explain about behaviour when opening the device

[ppp.git] / pppd / pppd.8

.\" manual page [] for pppd 2.3
.\" $Id: pppd.8,v 1.33 1999/03/03 00:52:08 paulus 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.
.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.  This
option is privileged if the \fInoauth\fR option is used.
.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 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 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.  This option is privileged if the
\fInoauth\fR option is used.
.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 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).
.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. 
.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 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, and then only
if both the kernel and pppd were compiled with PPP_FILTER defined.
.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 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 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 8 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 hide-password
When logging the contents of PAP packets, this option causes pppd to
exclude the password string from the log.
.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 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
\fIn\fR 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 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 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 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 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 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 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 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 \fInodtrcts\fR option is given, the hardware
flow control setting for the serial port is left unchanged.
.TP
.B nodtrcts
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 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 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 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 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 comprssion.
.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 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.
.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 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 remotename \fIname
Set the assumed name of the remote system for authentication purposes
to \fIname\fR.
.TP
.B refuse-chap
With this option, pppd will not agree to authenticate itself to the
peer using CHAP.
.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-pap
Require the peer to authenticate itself using PAP [Password
Authentication Protocol] authentication.
.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 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 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.  This option is privileged if the \fInoauth\fR option is
used.
.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 two authentication protocols: the Password
Authentication Protocol (PAP) and the Challenge Handshake
Authentication 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.
.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).
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.
.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.  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.  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
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.
.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 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 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 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:
.IP
joespc  server  "joe's secret"  joespc.my.net
.LP
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 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 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.
.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/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 /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 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/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.
.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.