mxge: Disable flow control by default.

[dragonfly.git] / usr.sbin / pppd / pppd.8

.Dd August 31, 2013
.Dt PPPD 8
.Os
.Sh NAME
.Nm pppd
.Nd Point-to-Point Protocol daemon
.Sh SYNOPSIS
.Nm
.Op Ar tty_name
.Op Ar speed
.Op Ar options
.Sh DESCRIPTION
The Point-to-Point Protocol (PPP) provides a method for transmitting
datagrams over serial point-to-point links.
PPP is composed of three parts: a method for encapsulating datagrams over
serial links, an extensible Link Control Protocol (LCP), and
a family of Network Control Protocols (NCP) for establishing
and configuring different network-layer protocols.
.Pp
The encapsulation scheme is provided by driver code in the kernel.
.Nm
provides the basic LCP, authentication support, and an NCP for
establishing and configuring the Internet Protocol (IP) (called the IP
Control Protocol, IPCP).
.Ss FREQUENTLY USED OPTIONS
.Bl -ohang -offset indent
.It Ar tty_name
Communicate over the named device.
The string
.Dq /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,
.Nm
will use that terminal, and will not fork to put itself in the
background.
This option is privileged if the
.Cm noauth
option is used.
.It Ar speed
Set the baud rate to
.Ar speed
(a decimal number).
On systems such as
.Bx 4.4
and
.Nx ,
any speed can be specified, providing that it is
supported by the serial device driver.
Other systems (e.g. SunOS, Linux) allow only a limited set of speeds.
.It Cm active-filter Ar filter-expression
Specifies a packet filter to be applied to data packets to determine
which packets are to be regarded as link activity, and therefore reset
the idle timer, or cause the link to be brought up in demand-dialling
mode.
This option is useful in conjunction with the
.Cm idle
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
.Ar filter-expression
syntax is as described for
.Xr tcpdump 1 ,
except that qualifiers which are inappropriate for a PPP link, such as
.Cm ether
and
.Cm arp ,
are not permitted.
Generally the filter
expression should be enclosed in single-quotes to prevent whitespace
in the expression from being interpreted by the shell.
This option is only available if both the kernel and
.Nm
were compiled with
.Dv PPP_FILTER
defined.
.It Cm asyncmap Ar map
Set the async character map to
.Ar map .
This map describes which control characters cannot be successfully
received over the serial line.
.Nm
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
.Cm asyncmap
options are given, the values are ORed together.
If no
.Cm asyncmap
option is given, no async character
map will be negotiated for the receive direction;
the peer should then escape all control characters.
To escape transmitted characters, use the
.Cm escape
option.
.It Cm auth
Require the peer to authenticate itself before allowing network
packets to be sent or received.
.It Cm call Ar name
Read options from the file
.Pa /etc/ppp/peers/ Ns Ar name .
This file may contain privileged options, such as
.Cm noauth ,
even if
.Nm
is not being run by root.
The
.Ar name
string may not begin with
.Dq /
or include
.Dq ..
as a pathname component.
The format of the options file is described below.
.It Cm connect Ar script
Use the executable or shell command specified by
.Ar script
to set up the serial line.
This script would typically use the
.Xr chat 8
program to dial the modem and start the remote ppp session.
This option is privileged if the
.Cm noauth
option is used.
.It Cm connect-max-attempts Ar number
Attempt dial-out connection to remote system no more than specified
.Ar number
of times.
The default is 1.
If the connection is not made,
.Nm
will exit.
Requires that
.Cm persist
has been specified.
.It Cm crtscts
Use hardware flow control (i.e. RTS/CTS) to control the flow of data
on the serial port.
If neither the
.Cm crtscts
nor the
.Cm nocrtscts
option is given, the hardware flow control setting
for the serial port is left unchanged.
.It Cm 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
.Cm nodefaultroute
option has been specified.
.It Cm disconnect Ar script
Run the executable or shell command specified by
.Ar script
after
.Nm
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
.Cm noauth
option is used.
.It Cm escape Ar xx,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
.Cm escape
option, unlike the
.Cm asyncmap
option which only allows control characters to be specified.
The characters which may not be escaped are those
with hex values 0x20 to 0x3f or 0x5e.
.It Cm file Ar name
Read options from file
.Ar name
(the format is described below).
The file must be readable by the user who has invoked
.Nm .
.It Cm lock
Specifies that
.Nm
should create a UUCP-style lock file for the
serial device to ensure exclusive access to the device.
.It Cm mru Ar size
Set the Maximum Receive Unit (MRU) value to
.Ar size .
.Nm
will ask the peer to send packets of no more than
.Ar size
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).
