pppd



PPPD(8)                                                                PPPD(8)




NAME

       pppd - Point-to-Point Protocol Daemon


SYNOPSIS

       pppd [ options ]


DESCRIPTION

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


FREQUENTLY USED OPTIONS

       ttyname
              Use the serial port called ttyname to communicate with the peer.
              The  string  "/dev/" is prepended to ttyname to form the name of
              the device to open.  If no device name is given, or if the  name
              of  the  terminal connected to the standard input is given, pppd
              will use that terminal, and will not fork to put itself  in  the
              background.   A  value  for this option from a privileged source
              cannot be overridden by a non-privileged user.

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

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

       auth   Require the peer to authenticate itself before allowing  network
              packets  to  be sent or received.  This option is the default if
              the system has a default route.  If neither this option nor  the
              noauth option is specified, pppd will only allow the peer to use
              IP addresses to which the system does not already have a  route.

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

       connect script
              Usually there is something which needs to be done to prepare the
              link before the PPP protocol can be started; for instance,  with
              a  dial-up  modem, commands need to be sent to the modem to dial
              the appropriate phone number.  This option specifies an  command
              for pppd to execute (by passing it to a shell) before attempting
              to start PPP negotiation.  The chat (8) program is often  useful
              here,  as it provides a way to send arbitrary strings to a modem
              and respond to received characters.  A  value  for  this  option
              from  a  privileged  source cannot be overridden by a non-privi-
              leged user.

       crtscts
              Specifies that pppd should set the serial port to  use  hardware
              flow  control using the RTS and CTS signals in the RS-232 inter-
              face.  If neither the crtscts, the nocrtscts,  the  cdtrcts  nor
              the nocdtrcts option is given, the hardware flow control setting
              for the serial port is left unchanged.  Some serial ports  (such
              as  Macintosh  serial ports) lack a true RTS output. Such serial
              ports use this mode to implement  unidirectional  flow  control.
              The  serial port will suspend transmission when requested by the
              modem (via CTS) but will be unable to request the modem to  stop
              sending  to  the  computer. This mode retains the ability to use
              DTR as a modem control line.

       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
              Execute the command specified by script,  by  passing  it  to  a
              shell,  after pppd has terminated the link.  This command could,
              for example, issue commands to the modem to cause it to hang  up
              if  hardware modem control signals were not available.  The dis-
              connect script is not run if the modem has already hung  up.   A
              value  for  this option from a privileged source cannot be over-
              ridden by a non-privileged user.

       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.

       init script
              Execute the command specified by script,  by  passing  it  to  a
              shell,  to  initialize the serial line.  This script would typi-
              cally use the chat(8) program to configure the modem  to  enable
              auto  answer.   A value for this option from a privileged source
              cannot be overridden by a non-privileged user.

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

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

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

       passive
              Enables the "passive" option in the LCP.  With this option, pppd
              will  attempt  to initiate a connection; if no reply is received
              from the peer, pppd will then just wait passively  for  a  valid
              LCP  packet from the peer, instead of exiting, as it would 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.

       ipv6 <local_interface_identifier>,<remote_interface_identifier>
              Set the local and/or remote 64-bit interface identifier.  Either
              one may be omitted. The identifier must be specified in standard
              ascii notation of IPv6  addresses  (e.g.  ::dead:beef).  If  the
              ipv6cp-use-ipaddr  option  is given, the local identifier is the
              local IPv4 address (see above).  On  systems  which  supports  a
              unique  persistent  id, such as EUI-48 derived from the Ethernet
              MAC address, ipv6cp-use-persistent option can be used to replace
              the  ipv6  <local>,<remote>  option. Otherwise the identifier is
              randomized.

       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 is currently  only  avail-
              able under Linux, and requires that the kernel was configured to
              include PPP filtering support (CONFIG_PPP_FILTER).  Note that it
              is  possible to apply different constraints to incoming and out-
              going packets using the inbound and outbound qualifiers.

       allow-ip address(es)
              Allow peers to use  the  given  IP  address  or  subnet  without
              authenticating  themselves.  The parameter is parsed as for each
              element of the list of allowed IP addresses in the secrets files
              (see the AUTHENTICATION section below).

       allow-number number
              Allow  peers  to  connect  from  the  given telephone number.  A
              trailing ‘*’ character will match all numbers beginning with the
              leading part.

