NetBSD/usr.sbin/pppd/pppd.8

.\" manual page [] for pppd 2.0
.\" $Id: pppd.8,v 1.13 1996/05/22 01:41:51 mrg 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.
.B 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 controlling terminal is given,
.I pppd
will use the controlling 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.
.I 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 \fBasyncmap\fR options are
given, the values are ORed together.
If no \fBasyncmap\fR option is given, no async character map will be
negotiated for the receive direction; the peer should then escape
\fIall\fR control characters.
.TP
.B auth
Require the peer to authenticate itself before allowing network
packets to be sent or received.
.TP
.B connect \fI<p>
Use the executable or shell command specified by \fI<p>\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.
.TP
.B crtscts
Use hardware flow control (i.e. RTS/CTS) to control the flow of data
on the serial port.  If neither the \fBcrtscts\fR nor the
\fB\-crtscts\fR option is given, the hardware flow control setting for
the serial port is left unchanged.
.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.
.TP
.B disconnect \fI<p>
Run the executable or shell command specified by \fI<p>\fR after
\fIpppd\fR 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.
.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 \fBescape\fR option,
unlike the \fBasyncmap\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 \fI<f>
Read options from file <f> (the format is described below).
.TP
.B lock
Specifies that \fIpppd\fR should create a UUCP-style lock file for the
serial device to ensure exclusive access to the device.
.TP
.B mru \fI<n>
Set the MRU [Maximum Receive Unit] value to <n> for negotiation.
.I pppd
will ask the peer to send packets of no more than <n> bytes.  The
minimum MRU value is 128.  The default MRU value is 1500.  A value of
296 is recommended for slow links (40 bytes for TCP/IP header + 256
bytes of data).
.TP
.B mtu \fI<n>
Set the MTU [Maximum Transmit Unit] value to \fI<n>\fR.  Unless the
peer requests a smaller value via MRU negotiation, \fIpppd\fR will
request that the kernel networking code send data packets of no more
than \fIn\fR bytes through the PPP network interface. 
.TP
.B netmask \fI<n>
Set the interface netmask to <n>, a 32 bit netmask in "decimal dot"
notation (e.g. 255.255.255.0).  If this option is given, the value
specified is ORed with the default netmask.  The default netmask is
chosen based on the negotiated remote IP address; it is the
appropriate network mask for the class of the remote IP address, ORed
with the netmasks for any non point-to-point network interfaces in the
system which are on the same network.
.TP
.B passive
Enables the "passive" option in the LCP.  With this option,
.I pppd
will attempt to initiate a connection; if no reply is received from
the peer,
.I pppd
will then just wait passively for a valid LCP packet from the peer
(instead of exiting, as it does without this option).
.TP
.B silent
With this option,
.I 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 \fIpppd\fR).
.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
.B noipdefault
option is given).  The remote address will be obtained from the peer
if not specified in any option.  Thus, in simple cases, this option is
not required.  If a local and/or remote IP address is specified with
this option,
.I pppd
will not accept a different value from the peer in the IPCP
negotiation, unless the
.B ipcp-accept-local
and/or
.B ipcp-accept-remote
options are given, respectively.
.TP
.B -ac
Disable Address/Control compression negotiation (use default, i.e.
address/control field compression disabled).
.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.
.TP
.B -all
Don't request or allow negotiation of any options for LCP and IPCP (use
default values).
.TP
.B -am
Disable asyncmap negotiation (use the default asyncmap, i.e. escape
all control characters).
.TP
.B -as \fI<n>
Same as
.B asyncmap \fI<n>
.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.
.TP
.B \-bsdcomp
Disables BSD-Compress compression; \fBpppd\fR will not request or
agree to compress packets using the BSD-Compress scheme.
.TP
.B -ccp
Disable CCP (Compression Control Protocol) negotiation.  This option
should only be required if the peer is buggy and gets confused by
requests from
.I pppd
for CCP negotiation.
.TP
.B +chap
Require the peer to authenticate itself using CHAP [Challenge-Handshake
Authentication Protocol] authentication.
.TP
.B -chap
Don't agree to authenticate using CHAP.
.TP
.B chap-interval \fI<n>
If this option is given,
.I pppd
will rechallenge the peer every <n> seconds.
.TP
.B chap-max-challenge \fI<n>
Set the maximum number of CHAP challenge transmissions to <n> (default
10).
.TP
.B chap-restart \fI<n>
Set the CHAP restart interval (retransmission timeout for challenges)
to <n> seconds (default 3).
.TP
.B -crtscts
Disable hardware flow control (i.e. RTS/CTS) on the serial port.  If
neither the \fBcrtscts\fR nor the \fB\-crtscts\fR option is given,
the hardware flow control setting for the serial port is left
unchanged.
