp/pppn.pid (others)
              Process-ID for pppd process on ppp interface unit n.

       /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.

       /etc/ppp/ppp.deny
              Lists users who may not use the system password PAP
              authentication.

       /etc/ppp/ppp.shells
              Lists user shells which are approved for system password PAP
              authentication logins.

       /usr/share/examples/pppd/
              Sample pppd configuration files.

SEE ALSO
       chat(8), ppp(8)

       RFC1144
              Jacobson, V.  Compressing TCP/IP headers for low-speed serial
              links. February 1990.

       RFC1321
              Rivest, R.  The MD5 Message-Digest Algorithm.  April 1992.

       RFC1332
              McGregor, G.  PPP Internet Protocol Control Protocol (IPCP).
              May 1992.

       RFC1334
              Lloyd, B.; Simpson, W.A.  PPP authentication protocols.  October
              1992.

       RFC1661
              Simpson, W.A.  The Point-to-Point Protocol (PPP).  July 1994.

       RFC1662
              Simpson, W.A.  PPP in HDLC-like Framing.  July 1994.

NOTES
       The following signals have the specified effect when sent to pppd.

       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@cs.anu.edu.au), based on earlier work by
       Drew Perkins, Brad Clements, Karl Fox, Greg Christy, and Brad Parker.

                                                                       PPPD(8)

NAME | SYNOPSIS | DESCRIPTION | FREQUENTLY USED OPTIONS | OPTIONS | OPTIONS FILES | SECURITY | AUTHENTICATION | ROUTING | EXAMPLES | DIAGNOSTICS | SCRIPTS | FILES | SEE ALSO | NOTES | AUTHORS

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