       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.

       cdtrcts
              Use a non-standard hardware flow control (i.e. DTR/CTS) to  con-
              trol  the  flow  of  data  on  the  serial port.  If neither the
              crtscts, the nocrtscts, the cdtrcts nor the nocdtrcts option  is
              given,  the hardware flow control setting for the serial port is
              left unchanged.  Some serial ports  (such  as  Macintosh  serial
              ports)  lack  a true RTS output. Such serial ports use this mode
              to implement true bi-directional flow control. The sacrifice  is
              that this flow control mode does not permit using DTR as a modem
              control line.

       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).

       connect-delay n
              Wait for up n milliseconds after the connect script finishes for
              a valid PPP packet from the peer.  At the end of this  time,  or
              when  a  valid  PPP  packet is received from the peer, pppd will
              commence negotiation by  sending  its  first  LCP  packet.   The
              default value is 1000 (1 second).  This wait period only applies
              if the connect or pty option is used.

       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 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  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.

       dryrun With the dryrun option, pppd will print out all the option  val-
              ues which have been set and then exit, after parsing the command
              line and options files  and  checking  the  option  values,  but
              before  initiating  the  link.   The option values are logged at
              level info, and also  printed  to  standard  output  unless  the
              device on standard output is the device that pppd would be using
              to communicate with the peer.

       dump   With the dump option, pppd will print out all the option  values
              which  have  been  set.   This  option is like the dryrun option
              except that pppd proceeds as normal rather than exiting.

       endpoint <epdisc>
              Sets the endpoint discriminator sent by the local machine to the
              peer  during  multilink negotiation to <epdisc>.  The default is
              to use the MAC address of the first ethernet  interface  on  the
              system,  if any, otherwise the IPv4 address corresponding to the
              hostname, if any,  provided  it  is  not  in  the  multicast  or
              locally-assigned  IP  address  ranges, or the localhost address.
              The endpoint discriminator can be the string null or of the form
              type:value, where type is a decimal number or one of the strings
              local, IP, MAC, magic, or phone.  The value is an IP address  in
              dotted-decimal notation for the IP type, or a string of bytes in
              hexadecimal, separated by periods or colons for the other types.
              For  the MAC type, the value may also be the name of an ethernet
              or similar network interface.  This  option  is  currently  only
              available under Linux.

       eap-interval n
              If this option is given and pppd authenticates the peer with EAP
              (i.e., is the server),  pppd  will  restart  EAP  authentication
              every  n  seconds.   For EAP SRP-SHA1, see also the srp-interval
              option, which enables lightweight rechallenge.

       eap-max-rreq n
              Set the maximum number  of  EAP  Requests  to  which  pppd  will
              respond  (as  a  client) without hearing EAP Success or Failure.
              (Default is 20.)

       eap-max-sreq n
              Set the maximum number of EAP Requests that pppd will issue  (as
              a server) while attempting authentication.  (Default is 10.)

       eap-restart n
              Set  the  retransmit  timeout  for EAP Requests when acting as a
              server (authenticator).  (Default is 3 seconds.)

       eap-timeout n
              Set the maximum time to wait for the peer to send an EAP Request
              when  acting  as  a client (authenticatee).  (Default is 20 sec-
              onds.)

       hide-password
              When logging the contents of PAP  packets,  this  option  causes
              pppd  to  exclude the password string from the log.  This is the
              default.

       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.

       ipv6cp-max-configure n
              Set the maximum number of IPv6CP configure-request transmissions
              to n (default 10).

       ipv6cp-max-failure n
              Set the maximum number of IPv6CP configure-NAKs returned  before
              starting to send configure-Rejects instead to n (default 10).

       ipv6cp-max-terminate n
              Set the maximum number of IPv6CP terminate-request transmissions
              to n (default 3).

       ipv6cp-restart n
              Set the IPv6CP restart interval (retransmission  timeout)  to  n
              seconds (default 3).

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

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

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

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

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

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

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

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

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

       ipxcp-max-failure n
              Set  the maximum number of IPXCP NAK frames which the local 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 values depend on the specific kernel driver, but in general
              a  value  of 1 will enable general kernel debug messages.  (Note
              that these messages are usually only useful  for  debugging  the
              kernel  driver  itself.)  For the Linux 2.2.x kernel driver, the
              value is a sum of bits: 1 to enable general debug messages, 2 to
              request  that the contents of received packets be printed, and 4
              to request that the contents of transmitted packets be  printed.
              On  most  systems,  messages printed by the kernel are logged by
              syslog(1) to a file as directed in the /etc/syslog.conf configu-
              ration file.

       ktune  Enables  pppd  to  alter  kernel settings as appropriate.  Under
              Linux,   pppd   will   enable   IP    forwarding    (i.e.    set
              /proc/sys/net/ipv4/ip_forward  to  1)  if the proxyarp option is
              used, and will enable the dynamic IP address  option  (i.e.  set
              /proc/sys/net/ipv4/ip_dynaddr  to 1) in demand mode if the local
              address changes.