.TP
.B -d
Increase debugging level (same as the \fBdebug\fR option).
.TP
.B debug
Increase debugging level (same as \fB\-d\fR).
If this option is given, \fIpppd\fR 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 \-defaultroute
Disable the \fBdefaultroute\fR option.  The system administrator who
wishes to prevent users from creating default routes with \fIpppd\fR
can do so by placing this option in the /etc/ppp/options file.
.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 bits, and
agree to compress packets sent to the peer with a maximum window size of
\fI2**nt\fR bits.  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.  (Note: \fBpppd\fR
requests Deflate compression in preference to BSD-Compress
if the peer can do either.)
.TP
.B \-deflate
Disables Deflate compression; \fBpppd\fR will not request or agree to
compress packets using the Deflate scheme.
.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 specific by the user
on the command line or in an options file.  \fBpppd\fR will initially
configure the interface and enable it for IP traffic without
connecting to the peer.  When traffic is available, \fBpppd\fR will
connect to the peer and perform negotiation, authentication, etc.
When this is completed, \fBpppd\fR will commence passing data packets
(i.e., IP packets) across the link.  The persist, idle and holdoff
options are often useful in conjuction with this option.
.TP
.B -detach
Don't fork to become a background process (otherwise
.I pppd
will do so if a serial device other than its controlling terminal is
specified).
.TP
.B ms-dns \fI<addr>
If
.I pppd
is acting as a server for Microsoft Windows clients, this option
allows
.I 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.
.TP
.B domain \fI<d>
Append the domain name <d> 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 would use the
domain option to set the domain name to Quotron.COM.
.TP
.B holdoff \fI<n>
Specifies how many seconds to wait before re-initiating the link after
it terminates.  This option only has effect if the persist option is
used.
.TP
.B idle \fI<n>
Specifies that \fBpppd\fR should disconnect if it is idle for
\fI<n>\fR seconds.  The link is idle when no data packets (i.e. IP
packets) are being sent or received.  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 -ip
Disable IPCP negotiation and IP communication.  This option should
only be required if the peer is buggy and gets confused by requests
from
.I pppd
for IPCP negotiation.
.TP
.B ipcp-accept-local
With this option,
.I 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,
.I 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 \fI<n>
Set the maximum number of IPCP configure-request transmissions to <n>
(default 10).
.TP
.B ipcp-max-failure \fI<n>
Set the maximum number of IPCP configure-NAKs returned before starting
to send configure-Rejects instead to <n> (default 10).
.TP
.B ipcp-max-terminate \fI<n>
Set the maximum number of IPCP terminate-request transmissions to <n>
(default 3).
.TP
.B ipcp-restart \fI<n>
Set the IPCP restart interval (retransmission timeout) to <n> 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 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.
.TP
.B lcp-echo-failure \fI<n>
If this option is given, \fIpppd\fR 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, \fIpppd\fR 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
\fIpppd\fR 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 \fI<n>
If this option is given, \fIpppd\fR will send an LCP echo-request
frame to the peer every \fIn\fR seconds.  Under Linux, the
echo-request is sent when no packets have been received from the peer
for \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 \fI<n>
Set the maximum number of LCP configure-request transmissions to <n>
(default 10).
.TP
.B lcp-max-failure \fI<n>
Set the maximum number of LCP configure-NAKs returned before starting
to send configure-Rejects instead to <n> (default 10).
.TP
.B lcp-max-terminate \fI<n>
Set the maximum number of LCP terminate-request transmissions to <n>
(default 3).
.TP
.B lcp-restart \fI<n>
Set the LCP restart interval (retransmission timeout) to <n> seconds
(default 3).
.TP
.B local
Don't use the modem control lines.  With this option,
.B 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.
.TP
.B modem
Use the modem control lines.  This option is the default.  With this
option,
.B 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 \fBcrtscts\fR option.  
.TP
.B -mn
Disable magic number negotiation.  With this option,
.I pppd
cannot detect a looped-back line.
.TP
.B -mru
Disable MRU [Maximum Receive Unit] negotiation.  With this option,
\fIpppd\fR will use the default MRU value of 1500 bytes.
.TP
.B name \fI<n>
Set the name of the local system for authentication purposes to <n>.
.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 -p
Same as the
.B passive
option.
.TP
.B +pap
Require the peer to authenticate itself using PAP.
.TP
.B -pap
Don't agree to authenticate using PAP.
.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 \fI<n>
Set the maximum number of PAP authenticate-request transmissions to
<n> (default 10).
.TP
.B pap-restart \fI<n>
Set the PAP restart interval (retransmission timeout) to <n> seconds
(default 3).
.TP
.B pap-timeout \fI<n>
Set the maximum time that
.I pppd
will wait for the peer to authenticate itself with PAP to
<n> 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 provide protection against IP address spoofing
and other attacks.
