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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

       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
       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.

       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  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

       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.

	      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

       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).
	      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.
       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.


       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]
       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.
       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.
       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
       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
       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,

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

	      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.

	      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
       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)

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