       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).

       linkname name
              Sets  the  logical name of the link to name.  Pppd will create a
              file named ppp-name.pid in /var/run (or /etc/ppp  on  some  sys-
              tems)  containing  its process ID.  This can be useful in deter-
              mining which instance of pppd is responsible for the link  to  a
              given peer system.  This is a privileged option.

       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.

       logfd n
              Send log messages to file descriptor n.  Pppd will send log mes-
              sages to at most one file or file descriptor (as well as sending
              the log messages to syslog), so  this  option  and  the  logfile
              option  are mutually exclusive.  The default is for pppd to send
              log messages to stdout (file descriptor 1),  unless  the  serial
              port is already open on stdout.

       logfile filename
              Append log messages to the file filename (as well as sending the
              log messages to syslog).  The file is opened with the privileges
              of the user who invoked pppd, in append mode.

       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).

       maxfail n
              Terminate  after  n  consecutive  failed connection attempts.  A
              value of 0 means no limit.  The default value is 10.

       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.

       mp     Enables the use of PPP multilink; this is an alias for the ‘mul-
              tilink’ option.  This option is currently only  available  under
              Linux.

       mppe-stateful
              Allow  MPPE  to  use  stateful  mode.   Stateless  mode is still
              attempted first.  The default is to disallow stateful mode.

       mpshortseq
              Enables the use of short (12-bit) sequence numbers in  multilink
              headers,  as opposed to 24-bit sequence numbers.  This option is
              only available under Linux, and only has any effect if multilink
              is enabled (see the multilink option).

       mrru n Sets  the  Maximum Reconstructed Receive Unit to n.  The MRRU is
              the maximum size for a received packet on  a  multilink  bundle,
              and  is  analogous  to  the  MRU for the individual links.  This
              option is currently only available under Linux, and only has any
              effect if multilink is enabled (see the multilink option).

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

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

       multilink
              Enables the use of the PPP multilink protocol.  If the peer also
              supports  multilink,  then this link can become part of a bundle
              between the local system and the peer.  If there is an  existing
              bundle  to  the  peer,  pppd will join this link to that bundle,
              otherwise pppd will create a new bundle.  See the MULTILINK sec-
              tion  below.   This  option  is  currently  only available under
              Linux.

       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.)

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

       noauth Do not require the peer to authenticate itself.  This option  is
              privileged.

       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 nor the cdtrcts nor the
              nocdtrcts option is given, the hardware flow control setting for
              the serial port is left unchanged.

       nocdtrcts
              This  option is a synonym for nocrtscts. Either of these options
              will disable both forms of hardware flow control.

       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.

       noendpoint
              Disables pppd from sending an endpoint discriminator to the peer
              or  accepting  one  from  the  peer  (see  the MULTILINK section
              below).  This option should only be  required  if  the  peer  is
              buggy.

       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.

       noipv6 Disable  IPv6CP  negotiation and IPv6 communication. This option
              should only be required if the peer is buggy and  gets  confused
              by requests from pppd for IPv6CP 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.

       noktune
              Opposite of the ktune option; disables pppd from changing system
              settings.

       nolog  Do  not  send  log  messages to a file or file descriptor.  This
              option cancels the logfd and logfile options.

       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.

       nomp   Disables the use of PPP multilink.   This  option  is  currently
              only available under Linux.

       nomppe Disables  MPPE  (Microsoft  Point to Point Encryption).  This is
              the default.

       nomppe-40
              Disable 40-bit encryption with MPPE.

       nomppe-128
              Disable 128-bit encryption with MPPE.

       nomppe-stateful
              Disable MPPE stateful mode.  This is the default.

       nompshortseq
              Disables the use of short (12-bit) sequence numbers in  the  PPP
              multilink  protocol, forcing the use of 24-bit sequence numbers.
              This option is currently only available under  Linux,  and  only
              has any effect if multilink is enabled.

       nomultilink
              Disables  the  use  of  PPP multilink.  This option is currently
              only available under Linux.