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.
.TP
.B -pc
Disable protocol field compression negotiation (use default, i.e.
protocol field compression disabled).
.TP
.B persist
Do not exit after a connection is terminated; instead try to reopen
the connection.
.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.
.TP
.B \-proxyarp
Disable the \fBproxyarp\fR option.  The system administrator who
wishes to prevent users from creating proxy ARP entries with
\fIpppd\fR can do so by placing this option in the /etc/ppp/options
file.
.TP
.B remotename \fI<n>
Set the assumed name of the remote system for authentication purposes
to <n>.
.TP
.B +ua \fI<p>
Agree to authenticate using PAP [Password Authentication Protocol] if
requested by the peer, and
use the data in file <p> for the user and password to send to the
peer. The file contains the remote user name, followed by a newline,
followed by the remote password, followed by a newline.  This option
is obsolescent.
.TP
.B usehostname
Enforce the use of the hostname as the name of the local system for
authentication purposes (overrides the
.B name
option).
.TP
.B user \fI<u>
Set the user name to use for authenticating this machine with the peer
using PAP to <u>.
.TP
.B -vj
Disable negotiation of Van Jacobson style TCP/IP header compression (use
default, i.e. no compression).
.TP
.B -vjccomp
Disable the connection-ID compression option in Van Jacobson style
TCP/IP header compression.  With this option, \fIpppd\fR will not omit
the connection-ID byte from Van Jacobson compressed TCP/IP headers,
nor ask the peer to do so.
.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 xonxoff
Use software flow control (i.e. XON/XOFF) to control the flow of data on
the serial port.  This option is only implemented on Linux systems
at present.
.SH OPTIONS FILES
Options can be taken from files as well as the command line.  
.I pppd
reads options from the files /etc/ppp/options and ~/.ppprc before
looking at the command line.  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 quotes (").  A backslash (\\) quotes the
following character.  A hash (#) starts a comment, which continues
until the end of the line.
.SH AUTHENTICATION
.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.  In part this is provided by the /etc/ppp/options file, where the
administrator can place options to require authentication whenever
.I pppd
is run, and in part by the PAP and CHAP secrets files, where the
administrator can restrict the set of IP addresses which individual
users may use.
.LP
The default behaviour of
.I pppd
is to agree to authenticate if requested, and to not
require authentication from the peer.  However, 
.I pppd
will not agree to
authenticate itself with a particular protocol if it has no secrets
which could be used to do so.
.LP
Authentication is based on secrets, which are selected from secrets
files (/etc/ppp/pap-secrets for PAP, /etc/ppp/chap-secrets for CHAP).
Both secrets files have the same format, and both can store secrets
for several combinations of server (authenticating peer) and client
(peer being authenticated).  Note that
.I pppd
can be both a server
and client, and that different protocols can be used in the two
directions if desired.
.LP
A secrets file is parsed into words as for a options file.  A secret
is specified by a line containing at least 3 words, in the order
client name, server name, secret.  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, it is assumed that any IP address
is OK; to disallow all IP addresses, use "-".  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, \fIpppd\fR 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.  Which secret to use is chosen based on the names of the host
(the `local name') and its peer (the `remote name').  The local name
is set as follows:
.TP 3
if the \fBusehostname\fR option is given,
then the local name is the hostname of this machine
(with the domain appended, if given)
.TP 3
else if the \fBname\fR option is given,
then use the argument of the first \fBname\fR option seen
.TP 3
else if the local IP address is specified with a hostname,
then use that name
.TP 3
else use the hostname of this machine (with the domain appended, if given)
.LP
When authenticating ourselves using PAP, there is also a `username'
which is the local name by default, but can be set with the \fBuser\fR
option or the \fB+ua\fR option.
.LP
The remote name is set as follows:
.TP 3
if the \fBremotename\fR option is given,
then use the argument of the last \fBremotename\fR option seen
.TP 3
else if the remote IP address is specified with a hostname,
then use that host name
.TP 3
else the remote name is the null string "".
.LP
Secrets are selected from the PAP secrets file as follows:
.TP 2
*
For authenticating the peer, look for a secret with client ==
username specified in the PAP authenticate-request, and server ==
local name.
.TP 2
*
For authenticating ourselves to the peer, look for a secret with
client == our username, server == remote name.
.LP
When authenticating the peer with PAP, a secret of "" matches any
password supplied by the peer.  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 the \fBpapcrypt\fR option is given, the
first (unencrypted) comparison is omitted, for better security.
.LP
If the \fBlogin\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
\fBlogin\fR option, the secret in /etc/ppp/pap-secrets would be "", to
avoid the need to have the same secret in two places.
