Added documentation for the "unit" parameter.

[ppp.git] / pppd / pppd.8

.\" manual page [] for pppd 2.4
.\" $Id: pppd.8,v 1.68 2002/11/24 11:31:46 etbe Exp $
.\" SH section heading
.\" SS subsection heading
.\" LP paragraph
.\" IP indented paragraph
.\" TP hanging label
.TH PPPD 8
.SH NAME
pppd \- Point to Point Protocol daemon
.SH SYNOPSIS
.B pppd
[
.I tty_name
] [
.I speed
] [
.I options
]
.SH DESCRIPTION
.LP
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.
.LP
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).
.SH FREQUENTLY USED OPTIONS
.TP
.I <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.  A value for this
option from a privileged source cannot be overridden by a
non-privileged user.
.TP
.I <speed>
Set the baud rate to <speed> (a decimal number).  On systems such as
4.4BSD and NetBSD, any speed can be specified.  Other systems
(e.g. SunOS) allow only a limited set of speeds.
.TP
.B asyncmap \fI<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) represents the character 0x1f or ^_.
If multiple \fIasyncmap\fR options are given, the values are ORed
together.  If no \fIasyncmap\fR option is given, no async character
map will be negotiated for the receive direction; the peer should then
escape \fIall\fR control characters.  To escape transmitted
characters, use the \fIescape\fR option.
.TP
.B 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
\fInoauth\fR option is specified, pppd will only allow the peer to use
IP addresses to which the system does not already have a route.
.TP
.B call \fIname
Read options from the file /etc/ppp/peers/\fIname\fR.  This file may
contain privileged options, such as \fInoauth\fR, even if pppd
is not being run by root.  The \fIname\fR string may not begin with /
or include .. as a pathname component.  The format of the options file
is described below.
.TP
.B connect \fIscript
Use the executable or shell command specified by \fIscript\fR 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.  A value
for this option from a privileged source cannot be overridden by a
non-privileged user.
.TP
.B crtscts
Use hardware flow control (i.e. RTS/CTS) to control the flow of
data on the serial port.  If neither the \fIcrtscts\fR, the
\fInocrtscts\fR, the \fIcdtrcts\fR nor the \fInocdtrcts\fR 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 stop sending to the
computer. This mode retains the ability to use DTR as
a modem control line.
.TP
.B 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 \fInodefaultroute\fR option has been specified.
.TP
.B disconnect \fIscript
Run the executable or shell command specified by \fIscript\fR 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.  A value for this option from a privileged
source cannot be overridden by a non-privileged user.
.TP
.B escape \fIxx,yy,...
Specifies that certain characters should be escaped on transmission
(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 commas.  Note that
almost any character can be specified for the \fIescape\fR option,
unlike the \fIasyncmap\fR option which only allows control characters
to be specified.  The characters which may not be escaped are those
with hex values 0x20 - 0x3f or 0x5e.
.TP
.B file \fIname
Read options from file \fIname\fR (the format is described below).
The file must be readable by the user who has invoked pppd.
.TP
.B init \fIscript
Run the executable or shell command specified by \fIscript\fR to
initialize the serial line.  This script would typically 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.
.TP
.B lock
Specifies that pppd should create a UUCP-style lock file for the
serial device to ensure exclusive access to the device.
.TP
.B mru \fIn
Set the MRU [Maximum Receive Unit] value to \fIn\fR. Pppd
will ask the peer to send packets of no more than \fIn\fR 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)
.TP
.B mtu \fIn
Set the MTU [Maximum Transmit Unit] value to \fIn\fR.  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 \fIn\fR bytes through the PPP network interface.  (Note that for 
IPv6 MTU must be at least 1280)
.TP
.B 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 without this option.
.SH OPTIONS
.TP
.I <local_IP_address>\fB:\fI<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
\fInoipdefault\fR
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 \fIipcp-accept-local\fR and/or
\fIipcp-accept-remote\fR options are given, respectively.
.TP
.B ipv6 \fI<local_interface_identifier>\fR,\fI<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
\fIipv6cp-use-ipaddr\fR
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, \fIipv6cp-use-persistent\fR option can be
used to replace the \fIipv6 <local>,<remote>\fR option. Otherwise the 
identifier is randomized.
.TP
.B active-filter \fIfilter-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 conjunction with the
\fBidle\fR option if there are packets being sent or received
regularly over the link (for example, routing information packets)
which would otherwise prevent the link from ever appearing to be idle.
The \fIfilter-expression\fR syntax is as described for tcpdump(1),
except that qualifiers which are inappropriate for a PPP link, such as
\fBether\fR and \fBarp\fR, 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. This option
is currently only available under NetBSD or Linux, and then only
if both the kernel and pppd were compiled with PPP_FILTER defined.
.TP
.B allow-ip \fIaddress(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).
.TP
.B allow-number \fInumber
Allow peers to connect from the given telephone number.  A trailing
`*' character will match all numbers beginning with the leading part.