       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.

       notty  Normally, pppd requires a terminal device.   With  this  option,
              pppd will allocate itself a pseudo-tty master/slave pair and use
              the slave as its terminal device.  Pppd will create a child pro-
              cess  to  act  as  a  ‘character  shunt’  to transfer characters
              between the pseudo-tty master and its standard input and output.
              Thus  pppd  will  transmit characters on its standard output and
              receive characters on its standard input even if  they  are  not
              terminal  devices.   This  option  increases the latency and CPU
              overhead of transferring data over the ppp interface as  all  of
              the characters sent and received must flow through the character
              shunt process.  An explicit device name may not be given if this
              option is used.

       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  very basic firewall capability.  The filter-expression syntax
              is as described for tcpdump(1), except that qualifiers which are
              inappropriate  for  a  PPP  link, such as ether and arp, are not
              permitted.  Generally the filter expression should  be  enclosed
              in  single-quotes  to  prevent whitespace in the expression from
              being interpreted by the shell.  Note that  it  is  possible  to
              apply  different  constraints  to  incoming and outgoing packets
              using the inbound and outbound qualifiers. This option  is  cur-
              rently  only available under Linux, and requires that the kernel
              was configured to include PPP filtering support (CONFIG_PPP_FIL-
              TER).

       password password-string
              Specifies  the  password  to use for authenticating to the peer.
              Use of this option is discouraged, as the password is likely  to
              be  visible  to other users on the system (for example, by using
              ps(1)).

       persist
              Do not exit after a connection is  terminated;  instead  try  to
              reopen the connection. The maxfail option still has an effect on
              persistent connections.

       plugin filename
              Load the shared library object file filename as a plugin.   This
              is  a  privileged  option.  If filename does not contain a slash
              (/), pppd will look in the /usr/lib/pppd/version  directory  for
              the  plugin,  where  version  is the version number of pppd (for
              example, 2.4.2).

       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.

       privgroup group-name
              Allows  members  of  group group-name to use privileged options.
              This is a privileged option.  Use of this option  requires  care
              as  there  is no guarantee that members of group-name cannot use
              pppd to become  root  themselves.   Consider  it  equivalent  to
              putting the members of group-name in the kmem or disk group.

       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.

       pty script
              Specifies that the command script is to be used  to  communicate
              rather  than  a  specific  terminal  device.  Pppd will allocate
              itself a pseudo-tty master/slave pair and use the slave  as  its
              terminal device.  The script will be run in a child process with
              the pseudo-tty master as its  standard  input  and  output.   An
              explicit  device  name  may not be given if this option is used.
              (Note: if the record option is used in conjuction with  the  pty
              option,  the child process will have pipes on its standard input
              and output.)

       receive-all
              With this option, pppd will accept all control  characters  from
              the peer, including those marked in the receive asyncmap.  With-
              out this option, pppd will discard those characters as specified
              in  RFC1662.   This  option should only be needed if the peer is
              buggy.

       record filename
              Specifies that  pppd  should  record  all  characters  sent  and
              received  to  a  file  named  filename.   This file is opened in
              append mode, using the user’s  user-ID  and  permissions.   This
              option is implemented using a pseudo-tty and a process to trans-
              fer characters  between  the  pseudo-tty  and  the  real  serial
              device,  so  it  will  increase  the latency and CPU overhead of
              transferring data over the ppp interface.   The  characters  are
              stored  in  a  tagged  format with timestamps, which can be dis-
              played in readable form using the pppdump(8) program.

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

       remotenumber number
              Set  the  assumed  telephone  number  of  the  remote system for
              authentication purposes to number.

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

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

       refuse-mschap-v2
              With this option, pppd will not agree to authenticate itself  to
              the peer using MS-CHAPv2.

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

       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-mppe
              Require the use of MPPE (Microsoft Point to  Point  Encryption).
              This  option  disables all other compression types.  This option
              enables both 40-bit and 128-bit encryption.  In order  for  MPPE
              to successfully come up, you must have authenticated with either
              MS-CHAP or MS-CHAPv2.  This option is presently  only  supported
              under  Linux,  and  only  if  your kernel has been configured to
              include MPPE support.

       require-mppe-40
              Require the use of MPPE, with 40-bit encryption.

       require-mppe-128
              Require the use of MPPE, with 128-bit encryption.

       require-mschap
              Require the peer to authenticate itself using MS-CHAP  [Microsft
              Challenge Handshake Authentication Protocol] authentication.

       require-mschap-v2
              Require   the   peer  to  authenticate  itself  using  MS-CHAPv2
              [Microsft Challenge Handshake Authentication  Protocol,  Version
              2] authentication.

       require-eap
              Require  the  peer  to authenticate itself using EAP [Extensible
              Authentication Protocol] authentication.