.LP
Secrets are selected from the CHAP secrets file as follows:
.TP 2
*
For authenticating the peer, look for a secret with client == name
specified in the CHAP-Response message, and server == local name.
.TP 2
*
For authenticating ourselves to the peer, look for a secret with
client == local name, and server == name specified in the
CHAP-Challenge message.
.LP
Authentication must be satisfactorily completed before IPCP (or any
other Network Control Protocol) can be started.  If authentication
fails, \fIpppd\fR 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, \fIpppd\fR 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,
.I 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 some cases this will be done
automatically through the actions of the \fIrouted\fR or \fIgated\fR
daemons, but in most cases some further intervention is required.
.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 \fBdefaultroute\fR option causes \fIpppd\fR 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 \fBproxyarp\fR option causes \fIpppd\fR
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, \fIpppd\fR creates a
permanent, published ARP entry with the IP address of the remote host
and the hardware address of the network interface found.
.SH EXAMPLES
.LP
In the simplest case, you can connect the serial ports of two machines
and issue a command like
.IP
pppd /dev/ttya 9600 passive
.LP
to each machine, assuming there is no \fIgetty\fR running on the
serial ports.  If one machine has a \fIgetty\fR running, you can use
\fIkermit\fR or \fItip\fR on the other machine to log in to the first
machine and issue a command like
.IP
pppd passive
.LP
Then exit from the communications program (making sure the connection
isn't dropped), and issue a command like
.IP
pppd /dev/ttya 9600
.LP
The process of logging in to the other machine and starting \fIpppd\fR
can be automated by using the \fBconnect\fR option to run \fIchat\fR,
for example:
.IP
pppd /dev/ttya 38400 connect 'chat "" "" "login:" "username"
"Password:" "password" "% " "exec pppd passive"'
.LP
(Note however that running chat like this will leave the password
visible in the parameter list of pppd and chat.)
.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 \fBasyncmap a0000\fR.  If the path includes a telnet,
you probably should escape ^] as well (\fBasyncmap 200a0000\fR).
If the path includes an rlogin, you will need to use the \fBescape
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 \fIpppd\fR 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 \fBdebug\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.
If debugging is enabled at compile time, the \fBdebug\fR option also
causes other debugging messages to be logged.
.LP
Debugging can also be enabled or disabled by sending a
SIGUSR1 to the
.I pppd
process.  This signal acts as a toggle.
.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 \fIpppd\fR process on ppp interface unit \fIn\fR.
.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\fR
.IP
and with its standard input,
output and error streams redirected to \fB/dev/null\fR.
.IP
This program or script is executed with the same real and effective
user-ID as \fIpppd\fR, that is, at least the effective user-ID and
possibly the real user-ID will be \fBroot\fR.  This is so that it can
be used to manipulate routes, run privileged daemons (e.g.
\fBsendmail\fR), etc.  Be careful that the contents of the
/etc/ppp/ip-up and /etc/ppp/ip-down scripts do not compromise your
system's security.
.IP
This program or script is executed without an environment, so you
must either specify a PATH or use full pathnames (e.g. \fI/sbin/route\fR,
as opposed to \fIroute\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 with the same parameters as the ip-up script, and the same
security considerations apply, since it is executed with the same
effective and real user-IDs as \fIpppd\fR.
.TP
.B /etc/ppp/pap-secrets
Usernames, passwords and IP addresses for PAP authentication.
.TP
.B /etc/ppp/chap-secrets
Names, secrets and IP addresses for CHAP authentication.
.TP
.B /etc/ppp/options
System default options for
.I pppd,
read before user default options or command-line options.
.TP
.B ~/.ppprc
User default options, read before command-line options.
.TP
.B /etc/ppp/options.\fIttyname
System default options for the serial port being used, read after
command-line options.  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.
.SH SEE ALSO
.TP
.B RFC1144
Jacobson, V.
.I Compressing TCP/IP headers for low-speed serial links.
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 the
.I pppd
process.
.TP
.B SIGINT, SIGTERM
These signals cause \fBpppd\fR to terminate the link (by closing LCP),
restore the serial device settings, and exit.
.TP
.B SIGHUP
This signal causes \fBpppd\fR to terminate the link, restore the
serial device settings, and close the serial device.  If the
\fBpersist\fR option has been specified, \fBpppd\fR will try to reopen
the serial device and start another connection.  Otherwise \fBpppd\fR
will exit.
.TP
.B SIGUSR2
This signal causes
.B 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.  With the BSD Compress scheme, fatal
decompression errors generally indicate a bug in one or other
implementation.

.SH AUTHORS
Paul Mackerras (paulus@cs.anu.edu.au), based on earlier work by
Drew Perkins,
Brad Clements,
Karl Fox,
Greg Christy,
and
Brad Parker.