.It Cm mtu Ar size
Set the Maximum Transmit Unit (MTU) value to
.Ar size .
Unless the peer requests a smaller value via MRU negotiation,
.Nm
will request that the kernel networking code send data packets of no more
than
.Ar size
bytes through the PPP network interface.
.It Cm passive
Enables the
.Dq passive
option in the LCP.
With this option,
.Nm
will attempt to initiate a connection;
if no reply is received from the peer,
.Nm
will then just wait passively for a valid LCP packet from
the peer, instead of exiting, as it would without this option.
.El
.Ss OPTIONS
.Bl -ohang -offset indent
.It Ar local_IP_address Ns Li : Ns Ar 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
.Cm 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,
.Nm
will not accept a different value from the peer in the IPCP
negotiation, unless the
.Cm ipcp-accept-local
and/or
.Cm ipcp-accept-remote
options are given, respectively.
.It Cm bsdcomp Ar nr Ns Li , Ns Ar nt
Request that the peer compress packets that it sends, using the
BSD-Compress scheme, with a maximum code size of
.Ar nr
bits, and
agree to compress packets sent to the peer with a maximum code size of
.Ar nt
bits.
If
.Ar nt
is not specified, it defaults to the value given for
.Ar nr .
Values in the range 9 to 15 may be used for
.Ar nr
and
.Ar nt ;
larger values give better compression but
consume more kernel memory for compression dictionaries.
Alternatively, a value of 0 for
.Ar nr
or
.Ar nt
disables compression in the corresponding direction.
Use
.Cm nobsdcomp
or
.Cm bsdcomp Li 0
to disable BSD-Compress compression entirely.
.It Cm chap-interval Ar number
If this option is given,
.Nm
will rechallenge the peer every
.Ar number
seconds.
.It Cm chap-max-challenge Ar number
Set the maximum number of CHAP challenge transmissions to
.Ar number .
The default is 10.
.It Cm chap-restart Ar number
Set the CHAP restart interval (retransmission timeout for challenges)
to
.Ar number
seconds.
The default is 3.
.It Cm debug
Enables connection debugging facilities.
If this option is given,
.Nm
will log the contents of all
control packets sent or received in a readable form.
The packets are logged through syslog with facility
.Sy daemon
and level
.Sy debug .
This information can be directed to a file by setting up
.Pa /etc/syslog.conf
appropriately (see
.Xr syslog.conf 5 ) .
.It Cm default-asyncmap
Disable asyncmap negotiation, forcing all control characters to be
escaped for both the transmit and the receive direction.
.It Cm default-mru
Disable Maximum Receive Unit (MRU) negotiation.
With this option,
.Nm
will use the default MRU value of 1500 bytes for both the
transmit and receive direction.
.It Cm deflate Ar nr Ns Li , Ns Ar nt
Request that the peer compress packets that it sends, using the
Deflate scheme, with a maximum window size of
.Li 2** Ns Ar nr
bytes, and agree to compress packets sent to the peer with a
maximum window size of
.Li 2** Ns Ar nt
bytes.
If
.Ar nt
is not specified, it defaults to the value given for
.Ar nr .
Values in the range 8 to 15 may be used for
.Ar nr
and
.Ar nt ;
larger values give better compression but
consume more kernel memory for compression dictionaries.
Alternatively, a value of 0 for
.Ar nr
or
.Ar nt
disables compression in the corresponding direction.
Use
.Cm nodeflate
or
.Cm deflate Li 0
to disable Deflate compression entirely.
Note:
.Nm
requests Deflate compression in preference to BSD-Compress if the peer
can do either.
.It Cm 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.
.Nm
will initially
configure the interface and enable it for IP traffic without
connecting to the peer.
When traffic is available,
.Nm
will connect to the peer and perform negotiation, authentication, etc.
When this is completed,
.Nm
will commence passing data packets
(i.e. IP packets) across the link.
The
.Cm demand
option implies the
.Cm persist
option.
If this behaviour is not desired, use the
.Cm nopersist
option after the
.Cm demand
option.
The
.Cm idle
and
.Cm holdoff
options are also useful in conjunction with the
.Cm demand
option.
.It Cm domain Ar name
Append the domain name
.Ar name
to the local host name for authentication purposes.
For example, if gethostname() returns the name
.Sq porsche ,
but the fully qualified domain name is
.Sq porsche.quotron.com ,
you could specify
.Cm domain Li quotron.com .
.Nm
would then use the name
.Sq porsche.quotron.com
for looking up secrets in the secrets file, and as the default name
to send to the peer when authenticating itself to the peer.