.TP
.B bsdcomp \fInr,nt
Request that the peer compress packets that it sends, using the
BSD-Compress scheme, with a maximum code size of \fInr\fR bits, and
agree to compress packets sent to the peer with a maximum code size of
\fInt\fR bits.  If \fInt\fR is not specified, it defaults to the value
given for \fInr\fR.  Values in the range 9 to 15 may be used for
\fInr\fR and \fInt\fR; larger values give better compression but
consume more kernel memory for compression dictionaries.
Alternatively, a value of 0 for \fInr\fR or \fInt\fR disables
compression in the corresponding direction.  Use \fInobsdcomp\fR or
\fIbsdcomp 0\fR to disable BSD-Compress compression entirely.
.TP
.B cdtrcts
Use a non-standard hardware flow control (i.e. DTR/CTS) to control
the flow of data on the serial port.  If neither the \fIcrtscts\fR,
the \fInocrtscts\fR, the \fIcdtrcts\fR nor the \fInocdtrcts\fR
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.
.TP
.B chap-interval \fIn
If this option is given, pppd will rechallenge the peer every \fIn\fR
seconds.
.TP
.B chap-max-challenge \fIn
Set the maximum number of CHAP challenge transmissions to \fIn\fR
(default 10).
.TP
.B chap-restart \fIn
Set the CHAP restart interval (retransmission timeout for challenges)
to \fIn\fR seconds (default 3).
.TP
.B connect-delay \fIn
Wait for up \fIn\fR 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 \fBconnect\fR
or \fBpty\fR option is used.
.TP
.B 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 \fIdaemon\fR and level
\fIdebug\fR.  This information can be directed to a file by setting up
/etc/syslog.conf appropriately (see syslog.conf(5)).
.TP
.B default-asyncmap
Disable asyncmap negotiation, forcing all control characters to be
escaped for both the transmit and the receive direction.
.TP
.B 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.
.TP
.B deflate \fInr,nt
Request that the peer compress packets that it sends, using the
Deflate scheme, with a maximum window size of \fI2**nr\fR bytes, and
agree to compress packets sent to the peer with a maximum window size
of \fI2**nt\fR bytes.  If \fInt\fR is not specified, it defaults to
the value given for \fInr\fR.  Values in the range 9 to 15 may be used
for \fInr\fR and \fInt\fR; larger values give better compression but
consume more kernel memory for compression dictionaries.
Alternatively, a value of 0 for \fInr\fR or \fInt\fR disables
compression in the corresponding direction.  Use \fInodeflate\fR or
\fIdeflate 0\fR to disable Deflate compression entirely.  (Note: pppd
requests Deflate compression in preference to BSD-Compress if the peer
can do either.)
.TP
.B demand
Initiate the link only on demand, i.e. when data traffic is present.
With this option, the remote IP address must be specified 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 available, 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 \fIdemand\fR option implies the \fIpersist\fR option.  If this
behaviour is not desired, use the \fInopersist\fR option after the
\fIdemand\fR option.  The \fIidle\fR and \fIholdoff\fR
options are also useful in conjuction with the \fIdemand\fR option.
.TP
.B domain \fId
Append the domain name \fId\fR to the local host name for authentication
purposes.  For example, if gethostname() returns the name porsche, but
the fully qualified domain name is porsche.Quotron.COM, you could
specify \fIdomain Quotron.COM\fR.  Pppd would then use the name
\fIporsche.Quotron.COM\fR 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.
.TP
.B dryrun
With the \fBdryrun\fR option, pppd will print out all the option
values 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.
.TP
.B dump
With the \fBdump\fR option, pppd will print out all the option values
which have been set.  This option is like the \fBdryrun\fR option
except that pppd proceeds as normal rather than exiting.
.TP
.B endpoint \fI<epdisc>
Sets the endpoint discriminator sent by the local machine to the peer
during multilink negotiation to \fI<epdisc>\fR.  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 \fBnull\fR or of the form \fItype\fR:\fIvalue\fR, where
type is a decimal number or one of the strings \fBlocal\fR, \fBIP\fR,
\fBMAC\fR, \fBmagic\fR, or \fBphone\fR.  The value is an IP address in
dotted-decimal notation for the \fBIP\fR 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.
.TP
.B eap-interval \fIn
If this option is given and pppd authenticates the peer with EAP
(i.e., is the server), pppd will restart EAP authentication every
\fIn\fR seconds.  For EAP SRP-SHA1, see also the \fBsrp-interval\fR
option, which enables lightweight rechallenge.
.TP
.B eap-max-rreq \fIn
Set the maximum number of EAP Requests to which pppd will respond (as
a client) without hearing EAP Success or Failure.  (Default is 20.)
.TP
.B eap-max-sreq \fIn
Set the maximum number of EAP Requests that pppd will issue (as a
server) while attempting authentication.  (Default is 10.)