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

       show-password
              When  logging  the  contents  of PAP packets, this option causes
              pppd to show the password string in the log message.

       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).

       srp-interval n
              If this parameter is given and pppd uses EAP SRP-SHA1 to authen-
              ticate  the  peer  (i.e., is the server), then pppd will use the
              optional lightweight SRP rechallenge mechanism at intervals of n
              seconds.   This option is faster than eap-interval reauthentica-
              tion because it uses a hash-based mechanism and does not  derive
              a new session key.

       srp-pn-secret string
              Set  the  long-term  pseudonym-generating secret for the server.
              This value is optional and if set, needs  to  be  known  at  the
              server  (authenticator)  side  only, and should be different for
              each server (or poll of identical servers).  It  is  used  along
              with  the  current date to generate a key to encrypt and decrypt
              the client’s identity contained in the pseudonym.

       srp-use-pseudonym
              When operating as an EAP SRP-SHA1 client,  attempt  to  use  the
              pseudonym  stored in ~/.ppp_psuedonym first as the identity, and
              save in this file any  pseudonym  offered  by  the  peer  during
              authentication.

       sync   Use  synchronous  HDLC  serial encoding instead of asynchronous.
              The device used by pppd with this option must have sync support.
              Currently  supports  Microgate SyncLink adapters under Linux and
              FreeBSD 2.2.8 and later.

       unit num
              Sets the ppp unit number (for a ppp0 or ppp1 etc interface name)
              for outbound connections.

       updetach
              With this option, pppd will detach from its controlling terminal
              once it has successfully established the ppp connection (to  the
              point  where  the first network control protocol, usually the IP
              control protocol, has come up).

       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).  This option is not  normally
              needed since the name option is privileged.

       usepeerdns
              Ask  the  peer  for up to 2 DNS server addresses.  The addresses
              supplied by the peer (if any) are passed to  the  /etc/ppp/ip-up
              script in the environment variables DNS1 and DNS2, and the envi-
              ronment variable USEPEERDNS will be set to 1.  In addition, pppd
              will  create  an /etc/ppp/resolv.conf file containing one or two
              nameserver lines with the address(es) supplied by the peer.

       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.  A value for this option from a privileged source
              cannot be overridden by a non-privileged user.

       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  whites-
       pace.   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.  This control is provided through  restrictions  on  which  IP
       addresses  the  peer  may  use, based on its authenticated identity (if
       any), and through restrictions on which options a  non-privileged  user
       may use.  Several of pppd’s options are privileged, in particular those
       which permit potentially insecure  configurations;  these  options  are
       only accepted in files which are under the control of the system admin-
       istrator, or if pppd is being run by root.

       The default behaviour of pppd is to allow an  unauthenticated  peer  to
       use a given IP address only if the system does not already have a route
       to that IP address.  For example, a system with a permanent  connection
       to  the wider internet will normally have a default route, and thus all
       peers will have to authenticate themselves in order to set up a connec-
       tion.   On such a system, the auth option is the default.  On the other
       hand, a system where the PPP link is the only connection to the  inter-
       net will not normally have a default route, so the peer will be able to
       use almost any IP address without authenticating itself.

       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.

       When opening the device, pppd uses either the invoking user’s  user  ID
       or  the root UID (that is, 0), depending on whether the device name was
       specified by the user or the system administrator.  If the device  name
       comes from a privileged source, that is, /etc/ppp/options or an options
       file read using the call option, pppd uses full  root  privileges  when
       opening  the  device.   Thus,  by  creating  an  appropriate file under
       /etc/ppp/peers, the system administrator can allow users to establish a
       ppp  connection via a device which they would not normally have permis-
       sion to access.  Otherwise pppd uses the invoking user’s real UID  when
       opening the device.