This option is privileged.
.It Cm holdoff Ar number
Specifies how many seconds to wait before re-initiating the link after
it terminates.
This option only has any effect if the
.Cm persist
or
.Cm demand
option is used.
The holdoff period is not applied if
the link was terminated because it was idle.
.It Cm idle Ar number
Specifies that
.Nm
should disconnect if the link is idle for
.Ar number
seconds.
The link is idle when no data packets (i.e. IP packets) are
being sent or received.
If the
.Cm active-filter
option is given, data packets which are rejected by the specified
activity filter also count as the link being idle.
Note: it is not advisable to use this option with the
.Cm persist
option without the
.Cm demand
option.
.It Cm ipcp-accept-local
With this option,
.Nm
will accept the peer's idea of our local IP
address, even if the local IP address was specified in an option.
.It Cm ipcp-accept-remote
With this option,
.Nm
will accept the peer's idea of its (remote) IP
address, even if the remote IP address was specified in an option.
.It Cm ipcp-max-configure Ar number
Set the maximum number of IPCP configure-request transmissions to
.Ar number .
The default is 10.
.It Cm ipcp-max-failure Ar number
Set the maximum number of IPCP configure-NAKs returned before starting
to send configure-Rejects instead to
.Ar number .
The default is 10.
.It Cm ipcp-max-terminate Ar number
Set the maximum number of IPCP terminate-request transmissions to
.Ar number .
The default is 3.
.It Cm ipcp-restart Ar number
Set the IPCP restart interval (retransmission timeout) to
.Ar number
seconds.
The default is 3.
.It Cm ipparam Ar string
Provides an extra parameter to the ip-up and ip-down scripts.
If this option is given, the
.Ar string
supplied is given as the 6th
parameter to those scripts.
.It Cm 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.
.It Cm ipx-network Ar number
Set the IPX network number in the IPXCP configure request frame to
.Ar number ,
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.
.It Cm ipx-node Ar local Ns Li : Ns Ar remote
Set the IPX node numbers.
The two node numbers are separated from each
other with a colon character.
The first number
.Ar local
is the local node number.
The second number
.Ar remote
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.
.It Cm ipx-router-name Ar string
Set the name of the router.
This is a string and is sent to the peer
as information data.
.It Cm ipx-routing Ar protocol
Set the routing protocol to be received by this option.
More than one instance of
.Cm ipx-routing
may be specified.
The values may be 0 for NONE, 2 for IRIP/SAP, and 4 for NLSP.
The NONE option may be specified as the only instance of ipx-routing.
.It Cm 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.
.It Cm 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.
.It Cm 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.
.It Cm ipxcp-max-configure Ar number
Set the maximum number of IPXCP configure request frames which the
system will send.
The default is 10.
.It Cm ipxcp-max-failure Ar number
Set the maximum number of IPXCP NAK frames which the local system will
send before it rejects the options.
The default is 3.
.It Cm ipxcp-max-terminate Ar number
Set the maximum number of IPXCP terminate request frames before the
local system considers that the peer is not listening to them.
The default is 3.
.It Cm kdebug Ar level
Enable debugging code in the kernel-level PPP driver.
The argument
.Ar level
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
.Xr syslogd 8 ,
to a file as directed in the
.Pa /etc/syslog.conf
configuration file.
.It Cm lcp-echo-failure Ar number
If this option is given,
.Nm
will presume the peer to be dead if
.Ar number
LCP echo-requests are sent without receiving a valid LCP echo-reply.
If this happens,
.Nm
will terminate the connection.
Use of this option requires a non-zero value for the
.Cm lcp-echo-interval
parameter.
This option can be used to enable
.Nm
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.
.It Cm lcp-echo-interval Ar number
If this option is given,
.Nm
will send an LCP echo-request frame to the peer every
.Ar number
seconds.
Normally the peer should respond to
the echo-request by sending an echo-reply.
This option can be used
with the
.Cm lcp-echo-failure
option to detect that the peer is no longer connected.
.It Cm lcp-max-configure Ar number
Set the maximum number of LCP configure-request transmissions to
.Ar number .
The default is 10.
.It Cm lcp-max-failure Ar number
Set the maximum number of LCP configure-NAKs returned before starting
to send configure-Rejects instead to
.Ar number .
The default is 10.
.It Cm lcp-max-terminate Ar number
Set the maximum number of LCP terminate-request transmissions to
.Ar number .
The default is 3.
.It Cm lcp-restart Ar number
Set the LCP restart interval (retransmission timeout) to
.Ar number
seconds.
The default is 3.
.It Cm local
Don't use the modem control lines.