.TP
.B eap-restart \fIn
Set the retransmit timeout for EAP Requests when acting as a server
(authenticator).  (Default is 3 seconds.)
.TP
.B eap-timeout \fIn
Set the maximum time to wait for the peer to send an EAP Request when
acting as a client (authenticatee).  (Default is 20 seconds.)
.TP
.B 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.
.TP
.B holdoff \fIn
Specifies how many seconds to wait before re-initiating the link after
it terminates.  This option only has any effect if the \fIpersist\fR
or \fIdemand\fR option is used.  The holdoff period is not applied if
the link was terminated because it was idle.
.TP
.B idle \fIn
Specifies that pppd should disconnect if the link is idle for \fIn\fR
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 \fIpersist\fR option without the \fIdemand\fR option.
If the \fBactive-filter\fR
option is given, data packets which are rejected by the specified
activity filter also count as the link being idle.
.TP
.B 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.
.TP
.B 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.
.TP
.B ipcp-max-configure \fIn
Set the maximum number of IPCP configure-request transmissions to
\fIn\fR (default 10).
.TP
.B ipcp-max-failure \fIn
Set the maximum number of IPCP configure-NAKs returned before starting
to send configure-Rejects instead to \fIn\fR (default 10).
.TP
.B ipcp-max-terminate \fIn
Set the maximum number of IPCP terminate-request transmissions to
\fIn\fR (default 3).
.TP
.B ipcp-restart \fIn
Set the IPCP restart interval (retransmission timeout) to \fIn\fR
seconds (default 3).
.TP
.B ipparam \fIstring
Provides an extra parameter to the ip-up and ip-down scripts.  If this
option is given, the \fIstring\fR supplied is given as the 6th
parameter to those scripts.
.TP
.B ipv6cp-max-configure \fIn
Set the maximum number of IPv6CP configure-request transmissions to
\fIn\fR (default 10).
.TP
.B ipv6cp-max-failure \fIn
Set the maximum number of IPv6CP configure-NAKs returned before starting
to send configure-Rejects instead to \fIn\fR (default 10).
.TP
.B ipv6cp-max-terminate \fIn
Set the maximum number of IPv6CP terminate-request transmissions to
\fIn\fR (default 3).
.TP
.B ipv6cp-restart \fIn
Set the IPv6CP restart interval (retransmission timeout) to \fIn\fR
seconds (default 3).
.TP
.B 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.
.TP
.B ipx-network \fIn
Set the IPX network number in the IPXCP configure request frame to
\fIn\fR, 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.
.TP
.B ipx-node \fIn\fB:\fIm
Set the IPX node numbers. The two node numbers are separated from each
other with a colon character. The first number \fIn\fR is the local
node number. The second number \fIm\fR 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.
.TP
.B ipx-router-name \fI<string>
Set the name of the router. This is a string and is sent to the peer
as information data.
.TP
.B ipx-routing \fIn
Set the routing protocol to be received by this option. More than one
instance of \fIipx-routing\fR may be specified. The '\fInone\fR'
option (0) may be specified as the only instance of ipx-routing. The
values may be \fI0\fR for \fINONE\fR, \fI2\fR for \fIRIP/SAP\fR, and
\fI4\fR for \fINLSP\fR.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B ipxcp-max-configure \fIn
Set the maximum number of IPXCP configure request frames which the
system will send to \fIn\fR. The default is 10.
.TP
.B ipxcp-max-failure \fIn
Set the maximum number of IPXCP NAK frames which the local system will
send before it rejects the options. The default value is 3.
.TP
.B ipxcp-max-terminate \fIn
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.
.TP
.B kdebug \fIn
Enable debugging code in the kernel-level PPP driver.  The argument
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 configuration file.
.TP
.B 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 \fIproxyarp\fR 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.
.TP
.B lcp-echo-failure \fIn
If this option is given, pppd will presume the peer to be dead
if \fIn\fR LCP echo-requests are sent without receiving a valid LCP
echo-reply.  If this happens, pppd will terminate the
connection.  Use of this option requires a non-zero value for the
\fIlcp-echo-interval\fR 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.
.TP
.B lcp-echo-interval \fIn
If this option is given, pppd will send an LCP echo-request frame to
the peer every \fIn\fR seconds.  Normally the peer should respond to
the echo-request by sending an echo-reply.  This option can be used
with the \fIlcp-echo-failure\fR option to detect that the peer is no
longer connected.
.TP
.B lcp-max-configure \fIn
Set the maximum number of LCP configure-request transmissions to
\fIn\fR (default 10).
.TP
.B lcp-max-failure \fIn
Set the maximum number of LCP configure-NAKs returned before starting
to send configure-Rejects instead to \fIn\fR (default 10).
.TP
.B lcp-max-terminate \fIn
Set the maximum number of LCP terminate-request transmissions to
\fIn\fR (default 3).
.TP
.B lcp-restart \fIn
Set the LCP restart interval (retransmission timeout) to \fIn\fR
seconds (default 3).
