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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.

       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
              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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