With this option,
.Nm
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.
.It Cm 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
.Pa /etc/ppp/pap-secrets
file as well as the system password database to be allowed access.
.It Cm maxconnect Ar number
Terminate the connection when it has been available for network
traffic for
.Ar number
seconds (i.e.\&
.Ar number
seconds after the first network control protocol comes up).
.It Cm modem
Use the modem control lines.
This option is the default.
With this option,
.Nm
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
.Cm crtscts
option.
.It Cm ms-dns Ar address
If
.Nm
is acting as a server for Microsoft Windows clients, this
option allows
.Nm
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.
Note: this option was present in some older versions of
.Nm
under the name
.Cm dns-addr .
.It Cm ms-wins Ar address
If
.Nm
is acting as a server for Microsoft Windows or Samba
clients, this option allows
.Nm
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.
.It Cm name Ar name
Set the name of the local system for authentication purposes to
.Ar name .
This is a privileged option.
With this option,
.Nm
will use lines in the secrets files which have
.Ar name
as the second
field when looking for a secret to use in authenticating the peer.
In addition, unless overridden with the
.Cm user
option,
.Cm name
will be used as the name to send to the peer when authenticating the
local system to the peer.
Note:
.Nm
does not append the domain name to
.Ar name .
.It Cm netmask Ar mask
Set the interface netmask to
.Ar mask ,
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.
.It Cm noaccomp
Disable Address/Control compression in both directions (send and
receive).
.It Cm noauth
Do not require the peer to authenticate itself.
This option is privileged if the
.Cm auth
option is specified in
.Pa /etc/ppp/options .
.It Cm nobsdcomp
Disables BSD-Compress compression;
.Nm
will not request or
agree to compress packets using the BSD-Compress scheme.
.It Cm noccp
Disable Compression Control Protocol (CCP) negotiation.
This option
should only be required if the peer is buggy and gets confused by
requests from
.Nm
for CCP negotiation.
.It Cm nocrtscts
Disable hardware flow control (i.e. RTS/CTS) on the serial port.
If neither the
.Cm crtscts
nor the
.Cm nocrtscts
option is given, the hardware flow control setting for the serial
port is left unchanged.
.It Cm nodefaultroute
Disable the
.Cm defaultroute
option.
The system administrator who
wishes to prevent users from creating default routes with
.Nm
can do so by placing this option in the
.Pa /etc/ppp/options
file.
.It Cm nodeflate
Disables Deflate compression;
.Nm
will not request or agree to compress packets using the Deflate scheme.
.It Cm 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,
.Nm
will fork to become a background process.
.It Cm noip
Disable IPCP negotiation and IP communication.
This option should only be required if the peer is buggy and gets
confused by requests from
.Nm
for IPCP negotiation.
.It Cm 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).
.It Cm noipx
Disable the IPXCP and IPX protocols.
This option should only be
required if the peer is buggy and gets confused by requests from
.Nm
for IPXCP negotiation.
.It Cm nomagic
Disable magic number negotiation.
With this option,
.Nm
cannot detect a looped-back line.
This option should only be needed if the peer is buggy.
.It Cm nopcomp
Disable protocol field compression negotiation in both the receive and
the transmit direction.
.It Cm nopersist
Exit once a connection has been made and terminated.
This is the default unless the
.Cm persist
or
.Cm demand
option has been specified.
.It Cm nopredictor1
Do not accept or agree to Predictor-1 compression.
.It Cm noproxyarp
Disable the
.Cm proxyarp
option.
The system administrator who
wishes to prevent users from creating proxy ARP entries with
.Nm
can do so by placing this option in the
.Pa /etc/ppp/options
file.
.It Cm novj
Disable Van Jacobson style TCP/IP header compression in both the
transmit and the receive direction.
.It Cm novjccomp
Disable the connection-ID compression option in Van Jacobson style
TCP/IP header compression.
With this option,
.Nm
will not omit the connection-ID byte from Van Jacobson compressed
TCP/IP headers, nor ask the peer to do so.
.It Cm papcrypt
Indicates that all secrets in the
.Pa /etc/ppp/pap-secrets
file which are
used for checking the identity of the peer are encrypted, and thus
.Nm
should not accept a password which, before encryption, is
identical to the secret from the
.Pa /etc/ppp/pap-secrets
file.
.It Cm pap-max-authreq Ar number
Set the maximum number of PAP authenticate-request transmissions to
.Ar number .
The default is 10.
.It Cm pap-restart Ar number
Set the PAP restart interval (retransmission timeout) to
.Ar number
seconds.
The default is 3.