.TP
.B linkname \fIname\fR
Sets the logical name of the link to \fIname\fR.  Pppd will create a
file named \fBppp-\fIname\fB.pid\fR in /var/run (or /etc/ppp on some
systems) containing its process ID.  This can be useful in determining
which instance of pppd is responsible for the link to a given peer
system.  This is a privileged option.
.TP
.B 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.
.TP
.B logfd \fIn
Send log messages to file descriptor \fIn\fR.  Pppd will send log
messages to at most one file or file descriptor (as well as sending
the log messages to syslog), so this option and the \fBlogfile\fR
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.
.TP
.B logfile \fIfilename
Append log messages to the file \fIfilename\fR (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.
.TP
.B 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.
.TP
.B maxconnect \fIn
Terminate the connection when it has been available for network
traffic for \fIn\fR seconds (i.e. \fIn\fR seconds after the first
network control protocol comes up).
.TP
.B maxfail \fIn
Terminate after \fIn\fR consecutive failed connection attempts.  A
value of 0 means no limit.  The default value is 10.
.TP
.B 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 terminated and before executing
the connect script.  On Ultrix, this option implies hardware flow
control, as for the \fIcrtscts\fR option.
.TP
.B mp
Enables the use of PPP multilink; this is an alias for the `multilink'
option.  This option is currently only available under Linux.
.TP
.B mppe-stateful
Allow MPPE to use stateful mode.  Stateless mode is still attempted first.
The default is to disallow stateful mode.  
.TP
.B 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).
.TP
.B mrru \fIn
Sets the Maximum Reconstructed Receive Unit to \fIn\fR.  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).
.TP
.B ms-dns \fI<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 \fBdns-addr\fR.)
.TP
.B ms-wins \fI<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 primary WINS address; the second
instance (if given) specifies the secondary WINS address.
.TP
.B 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 section below.  This option is
currently only available under Linux.
.TP
.B name \fIname
Set the name of the local system for authentication purposes to
\fIname\fR.  This is a privileged option.  With this option, pppd will
use lines in the secrets files which have \fIname\fR as the second
field when looking for a secret to use in authenticating the peer.  In
addition, unless overridden with the \fIuser\fR option, \fIname\fR
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 \fIname\fR.)
.TP
.B netmask \fIn
Set the interface netmask to \fIn\fR, 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.  (Note: on some platforms, pppd
will always use 255.255.255.255 for the netmask, if that is the only
appropriate value for a point-to-point interface.)
.TP
.B noaccomp
Disable Address/Control compression in both directions (send and
receive).
.TP
.B noauth
Do not require the peer to authenticate itself.  This option is
privileged.
.TP
.B nobsdcomp
Disables BSD-Compress compression; \fBpppd\fR will not request or
agree to compress packets using the BSD-Compress scheme.
.TP
.B 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.
.TP
.B nocrtscts
Disable hardware flow control (i.e. RTS/CTS) on the serial port.
If neither the \fIcrtscts\fR nor the \fInocrtscts\fR nor the
\fIcdtrcts\fR nor the \fInocdtrcts\fR option is given, the hardware
flow control setting for the serial port is left unchanged.
.TP
.B nocdtrcts
This option is a synonym for \fInocrtscts\fR. Either of these options will
disable both forms of hardware flow control.
.TP
.B nodefaultroute
Disable the \fIdefaultroute\fR 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.
.TP
.B nodeflate
Disables Deflate compression; pppd will not request or agree to
compress packets using the Deflate scheme.
.TP
.B nodetach
Don't detach from the controlling terminal.  Without this option, if a
serial device other than the terminal on the standard input is
specified, pppd will fork to become a background process.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B noipdefault
Disables the default behaviour when no local IP address is specified,
which is to determine (if possible) the local IP address from the
hostname.  With this option, the peer will have to supply the local IP
address during IPCP negotiation (unless it specified explicitly on the
command line or in an options file).
.TP
.B 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.
.TP
.B noktune
Opposite of the \fIktune\fR option; disables pppd from changing system
settings.
.TP
.B nolog
Do not send log messages to a file or file descriptor.  This option
cancels the \fBlogfd\fR and \fBlogfile\fR options.
.TP
.B 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.
.TP
.B nomp
Disables the use of PPP multilink.  This option is currently only
available under Linux.
.TP
.B nomppe
Disables MPPE (Microsoft Point to Point Encryption).  This is the default.
.TP
.B nomppe-40
Disable 40\-bit encryption with MPPE.
.TP
.B nomppe-128
Disable 128\-bit encryption with MPPE.
.TP
.B nomppe-stateful
Disable MPPE stateful mode.  This is the default.
.TP
.B 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.
.TP
.B nomultilink
Disables the use of PPP multilink.  This option is currently only
available under Linux.
.TP
.B nopcomp
Disable protocol field compression negotiation in both the receive and
the transmit direction.
