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pppd - Point to Point Protocol daemon

 

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).
        <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).  (Note that for IPv6 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
               IPv6 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.
 
        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 con‐
               junction 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
               packets) are being sent or received.  Note: it is not  advisable
               to  use  this  option with the persist option without the demand
               option.  If the active-filter  option  is  given,  data  packets
               which  are  rejected by the specified activity filter also count
               as the link being idle.
 
        ipcp-accept-local
               With this option, pppd will accept the peer’s idea of our  local
               IP  address,  even  if  the local IP address was specified in an
               option.
 
        ipcp-accept-remote
               With this option, pppd  will  accept  the  peer’s  idea  of  its
               (remote) IP address, even if the remote IP address was specified
               in an option.
 
        ipcp-max-configure n
               Set the maximum number of IPCP  configure-request  transmissions
               to n (default 10).
 
        ipcp-max-failure n
               Set  the  maximum  number of IPCP configure-NAKs returned before
               starting to send configure-Rejects instead to n (default 10).
 
        ipcp-max-terminate n
               Set the maximum number of IPCP  terminate-request  transmissions
               to n (default 3).
 
        ipcp-restart n
               Set the IPCP restart interval (retransmission timeout) to n 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 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 number of IPXCP terminate request frames  before
               the  local  system  considers  that the peer is not listening to
               them.  The default value is 3.
 
        kdebug n
               Enable debugging code in the kernel-level PPP driver.  The 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.
 
        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.
 
        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
               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 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 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.  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/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.
 
        /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.
        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)
 

Sections

Based on BSD UNIX
FreeBSD is an advanced operating system for x86 compatible (including Pentium and Athlon), amd64 compatible (including Opteron, Athlon64, and EM64T), UltraSPARC, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.