.It Cm pap-timeout Ar number
Set the maximum time that
.Nm
will wait for the peer to authenticate itself with PAP to
.Ar number
seconds (0 means no limit).
.It Cm pass-filter Ar filter-expression
Specifies a packet filter to applied to data packets being sent or
received to determine which packets should be allowed to pass.
Packets which are rejected by the filter are silently discarded.
This
option can be used to prevent specific network daemons (such as
routed) using up link bandwidth, or to provide a basic firewall
capability.
The
.Ar filter-expression
syntax is as described for
.Xr tcpdump 1 ,
except that qualifiers which are inappropriate for a PPP link, such as
.Cm ether
and
.Cm arp , are not permitted.
Generally the filter
expression should be enclosed in single-quotes to prevent whitespace
in the expression from being interpreted by the shell.
Note that it
is possible to apply different constraints to incoming and outgoing
packets using the
.Cm inbound
and
.Cm outbound
qualifiers.
This option is currently only available under
.Nx ,
and then only if both the kernel and
.Nm
were compiled with
.Dv PPP_FILTER
defined.
.It Cm persist
Do not exit after a connection is terminated; instead try to reopen
the connection.
.It Cm 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.
.It Cm proxyarp
Add an entry to this system's Address Resolution Protocol (ARP) 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.
.It Cm remotename Ar name
Set the assumed name of the remote system for authentication purposes
to
.Ar name .
.It Cm refuse-chap
With this option,
.Nm
will not agree to authenticate itself to the peer using CHAP.
.It Cm refuse-pap
With this option,
.Nm
will not agree to authenticate itself to the peer using PAP.
.It Cm require-chap
Require the peer to authenticate itself using Challenge
Handshake Authentication Protocol (CHAP) authentication.
.It Cm require-pap
Require the peer to authenticate itself using Password
Authentication Protocol (PAP) authentication.
.It Cm silent
With this option,
.Nm
will not transmit LCP packets to initiate a connection until
a valid LCP packet is received from the peer (as for the
.Sq passive
option with ancient versions of
.Nm ) .
.It Cm 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
.Cm name
option).
.It Cm user Ar name
Sets the name used for authenticating the local system to the peer to
.Ar name .
.It Cm vj-max-slots Ar number
Sets the number of connection slots to be used by the Van Jacobson
TCP/IP header compression and decompression code to
.Ar number ,
which must be between 2 and 16 inclusively.
.It Cm welcome Ar script
Run the executable or shell command specified by
.Ar script
before initiating PPP negotiation, after the connect script
(if any) has completed.
This option is privileged if the
.Cm noauth
option is used.
.It Cm xonxoff
Use software flow control (i.e. XON/XOFF) to control the flow of data on
the serial port.
.El
.Ss SIGNALS
The following signals have the specified effect when sent to
.Nm :
.Bl -tag -width ".Dv SIGINT Ns , Dv SIGTERM" -offset indent
.It Dv SIGINT Ns , Dv SIGTERM
These signals cause
.Nm
to terminate the link (by closing LCP),
restore the serial device settings, and exit.
.It Dv SIGHUP
This signal causes
.Nm
to terminate the link, restore the serial
device settings, and close the serial device.
If the
.Cm persist
or
.Cm demand
option has been specified,
.Nm
will try to reopen the
serial device and start another connection (after the holdoff period).
Otherwise
.Nm
will exit.
If this signal is received during the holdoff period, it causes
.Nm
to end the holdoff period immediately.
.It Dv SIGUSR1
This signal toggles the state of the
.Cm debug
option.
.It Dv SIGUSR2
This signal causes
.Nm
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.)
.El
.Ss SECURITY
.Nm
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
.Pa /etc/ppp/options
file, where the administrator can place options to restrict the ways in which
.Nm
can be used, and in part by the PAP and CHAP secrets files, where the
administrator can restrict the set of IP addresses which individual
users may use.
.Pp
The normal way that
.Nm
should be set up is to have the
.Cm auth
option in the
.Pa /etc/ppp/options
file.
(This may become the default in later releases.)
If users wish to use
.Nm
to dial out to a peer which will refuse to authenticate itself
(such as an internet service provider), the system administrator
should create an options file under
.Pa /etc/ppp/peers
containing the
.Cm noauth
option, the name of the serial port to use, and the
.Cm connect
option (if required), plus any other appropriate options.
In this way,
.Nm
can be set up
to allow non-privileged users to make unauthenticated connections only
to trusted peers.
.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
.Nm ,
either on the command line, in the user's
.Pa ~/.ppprc
file, or in an options file read using the
.Cm file
option.