.TP
.B nopersist
Exit once a connection has been made and terminated.  This is the
default unless the \fIpersist\fR or \fIdemand\fR option has been
specified.
.TP
.B nopredictor1
Do not accept or agree to Predictor-1 compression.
.TP
.B noproxyarp
Disable the \fIproxyarp\fR 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.
.TP
.B 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 process 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.
.TP
.B novj
Disable Van Jacobson style TCP/IP header compression in both the
transmit and the receive direction.
.TP
.B 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.
.TP
.B 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.
.TP
.B pap-max-authreq \fIn
Set the maximum number of PAP authenticate-request transmissions to
\fIn\fR (default 10).
.TP
.B pap-restart \fIn
Set the PAP restart interval (retransmission timeout) to \fIn\fR
seconds (default 3).
.TP
.B pap-timeout \fIn
Set the maximum time that pppd will wait for the peer to authenticate
itself with PAP to \fIn\fR seconds (0 means no limit).
.TP
.B pass-filter \fIfilter-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 \fIfilter-expression\fR syntax is as described for tcpdump(1),
except that qualifiers which are inappropriate for a PPP link, such as
\fBether\fR and \fBarp\fR, 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 \fBinbound\fR and \fBoutbound\fR qualifiers. This
option is currently only available under NetBSD, and then only if both
the kernel and pppd were compiled with PPP_FILTER defined.
.TP
.B persist
Do not exit after a connection is terminated; instead try to reopen
the connection. The \fBmaxfail\fR option still has an effect on
persistent connections.
.TP
.B plugin \fIfilename
Load the shared library object file \fIfilename\fR as a plugin.  This
is a privileged option.  If \fIfilename\fR does not contain a slash
(/), pppd will look in the \fB/usr/lib/pppd/\fIversion\fR directory
for the plugin, where
\fIversion\fR is the version number of pppd (for example, 2.4.2).
.TP
.B predictor1
Request that the peer compress frames that it sends using Predictor-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.
.TP
.B privgroup \fIgroup-name
Allows members of group \fIgroup-name\fR to use privileged options.
This is a privileged option.  Use of this option requires care as
there is no guarantee that members of \fIgroup-name\fR cannot use pppd
to become root themselves.  Consider it equivalent to putting the
members of \fIgroup-name\fR in the kmem or disk group.
.TP
.B 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.
.TP
.B pty \fIscript
Specifies that the command \fIscript\fR 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 \fIscript\fR 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
\fIrecord\fR option is used in conjuction with the \fIpty\fR option,
the child process will have pipes on its standard input and output.)
.TP
.B receive-all
With this option, pppd will accept all control characters from the
peer, including those marked in the receive asyncmap.  Without this
option, pppd will discard those characters as specified in RFC1662.
This option should only be needed if the peer is buggy.
.TP
.B record \fIfilename
Specifies that pppd should record all characters sent and received to
a file named \fIfilename\fR.  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 transfer 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
displayed in readable form using the pppdump(8) program.
.TP
.B remotename \fIname
Set the assumed name of the remote system for authentication purposes
to \fIname\fR.
.TP
.B remotenumber \fInumber
Set the assumed telephone number of the remote system for authentication
purposes to \fInumber\fR.
.TP
.B refuse-chap
With this option, pppd will not agree to authenticate itself to the
peer using CHAP.
.TP
.B refuse-mschap
With this option, pppd will not agree to authenticate itself to the
peer using MS-CHAP.
.TP
.B refuse-mschap-v2
With this option, pppd will not agree to authenticate itself to the
peer using MS-CHAPv2.
.TP
.B refuse-eap
With this option, pppd will not agree to authenticate itself to the
peer using EAP.
.TP
.B refuse-pap
With this option, pppd will not agree to authenticate itself to the
peer using PAP.
.TP
.B require-chap
Require the peer to authenticate itself using CHAP [Challenge
Handshake Authentication Protocol] authentication.
.TP
.B 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.
.TP
.B require-mppe-40
Require the use of MPPE, with 40\-bit encryption.
.TP
.B require-mppe-128
Require the use of MPPE, with 128\-bit encryption.
.TP
.B require-mschap
Require the peer to authenticate itself using MS-CHAP [Microsft Challenge
Handshake Authentication Protocol] authentication.
.TP
.B require-mschap-v2
Require the peer to authenticate itself using MS-CHAPv2 [Microsft Challenge
Handshake Authentication Protocol, Version 2] authentication.
.TP
.B require-eap
Require the peer to authenticate itself using EAP [Extensible
Authentication Protocol] authentication.
.TP
.B require-pap
Require the peer to authenticate itself using PAP [Password
Authentication Protocol] authentication.
.TP
.B show-password
When logging the contents of PAP packets, this option causes pppd to
show the password string in the log message.
.TP
.B 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).