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 three authentication protocols: the  Password
       Authentication  Protocol (PAP), Challenge Handshake Authentication Pro-
       tocol  (CHAP),  and  Extensible  Authentication  Protocol  (EAP).   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.  EAP supports CHAP-style authentication, and also includes
       the SRP-SHA1 mechanism, which is resistant to dictionary-based  attacks
       and does not require a cleartext password on the server side.

       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, MS-CHAP,
       MS-CHAPv2, and EAP MD5-Challenge, and /etc/ppp/srp-secrets for EAP SRP-
       SHA1).   All secrets files have the same format.  The secrets files can
       contain secrets for pppd to use in authenticating itself to other  sys-
       tems, as well as secrets for pppd to use when authenticating other sys-
       tems 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  a  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.
       Note that case is significant in the client and server names and in the
       secret.

       If the secret starts with an ‘@’, what follows is  assumed  to  be  the
       name  of  a file from which to read the secret.  A "*" as the client or
       server name matches any name.  When selecting a secret, pppd takes  the
       best match, i.e.  the match with the fewest wildcards.

       Any  following words on the same line are taken to be a list of accept-
       able IP addresses for that client.  If there are only 3  words  on  the
       line,  or  if  the  first word is "-", then all IP addresses are disal-
       lowed.  To allow any address, use "*".  A word starting with "!"  indi-
       cates  that the specified address is not acceptable.  An address may be
       followed by "/" and a number n, to indicate a whole  subnet,  i.e.  all
       addresses which have the same value in the most significant n bits.  In
       this form, the address may be followed by a plus sign ("+") to indicate
       that  one  address from the subnet is authorized, based on the ppp net-
       work interface unit number in use.  In this case, the host part of  the
       address will be set to the unit number plus one.

       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.  (For EAP SRP-
       SHA1,  see  the  srp-entry(8)  utility  for generating proper validator
       entries to be used in the "secret" field.)

       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 or EAP authentication is being used, because the peer will have
       sent it in the challenge packet.  However, if PAP is being  used,  pppd
       will  have  to  determine the peer’s name from the options specified by
       the user.  The user can specify  the  peer’s  name  directly  with  the
       remotename  option.   Otherwise, if the remote IP address was specified
       by a name (rather than in numeric form), that name will be used as  the
       peer’s name.  Failing that, pppd will use the null string as the peer’s
       name.

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

       Furthermore, if the login option was specified, the username and  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.

       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.


MULTILINK

       Multilink PPP provides the capability to combine two or more PPP  links
       between  a  pair of machines into a single ‘bundle’, which appears as a
       single virtual PPP link which has the combined bandwidth of  the  indi-
       vidual  links.  Currently, multilink PPP is only supported under Linux.

       Pppd detects that the link it is controlling is connected to  the  same
       peer  as  another  link using the peer’s endpoint discriminator and the
       authenticated identity of the peer (if it authenticates  itself).   The
       endpoint discriminator is a block of data which is hopefully unique for
       each peer.  Several types of  data  can  be  used,  including  locally-
       assigned  strings  of  bytes,  IP  addresses,  MAC  addresses, randomly
       strings of bytes, or E-164 phone numbers.  The  endpoint  discriminator
       sent to the peer by pppd can be set using the endpoint option.

       In  circumstances the peer may send no endpoint discriminator or a non-
       unique value.  The optional bundle option adds an extra string which is
       added  to  the peer’s endpoint discriminator and authenticated identity
       when matching up links to be joined together in a bundle.   The  bundle
       option  can also be used to allow the establishment of multiple bundles
       between the local system and the peer.  Pppd uses  a  TDB  database  in
       /var/run/pppd.tdb to match up links.

       Assuming that multilink is enabled and the peer is willing to negotiate
       multilink, then when pppd is invoked to bring up the first link to  the
       peer,  it  will  detect that no other link is connected to the peer and
       create a new bundle, that is, another ppp network interface unit.  When
       another  pppd  is invoked to bring up another link to the peer, it will
       detect the existing bundle and join its link to it.  Currently, if  the
       first  pppd  terminates (for example, because of a hangup or a received
       signal) the bundle is destroyed.


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, /etc/ppp/chap-secrets, or /etc/ppp/srp-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" that is to be allowed
       to dial in to the machine called "server" and use the IP  address  joe-
       spc.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

       (See srp-entry(8) for a means to generate the server’s entry when  SRP-
       SHA1  is in use.)  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  overridden  by  recompiling pppd with the macro LOG_PPP
       defined as the desired facility.)  See the syslog(8) documentation  for
       details  of  where  the syslog daemon will write the messages.  On most
       systems, the syslog daemon uses the /etc/syslog.conf  file  to  specify
       the destination(s) for syslog messages.  You may need to edit that file
       to suit.

