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PPPD(8)                                                                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  conjunc-
              tion  with  the  idle  option if there are packets being sent or
              received regularly over the link (for example, routing  informa-
              tion  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 inap-
              propriate for a PPP link, such as ether and arp, are not permit-
              ted.  Generally the filter expression should be enclosed in sin-
              gle-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) rep-
              resents 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 char-
              acters.   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 speci-
              fied 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 spec-
              ified.

       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 transmis-
              sion (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 com-
              mas.  Note that almost any character can be  specified  for  the
              escape option, unlike the asyncmap option which only allows con-
              trol 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 with-
              out 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 corre-
              sponding direction.  Use nobsdcomp or bsdcomp 0 to disable  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 chal-
              lenges) 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  appro-
              priately (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 corre-
              sponding direction.  Use  nodeflate  or  deflate  0  to  disable
              Deflate compression entirely.  (Note: pppd requests Deflate com-
              pression 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 speci-
              fied  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 avail-
              able, 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 conjuc-
              tion with the demand option.

       domain d
              Append  the domain name d to the local host name for authentica-
              tion 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  pack-
              ets)  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 sec-
              onds (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 spec-
              ified 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 sys-
              tem will send before it rejects the options.  The default  value
              is 3.

       ipxcp-max-terminate n
              Set  the  maximum nuber 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 argu-
              ment 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  con-
              tents  of transmitted packets be printed.  On most systems, mes-
              sages 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 connec-
              tion.  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 sec-
              onds (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 ter-
              minated 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 (Win-
              dows 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  stan-
              dard  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 spec-
              ified,  which is to determine (if possible) the local IP address
              from the hostname.  With this option, the peer will have to sup-
              ply  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 speci-
              fied.

       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  sec-
              onds (default 3).

       pap-timeout n
              Set the maximum time that pppd will wait for the peer to authen-
              ticate 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 inap-
              propriate for a PPP link, such as ether and arp, are not permit-
              ted.  Generally the filter expression should be enclosed in sin-
              gle-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 Pre-
              dictor-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 pur-
              poses (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 Jacob-
              son 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  white-
       space.   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  pass-
       word)  with  the  server,  and  authenticates itself by proving that it
       knows that secret.  Very often, the names used for authentication  cor-
       respond  to the internet hostnames of the peers, but this is not essen-
       tial.

       At present, pppd supports two authentication  protocols:  the  Password
       Authentication  Protocol  (PAP) and the Challenge Handshake Authentica-
       tion 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 indepen-
       dent 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  wild-
       card  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 speci-
       fied 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  sig-
       nificant 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 remote-
       name 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 pass-
       word 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  pass-
       word  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 termi-
       nated 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 authenti-
       cate  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  pass-
       word,  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.  Communica-
       tion 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 communi-
       cate 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 nego-
       tiated 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 con-
       tains 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 transpar-
       ent; 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 privi-
              leged 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  authentica-
              tion.

       /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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