.TP
.B srp-interval \fIn
If this parameter is given and pppd uses EAP SRP-SHA1 to authenticate
the peer (i.e., is the server), then pppd will use the optional
lightweight SRP rechallenge mechanism at intervals of \fIn\fR
seconds.  This option is faster than \fBeap-interval\fR
reauthentication because it uses a hash-based mechanism and does not
derive a new session key.
.TP
.B srp-pn-secret \fIstring
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.
.TP
.B 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.
.TP
.B 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.
.TP
.B unit \fInum
Sets the ppp unit number (for a ppp0 or ppp1 etc interface name) for outbound
connections.
.TP
.B 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).
.TP
.B usehostname
Enforce the use of the hostname (with domain name appended, if given)
as the name of the local system for authentication purposes (overrides
the \fIname\fR option).  This option is not normally needed since the
\fIname\fR option is privileged.
.TP
.B 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.  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.
.TP
.B user \fIname
Sets the name used for authenticating the local system to the peer to
\fIname\fR.
.TP
.B vj-max-slots \fIn
Sets the number of connection slots to be used by the Van Jacobson
TCP/IP header compression and decompression code to \fIn\fR, which
must be between 2 and 16 (inclusive).
.TP
.B welcome \fIscript
Run the executable or shell command specified by \fIscript\fR 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.
.TP
.B xonxoff
Use software flow control (i.e. XON/XOFF) to control the flow of data on
the serial port.
.SH 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.\fIttyname\fR (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.\fIttyname\fR
file is read.)  In forming the name of the options.\fIttyname\fR file,
the initial /dev/ is removed from the terminal name, and any remaining
/ characters are replaced with dots.
.PP
An options file is parsed into a series of words, delimited by
whitespace.  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 \fIfile\fR or \fIcall\fR
options within an options file.
.SH SECURITY
.I 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
administrator, or if pppd is being run by root.
.PP
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 connection.  On such a system, the \fIauth\fR
option is the default.  On the other hand, a system where the
PPP link is the only connection to the internet will not normally have
a default route, so the peer will be able to use almost any IP address
without authenticating itself.
.PP
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 \fIfile\fR
option.  Privileged options may be used in /etc/ppp/options file or in
an options file read using the \fIcall\fR option.  If pppd is being
run by the root user, privileged options can be used without
restriction.
.PP
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 \fIcall\fR 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 permission to access.  Otherwise pppd uses the invoking user's
real UID when opening the device.
.SH 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
password) with the server, and authenticates itself by proving that it
knows that secret.  Very often, the names used for authentication
correspond to the internet hostnames of the peers, but this is not
essential.
.LP
At present, pppd supports three authentication protocols: the Password
Authentication Protocol (PAP), Challenge Handshake Authentication
Protocol (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.
.LP
The PPP protocol, being symmetrical, allows both peers to require the
other to authenticate itself.  In that case, two separate and
independent authentication exchanges will occur.  The two exchanges
could use different authentication protocols, and in principle,
different names could be used in the two exchanges.
.LP
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.
.LP
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
systems, as well as secrets for pppd to use when authenticating other
systems to itself.
.LP
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.
.LP
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.
.LP
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.
.LP
Any following words on the same line are taken to be a list of
acceptable 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
disallowed.  To allow any address, use "*".  A word starting with "!"
indicates that the specified address is \fInot\fR acceptable.  An
address may be followed by "/" and a number \fIn\fR, to indicate a
whole subnet, i.e. all addresses which have the same value in the most
significant \fIn\fR 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 network interface unit number in use.
In this case, the host part of the address will be set to the unit
number plus one.
.LP
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 \fIdomain\fR option is used.  This default can be
overridden with the \fIname\fR option, except when the
\fIusehostname\fR 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.)
.LP
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
\fIuser\fR 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 \fIremotename\fR 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.
.LP
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
\fIpapcrypt\fR option is given, the first (unencrypted) comparison is
omitted, for better security.
.LP
Furthermore, if the \fIlogin\fR option was specified, the username and
password 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 \fIlogin\fR option,
the secret in /etc/ppp/pap-secrets would be "", which will match any
password supplied by the peer.  This avoids the need to have the same
secret in two places.
.LP
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
terminated 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.
.LP
In some cases it is desirable to allow some hosts which can't
authenticate 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 password, it is possible to allow restricted access to
hosts which refuse to authenticate themselves.
.SH ROUTING
.LP
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.
Communication with other machines generally requires further
modification to routing tables and/or ARP (Address Resolution
Protocol) tables.  In most cases the \fIdefaultroute\fR and/or
\fIproxyarp\fR options are sufficient for this, but in some cases
further intervention is required.  The /etc/ppp/ip-up script can be
used for this.
.LP
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 \fIdefaultroute\fR option
causes pppd to create such a default route when IPCP comes up, and
delete it when the link is terminated.
.LP
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
communicate with the remote host.  The \fIproxyarp\fR 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.
.LP
When the \fIdemand\fR 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 negotiated addresses.  This may disrupt existing connections,
and the use of demand dialling with peers that do dynamic IP address
assignment is not recommended.