Privileged options may be used in
.Pa /etc/ppp/options
file or in an options file read using the
.Cm call
option.
If
.Nm
is being run by the root user, privileged options can be used without
restriction.
.Ss 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
.Sy client
and the other the
.Sy 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.
.Pp
At present,
.Nm
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.
.Pp
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.
.Pp
The default behaviour of
.Nm
is to agree to authenticate if
requested, and to not require authentication from the peer.
However,
.Nm
will not agree to authenticate itself with a particular protocol
if it has no secrets which could be used to do so.
.Pp
.Nm
stores secrets for use in authentication in secrets
files (
.Pa /etc/ppp/pap-secrets
for PAP,
.Pa /etc/ppp/chap-secrets
for CHAP).
Both secrets files have the same format.
The secrets files can contain secrets for
.Nm
to use in authenticating itself to other
systems, as well as secrets for
.Nm
to use when authenticating other systems to itself.
.Pp
Each line in a secrets file contains one secret.
A given secret is
specific to a particular combination of client and server \(em 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.
.Pp
A secrets file is parsed into words as for an options file, so the
client name, server name and secrets fields must each be one word,
with any embedded spaces or other special characters quoted or
escaped.
Any following words on the same line are taken to be a list
of acceptable IP addresses for that client, or an
override for
.Sy local:remote
addresses (the same format used on the
command line or in the options file) when on a line that contains a
specific client name (not a wildcard nor empty).
If there are only 3 words
on the line, or if the first word is
.Dq \- ,
then all IP addresses are disallowed.
To allow any address, use
.Dq * .
A word starting with
.Dq !
indicates that the specified address is not acceptable.
An address may be followed by
.Dq /
and a number
.Ar number ,
to indicate a whole subnet, i.e. all addresses which have the same
value in the most significant
.Ar number
bits.
Note that case is significant in the client and server names
and in the secret.
.Pp
If the secret starts with an
.Dq @ ,
what follows is assumed to be the
name of a file from which to read the secret.
A
.Dq *
as the client or server name matches any name.
When selecting a secret,
.Nm
takes the best match, i.e. the match with the fewest wildcards.
.Pp
Thus a secrets file contains both secrets for use in authenticating
other hosts, plus secrets which we use for authenticating ourselves to
others.
When
.Nm
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
.Cm domain
option is used.
This default can be overridden with the
.Cm name
option, except when the
.Cm usehostname
option is used.
.Pp
When
.Nm
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
.Cm user
option.
If this option is not used, the name defaults to
the name of the local system, determined as described in the previous
paragraph.
Then
.Nm
looks for a secret with this name in the first
field and the peer's name in the second field.
.Nm
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,
.Nm
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
.Cm remotename
option.
Otherwise, if the remote IP address
was specified by a name (rather than in numeric form), that name will
be used as the peer's name.
Failing that,
.Nm
will use the null string as the peer's name.
.Pp
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
.Xr crypt 3
and checked against the secret again.
Thus secrets for authenticating the
peer can be stored in encrypted form if desired.
If the
.Cm papcrypt
option is given, the first (unencrypted) comparison is
omitted, for better security.
.Pp
Furthermore, if the
.Cm login
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
.Cm login
option, the secret in
.Pa /etc/ppp/pap-secrets
would be
.Dq \&"\&" ,
which will match any password supplied by the peer.
This avoids the need to have the same secret in two places.
.Pp
Additional checks are performed when the
.Cm login
option is used.
If the file
.Pa /etc/ppp/ppp.deny
exists, and the user is listed in it, the authentication fails.
If the file
.Pa /etc/ppp/ppp.shells
exists and
the user's normal login shell is not listed, the authentication fails.
.Pp
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,
.Nm
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.
.Pp
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,
.Nm
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.
.Ss ROUTING
When IPCP negotiation is completed successfully,
.Nm
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
.Cm defaultroute
and/or
.Cm proxyarp
options are sufficient for this, but in some cases
further intervention is required.
The
.Pa /etc/ppp/ip-up
script can be used for this.
.Pp
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
.Cm defaultroute
option causes
.Nm
to create such a default route when IPCP comes up, and
delete it when the link is terminated.
.Pp
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
.Cm proxyarp
option causes
.Nm
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,
.Nm
creates a
permanent, published ARP entry with the IP address of the remote host
and the hardware address of the network interface found.
.Pp
When the
.Cm demand
option is used, the interface IP addresses have
already been set at the point when IPCP comes up.
If
.Nm
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),
.Nm
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 ENVIRONMENT
The environment variables that
.Nm
sets are:
.Bl -tag -width "PEERNAME"
.It Ev DEVICE
The name of the serial tty device being used.