       The debug option causes the contents of all  control  packets  sent  or
       received  to be logged, that is, all LCP, PAP, CHAP, EAP, or IPCP pack-
       ets.  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.


EXIT STATUS

       The  exit  status  of  pppd  is  set  to indicate whether any error was
       detected, or the reason for the link being terminated.  The values used
       are:

       0      Pppd  has detached, or otherwise the connection was successfully
              established and terminated at the peer’s request.

       1      An immediately fatal error of some kind  occurred,  such  as  an
              essential system call failing, or running out of virtual memory.

       2      An error was detected in processing the options given,  such  as
              two mutually exclusive options being used.

       3      Pppd is not setuid-root and the invoking user is not root.

       4      The  kernel  does  not  support PPP, for example, the PPP kernel
              driver is not included or cannot be loaded.

       5      Pppd terminated because it was sent a SIGINT, SIGTERM or  SIGHUP
              signal.

       6      The serial port could not be locked.

       7      The serial port could not be opened.

       8      The connect script failed (returned a non-zero exit status).

       9      The  command  specified  as the argument to the pty option could
              not be run.

       10     The PPP negotiation failed, that is, it didn’t reach  the  point
              where at least one network protocol (e.g. IP) was running.

       11     The peer system failed (or refused) to authenticate itself.

       12     The  link was established successfully and terminated because it
              was idle.

       13     The link was established successfully and terminated because the
              connect time limit was reached.

       14     Callback  was  negotiated  and  an  incoming  call should arrive
              shortly.

       15     The link was terminated because the peer is  not  responding  to
              echo requests.

       16     The link was terminated by the modem hanging up.

       17     The PPP negotiation failed because serial loopback was detected.

       18     The init script failed (returned a non-zero exit status).

       19     We failed to authenticate ourselves to the peer.


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.

       ORIG_UID
              The real user-id of the user who invoked pppd.

       PPPLOGNAME
              The  username  of  the  real  user-id that invoked pppd. This is
              always set.

       For the ip-down and auth-down scripts, pppd  also  sets  the  following
       variables giving statistics for the connection:

       CONNECT_TIME
              The  number  of  seconds  from  when the PPP negotiation started
              until the connection was terminated.

       BYTES_SENT
              The number of bytes sent (at the level of the serial port)  dur-
              ing the connection.

       BYTES_RCVD
              The  number  of bytes received (at the level of the serial port)
              during the connection.

       LINKNAME
              The logical name of the link, set with the linkname option.

       DNS1   If the peer supplies DNS server addresses, this variable is  set
              to the first DNS server address supplied.

       DNS2   If  the peer supplies DNS server addresses, this variable is set
              to the second DNS server address supplied.

       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/ipv6-up
              Like /etc/ppp/ip-up, except that it is executed when the link is
              available for sending and receiving IPv6 packets. It is executed
              with the parameters

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

       /etc/ppp/ipv6-down
              Similar  to /etc/ppp/ip-down, but it is executed when IPv6 pack-
              ets can no longer be transmitted on the  link.  It  is  executed
              with the same parameters as the ipv6-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.

       /var/run/ppp-name.pid (BSD or Linux),
              /etc/ppp/ppp-name.pid  (others)  Process-ID for pppd process for
              logical link name (see the linkname option).

       /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/MS-CHAP/MS-CHAPv2
              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/srp-secrets
              Names, secrets, and IP addresses for EAP 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.

       ~/.ppp_pseudonym
              Saved client-side SRP-SHA1 pseudonym.  See the srp-use-pseudonym
              option for details.

       /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.


SEE ALSO

       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.

       RFC2284
              Blunk, L.; Vollbrecht, J., PPP Extensible Authentication  Proto-
              col (EAP).  March 1998.

       RFC2472
              Haskin, D.  IP Version 6 over PPP December 1998.

       RFC2945
              Wu, T., The SRP Authentication and Key Exchange System September
              2000.

       draft-ietf-pppext-eap-srp-03.txt
              Carlson, J.; et al., EAP SRP-SHA1 Authentication Protocol.  July
              2001.


NOTES

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

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

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

       SIGUSR1
              This signal toggles the state of the debug option.

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



AUTHORS

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



                                                                       PPPD(8)

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