.SH 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
individual links.  Currently, multilink PPP is only supported under
Linux.
.LP
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.
.LP
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.
.LP
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.
.SH EXAMPLES
.LP
The following examples assume that the /etc/ppp/options file contains
the \fIauth\fR option (as in the default /etc/ppp/options file in the
ppp distribution).
.LP
Probably the most common use of pppd is to dial out to an ISP.  This
can be done with a command such as
.IP
pppd call isp
.LP
where the /etc/ppp/peers/isp file is set up by the system
administrator to contain something like this:
.IP
ttyS0 19200 crtscts
.br
connect '/usr/sbin/chat -v -f /etc/ppp/chat-isp'
.br
noauth
.LP
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
contains the script used by chat; it could for example contain
something like this:
.IP
ABORT "NO CARRIER"
.br
ABORT "NO DIALTONE"
.br
ABORT "ERROR"
.br
ABORT "NO ANSWER"
.br
ABORT "BUSY"
.br
ABORT "Username/Password Incorrect"
.br
"" "at"
.br
OK "at&d0&c1"
.br
OK "atdt2468135"
.br
"name:" "^Umyuserid"
.br
"word:" "\\qmypassword"
.br
"ispts" "\\q^Uppp"
.br
"~-^Uppp-~"
.LP
See the chat(8) man page for details of chat scripts.
.LP
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
.IP
pppd proxyarp
.LP
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 joespc.my.net, you would add an entry
like this to /etc/ppp/pap-secrets or /etc/ppp/chap-secrets:
.IP
joespc  server  "joe's secret"  joespc.my.net
.LP
(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.
.LP
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 \fIasyncmap a0000\fR.  If the path includes a telnet,
you probably should escape ^] as well (\fIasyncmap 200a0000\fR).  If
the path includes an rlogin, you will need to use the \fIescape ff\fR
option on the end which is running the rlogin client, since many
rlogin implementations are not transparent; they will remove the
sequence [0xff, 0xff, 0x73, 0x73, followed by any 8 bytes] from the
stream.
.SH DIAGNOSTICS
.LP
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.
.LP
The \fIdebug\fR option causes the contents of all control packets sent
or received to be logged, that is, all LCP, PAP, CHAP, EAP, 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 \fIdebug\fR option also
causes other debugging messages to be logged.
.LP
Debugging can also be enabled or disabled by sending a SIGUSR1 signal
to the pppd process.  This signal acts as a toggle.
.SH 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:
.TP
.B 0
Pppd has detached, or otherwise the connection was successfully
established and terminated at the peer's request.
.TP
.B 1
An immediately fatal error of some kind occurred, such as an essential
system call failing, or running out of virtual memory.
.TP
.B 2
An error was detected in processing the options given, such as two
mutually exclusive options being used.
.TP
.B 3
Pppd is not setuid-root and the invoking user is not root.
.TP
.B 4
The kernel does not support PPP, for example, the PPP kernel driver is
not included or cannot be loaded.
.TP
.B 5
Pppd terminated because it was sent a SIGINT, SIGTERM or SIGHUP
signal.
.TP
.B 6
The serial port could not be locked.
.TP
.B 7
The serial port could not be opened.
.TP
.B 8
The connect script failed (returned a non-zero exit status).
.TP
.B 9
The command specified as the argument to the \fIpty\fR option could
not be run.
.TP
.B 10
The PPP negotiation failed, that is, it didn't reach the point where
at least one network protocol (e.g. IP) was running.
.TP
.B 11
The peer system failed (or refused) to authenticate itself.
.TP
.B 12
The link was established successfully and terminated because it was
idle.
.TP
.B 13
The link was established successfully and terminated because the
connect time limit was reached.
.TP
.B 14
Callback was negotiated and an incoming call should arrive shortly.
.TP
.B 15
The link was terminated because the peer is not responding to echo
requests.
.TP
.B 16
The link was terminated by the modem hanging up.
.TP
.B 17
The PPP negotiation failed because serial loopback was detected.
.TP
.B 18
The init script failed (returned a non-zero exit status).
.TP
.B 19
We failed to authenticate ourselves to the peer.
.SH 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:
.TP
.B DEVICE
The name of the serial tty device being used.
.TP
.B IFNAME
The name of the network interface being used.
.TP
.B IPLOCAL
The IP address for the local end of the link.  This is only set when
IPCP has come up.
.TP
.B IPREMOTE
The IP address for the remote end of the link.  This is only set when
IPCP has come up.
.TP
.B PEERNAME
The authenticated name of the peer.  This is only set if the peer
authenticates itself.
.TP
.B SPEED
The baud rate of the tty device.
.TP
.B ORIG_UID
The real user-id of the user who invoked pppd.
.TP
.B PPPLOGNAME
The username of the real user-id that invoked pppd. This is always set.