.It Ev IFNAME
The name of the network interface being used.
.It Ev IPLOCAL
The IP address for the local end of the link.
This is only set when IPCP has come up.
.It Ev IPREMOTE
The IP address for the remote end of the link.
This is only set when IPCP has come up.
.It Ev PEERNAME
The authenticated name of the peer.
This is only set if the peer authenticates itself.
.It Ev SPEED
The baud rate of the tty device.
.It Ev UID
The real user-id of the user who invoked
.Nm .
.El
.Sh FILES
.Nm
reads options from the files
.Pa /etc/ppp/options ,
.Pa ~/.ppprc
and
.Pa /etc/ppp/options. Ns Ar tty_name
(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
.Pa options. Ns Ar tty_name
file is read.)
.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
.Cm file
or
.Cm call
options within an options file.
.Bl -tag -width ".Pa /usr/share/examples/pppd/"
.It Pa /var/run/ppp Ns Ar unit Ns \&.pid
Process-ID for
.Nm
process on ppp interface
.Ar unit .
.It Pa /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.
.Nm
will log a warning if this is not the case.
.It Pa /etc/ppp/chap-secrets
Names, secrets and IP addresses for CHAP authentication.
As for
.Pa /etc/ppp/pap-secrets ,
this file should be owned by root and not
readable or writable by any other user.
.Nm
will log a warning if this is not the case.
.It Pa /etc/ppp/options
System default options for
.Nm ,
read before user default options or
command-line options.
.It Pa ~/.ppprc
User default options, read before
.Pa /etc/ppp/options. Ns Ar tty_name .
.It Pa /etc/ppp/options. Ns Ar tty_name
System default options for the serial port being used, read after
.Pa ~/.ppprc .
In forming the
.Ar tty_name
part of this filename, an initial
.Dq /dev/
is stripped from the port name (if present), and any slashes in the
remaining part are converted to dots.
.It Pa /etc/ppp/peers
A directory containing options files which may contain privileged
options, even if
.Nm
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.
.It Pa /etc/ppp/ppp.deny
Lists users who may not use the system password PAP authentication.
.It Pa /etc/ppp/ppp.shells
Lists user shells which are approved for system password PAP authentication
logins.
.It Pa /usr/share/examples/pppd/
Sample
.Nm
configuration files.
.El
.Pp
.Nm
also 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.
.Nm
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.
.Nm
runs the scripts with
standard input, output and error redirected to
.Pa /dev/null ,
and with an
environment that is empty except for some environment variables that
give information about the link.
.Nm
invokes the following scripts, if they exist.
It is not an error if they don't exist.
.Bl -tag -width ".Pa /etc/ppp/auth-down"
.It Pa /etc/ppp/auth-up
A program or script which is executed after the remote system
successfully authenticates itself.
It is executed with the following parameters:
.Pp
.Sy iface-name peer-name user-name tty-dev speed
.Pp
Note that this script is not executed if the peer doesn't authenticate
itself, for example when the
.Cm noauth
option is used.
.It Pa /etc/ppp/auth-down
A program or script which is executed when the link goes down, if
.Pa /etc/ppp/auth-up
was previously executed.
It is executed in the same manner with the same parameters as
.Pa /etc/ppp/auth-up .
.It Pa /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 following parameters:
.Pp
.Sy iface-name tty-dev speed local-IP remote-IP ipparam
.It Pa /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
.Pa /etc/ppp/ip-up
script.
It is invoked in the same manner and with the same parameters.
.It Pa /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 following parameters:
.Pp
.Sy iface-name tty-dev speed network-number
.Sy local-IPX-node-address remote-IPX-node-address
.Sy local-IPX-routing-proto remote-IPX-routing-proto
.Sy local-IPX-router-name remote-IPX-router-name
.Sy ipparam pppd-pid
.Pp
The local-IPX-routing-protocol and remote-IPX-routing-protocol field
may be one of the following:
.Bl -hang
.It Dq NONE
to indicate that there is no routing protocol
.It Dq RIP
to indicate that RIP/SAP should be used
.It Dq NLSP
to indicate that Novell NLSP should be used
.It Dq RIP NLSP
to indicate that both RIP/SAP and NLSP should be used
.El
.It Pa /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
.Pa /etc/ppp/ipx-up
script.
It is invoked in the same manner and with the same parameters.
.El
.Sh EXAMPLES
The following examples assume that the
.Pa /etc/ppp/options
file contains the
.Cm auth
option (as in the default
.Pa /etc/ppp/options
file in the ppp distribution).
.Pp
Probably the most common use of
.Nm
is to dial out to an ISP.