.P
For the ip-down and auth-down scripts, pppd also sets the following
variables giving statistics for the connection:
.TP
.B CONNECT_TIME
The number of seconds from when the PPP negotiation started until the
connection was terminated.
.TP
.B BYTES_SENT
The number of bytes sent (at the level of the serial port) during the
connection.
.TP
.B BYTES_RCVD
The number of bytes received (at the level of the serial port) during
the connection.
.TP
.B LINKNAME
The logical name of the link, set with the \fIlinkname\fR option.
.P
Pppd invokes the following scripts, if they exist.  It is not an error
if they don't exist.
.TP
.B /etc/ppp/auth-up
A program or script which is executed after the remote system
successfully authenticates itself.  It is executed with the parameters
.IP
\fIinterface-name peer-name user-name tty-device speed\fR
.IP
Note that this script is not executed if the peer doesn't authenticate
itself, for example when the \fInoauth\fR option is used.
.TP
.B /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.
.TP
.B /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
.IP
\fIinterface-name tty-device speed local-IP-address
remote-IP-address ipparam\fR
.TP
.B /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.
.TP
.B /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
.IP
\fIinterface-name tty-device speed local-link-local-address
remote-link-local-address ipparam\fR
.TP
.B /etc/ppp/ipv6-down
Similar to /etc/ppp/ip-down, but it is executed when IPv6 packets can no
longer be transmitted on the link. It is executed with the same parameters 
as the ipv6-up script.
.TP
.B /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
.IP
\fIinterface-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\fR 
.IP
The local-IPX-routing-protocol and remote-IPX-routing-protocol field
may be one of the following:
.IP
NONE      to indicate that there is no routing protocol
.br
RIP       to indicate that RIP/SAP should be used
.br
NLSP      to indicate that Novell NLSP should be used
.br
RIP NLSP  to indicate that both RIP/SAP and NLSP should be used
.TP
.B /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.
.SH FILES
.TP
.B /var/run/ppp\fIn\fB.pid \fR(BSD or Linux), \fB/etc/ppp/ppp\fIn\fB.pid \fR(others)
Process-ID for pppd process on ppp interface unit \fIn\fR.
.TP
.B /var/run/ppp-\fIname\fB.pid \fR(BSD or Linux),
\fB/etc/ppp/ppp-\fIname\fB.pid \fR(others)
Process-ID for pppd process for logical link \fIname\fR (see the
\fIlinkname\fR option).
.TP
.B /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.
.TP
.B /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.
.TP
.B /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.
.TP
.B ~/.ppp_pseudonym
Saved client-side SRP-SHA1 pseudonym.  See the \fIsrp-use-pseudonym\fR
option for details.
.TP
.B /etc/ppp/options
System default options for pppd, read before user default options or
command-line options.
.TP
.B ~/.ppprc
User default options, read before /etc/ppp/options.\fIttyname\fR.
.TP
.B /etc/ppp/options.\fIttyname
System default options for the serial port being used, read after
~/.ppprc.  In forming the \fIttyname\fR 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.
.TP
.B /etc/ppp/peers
A directory containing options files which may contain privileged
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.
.SH SEE ALSO
.TP
.B RFC1144
Jacobson, V.
\fICompressing TCP/IP headers for low-speed serial links.\fR
February 1990.
.TP
.B RFC1321
Rivest, R.
.I The MD5 Message-Digest Algorithm.
April 1992.
.TP
.B RFC1332
McGregor, G.
.I PPP Internet Protocol Control Protocol (IPCP).
May 1992.
.TP
.B RFC1334
Lloyd, B.; Simpson, W.A.
.I PPP authentication protocols.
October 1992.
.TP
.B RFC1661
Simpson, W.A.
.I The Point\-to\-Point Protocol (PPP).
July 1994.
.TP
.B RFC1662
Simpson, W.A.
.I PPP in HDLC-like Framing.
July 1994.
.TP
.B RFC2284
Blunk, L.; Vollbrecht, J.,
.I PPP Extensible Authentication Protocol (EAP).
March 1998.
.TP
.B RFC2472
Haskin, D.
.I IP Version 6 over PPP
December 1998.
.TP
.B RFC2945
Wu, T.,
.I The SRP Authentication and Key Exchange System
September 2000.
.TP
.B draft-ietf-pppext-eap-srp-03.txt
Carlson, J.; et al.,
.I EAP SRP-SHA1 Authentication Protocol.
July 2001.
.SH NOTES
The following signals have the specified effect when sent to pppd.
.TP
.B SIGINT, SIGTERM
These signals cause pppd to terminate the link (by closing LCP),
restore the serial device settings, and exit.
.TP
.B SIGHUP
This signal causes pppd to terminate the link, restore the serial
device settings, and close the serial device.  If the \fIpersist\fR or
\fIdemand\fR 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.
.TP
.B SIGUSR1
This signal toggles the state of the \fIdebug\fR option.
.TP
.B 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.)

.SH 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.