This can be done with a command such as
.Bd -literal -offset indent
# pppd call isp
.Ed
.Pp
where the
.Pa /etc/ppp/peers/isp
file is set up by the system
administrator to contain something like this:
.Bd -literal -offset indent
ttyS0 19200 crtscts
connect '/usr/sbin/chat -v -f /etc/ppp/chat-isp'
noauth
.Ed
.Pp
In this example, we are using chat to dial the ISP's modem and go
through any logon sequence required.
The
.Pa /etc/ppp/chat-isp
file contains the script used by chat; it could for example contain
something like this:
.Bd -literal -offset indent
ABORT "NO CARRIER"
ABORT "NO DIALTONE"
ABORT "ERROR"
ABORT "NO ANSWER"
ABORT "BUSY"
ABORT "Username/Password Incorrect"
"" "at"
OK "at&d0&c1"
OK "atdt2468135"
"name:" "^Umyuserid"
"word:" "\\qmypassword"
"ispts" "\\q^Uppp"
"~-^Uppp-~"
.Ed
.Pp
See the
.Xr chat 8
man page for details of chat scripts.
.Pp
.Nm
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
.Nm
(installed setuid-root) with a command such as
.Bd -literal -offset indent
# pppd proxyarp
.Ed
.Pp
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
.Pa /etc/ppp/pap-secrets
or
.Pa /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
.Sy joespc
which is to be allowed to dial in to the machine called
.Sy server
and use the IP address
.Sy joespc.my.net ,
you would add an entry like this to
.Pa /etc/ppp/pap-secrets
or
.Pa /etc/ppp/chap-secrets :
.Bd -literal -offset indent
joespc  server  "joe's secret"  joespc.my.net
.Ed
.Pp
Alternatively, you can create a username called (for example)
.Sy ppp ,
whose login shell is
.Nm
and whose home directory is
.Pa /etc/ppp .
Options to be used when
.Nm
is run this way can be put in
.Pa /etc/ppp/.ppprc .
.Pp
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
.Cm asyncmap Li a0000 .
If the path includes a telnet, you probably should escape ^] as well
.Pq Cm asyncmap Li 200a0000 .
If the path includes an rlogin, you will need to use the
.Cm escape Li ff
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
Messages are sent to the syslog daemon using facility
.Dv LOG_DAEMON .
(This can be overridden by recompiling
.Nm
with the macro
.Dv LOG_PPP
defined as the desired facility.)
In order to see the error and debug messages, you will need to edit your
.Pa /etc/syslog.conf
file to direct the messages to the desired output device or file.
.Pp
The
.Cm debug
option causes the contents of all control packets sent
or received to be logged, that is, all LCP, PAP, CHAP or IPCP packets.
This can be useful if the PPP negotiation does not succeed or if
authentication fails.
If debugging is enabled at compile time, the
.Cm debug
option also causes other debugging messages to be logged.
.Pp
Debugging can also be enabled or disabled by sending a
.Dv SIGUSR1
signal to the
.Nm
process.
This signal acts as a toggle.
.Sh SEE ALSO
.Xr tcpdump 1 ,
.Xr crypt 3 ,
.Xr syslog.conf 5 ,
.Xr chat 8 ,
.Xr ppp 8 ,
.Xr syslogd 8
.Sh STANDARDS
.Rs
.%A V. Jacobson
.%D February 1990
.%R RFC 1144
.%T Compressing TCP/IP headers for low-speed serial links
.Re
.Pp
.Rs
.%A R. Rivest
.%D April 1992
.%R RFC 1321
.%T The MD5 Message-Digest Algorithm
.Re
.Pp
.Rs
.%A G. McGregor
.%D May 1992
.%R RFC 1332
.%T PPP Internet Protocol Control Protocol (IPCP)
.Re
.Pp
.Rs
.%A B. Lloyd
.%A W.A. Simpson
.%D October 1992
.%R RFC 1334
.%T PPP authentication protocols
.Re
.Pp
.Rs
.%A W.A. Simpson
.%D July 1994
.%R RFC 1661
.%T The Point-to-Point Protocol (PPP)
.Re
.Pp
.Rs
.%A W.A. Simpson
.%D July 1994
.%R RFC 1662
.%T PPP in HDLC-like Framing
.Re
.Sh AUTHORS
.An -nosplit
.Nm
was written by
.An Paul Mackerras Aq Mt Paul.Mackerras@cs.anu.edu.au ,
based on earlier work by
.An Drew Perkins ,
.An Brad Clements ,
.An Karl Fox ,
.An Greg Christy ,
and
.An Brad Parker .