PPPD(1M) Maintenance Commands PPPD(1M)

NAME

pppd - point to point protocol daemon

SYNOPSIS

pppd [tty_name] [speed] [options]

DESCRIPTION

The point-to-point protocol (PPP) provides a method for transmitting
datagrams over serial point-to-point links. PPP is composed of three
components: a facility for encapsulating datagrams over serial links, an
extensible link control protocol (LCP), and a family of network control
protocols (NCP) for establishing and configuring different network-layer
protocols.


The encapsulation scheme is provided by driver code in the kernel. pppd
provides the basic LCP authentication support and several NCPs for
establishing and configuring the Internet Protocol (referred to as the IP
Control Protocol or "IPCP") and IPv6 (IPV6CP).

OPTIONS

The following sections discuss the pppd options:

Options Files

Options are taken from files and the command line. pppd reads options
from the files /etc/ppp/options, $HOME/.ppprc and
/etc/ppp/options.ttyname (in that order) before processing the options on
the command line. (Command-line options are scanned for the terminal name
before the options.ttyname file is read.) To form the name of the
options.ttyname file, the initial /dev/ is removed from the terminal
name, and any remaining forward slash characters (/) are replaced with
dots. For example, with serial device /dev/cua/a, option file
/etc/ppp/options.cua.a is read.


An options file is parsed into a series of words that are delimited by
whitespace. Whitespace can be included in a word by enclosing the word in
double-quotes ("). A backslash (\) quotes the succeeding character. A
hash (#) starts a comment, which continues until the end of the line.
There is no restriction on using the file or call options within an
options file.

Frequently Used Options

<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 uses that
terminal and does not fork to put itself in the
background. A value for this option from a
privileged source cannot be overridden by a non-
privileged user.


<speed>
Set the baud rate to <speed> (a decimal number).
The default is to leave the baud rate unchanged.
This option is normally needed for dial-out only.


asyncmap <map>
Set the async character map to <map>. The map
describes which control characters cannot be
successfully received over the serial line. pppd
asks 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 asyncmap options are
given, the values are ORed together. If no
asyncmap option is given, pppd attempts to
negotiate a value of 0. If the peer agrees, this
disables escaping of the standard control
characters. Use the default-asyncmap option to
disable negotiation and escape all control
characters.


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 the auth or the noauth option
is not specified, pppd allows the peer to use only
those IP addresses to which the system does not
already have a route.


call name
Read options from the file /etc/ppp/peers/name.
This file may contain privileged options,
including noauth, even if pppd is not being run by
root. The name string may not begin with a slash
("/") or include consecutive periods ("..") as a
pathname component.


callback number
Request a callback to the given telephone number
using Microsoft CBCP.


connect script
Use the executable or shell command specified by
script to set up the serial line. This script
would typically use the chat(1M) program to dial
the modem and start the remote PPP session. A
value for this option originating from a
privileged source cannot be overridden by a non-
privileged user.


crtscts
Use hardware flow control, that is, RTS/CTS, to
control the flow of data on the serial port. If
the crtscts, nocrtscts, cdtrcts or nocdtrcts
option is not provided, the hardware flow control
setting for the serial port is left unchanged.
Some serial ports lack a true RTS output and use
this mode to implement unidirectional flow
control. The serial port suspends transmission
when requested by the modem by means of CTS but
cannot request the modem to stop sending to the
computer. This mode allows the use of DTR as a
modem control line.


defaultroute
Add a default route to the system routing tables
when IPCP negotiation successfully completes,
using the peer as the gateway. This entry is
removed when the PPP connection is broken. This
option is privileged if the nodefaultroute option
is specified.


disconnect script
Run the executable or shell command specified by
script after pppd terminates the link. Typically,
this script is used to command the modem to hang
up if hardware modem control signals are not
available. disconnect is not run if the modem has
already hung up. A value for this option
originating from a privileged source cannot be
overridden by a non-privileged user.


escape xx,yy,...
Specifies that certain characters 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 escape option, unlike the
asyncmap option which allows only control
characters to be specified. Characters that cannot
be escaped are those containing hex values 0x20
through 0x3f and 0x5e.


file name
Read options from file name. If this option is
used on the command line or in $HOME/.ppprc, the
file must be readable by the user invoking pppd.
See for a list of files that pppd always reads,
regardless of the use of this option.


init script
Run the executable or shell command specified by
script to initialize the serial line. This script
would typically use the chat(1M) program to
configure the modem to enable auto-answer. A value
for this option from a privileged source cannot be
overridden by a non-privileged user.


lock
Directs pppd to create a UUCP-style lock file for
the serial device to ensure exclusive access to
the device.


mru n
Set the Maximum Receive Unit (MRU) value to n.
pppd asks the peer to send packets of no more than
n bytes. Minimum MRU value is 128. Default MRU
value is 1500. A value of 296 is recommended for
slow links (40 bytes for TCP/IP header + 256 bytes
of data). For IPv6, MRU must be at least 1280.


mtu n
Set the Maximum Transmit Unit (MTU) value to n.
Unless the peer requests a smaller value via MRU
negotiation, pppd requests the kernel networking
code to send data packets of no more than n bytes
through the PPP network interface. For IPv6, MTU
must be at least 1280.


passive
Enables the "passive" option in the LCP. With this
option, pppd attempts to initiate a connection; if
no reply is received from the peer, pppd waits
passively for a valid LCP packet instead of
exiting, as it would without this option.

Options

<local_IP_address>:<remote_IP_address>

Set the local and/or remote interface IP addresses. Either one may be
omitted, but the colon is required. The IP addresses are specified
with a host name or in decimal dot notation, for example: :10.1.2.3.
The default local address is the first IP address of the system
unless the noipdefault option is provided. The remote address is
obtained from the peer if not specified in any option. Thus, in
simple cases, this option is not required. If a local and/or remote
IP address is specified with this option, pppd will not accept a
different value from the peer in the IPCP negotiation unless the
ipcp-accept-local and/or ipcp-accept-remote options are given,
respectively.


allow-fcs fcs-type

Set allowable FCS type(s) for data sent to the peer. The fcs-type is
a comma-separated list of "crc16", "crc32", "null", or integers. By
default, all known types are allowed. If this option is specified and
the peer requests a type not listed, a LCP Configure-Nak is sent to
request only the listed types.


allow-ip address(es)

Allow peers to use the given IP address or subnet without
authenticating themselves. The parameter is parsed in the same manner
as each element of the list of allowed IP addresses is parsed in the
secrets files. See the section more more details.


bsdcomp nr,nt

Request that the peer compress packets that it sends using the BSD-
Compress scheme, with a maximum code size of nr bits, and agree to
compress packets sent to the peer with a maximum code size of nt
bits. If nt is not specified, it defaults to the value given for nr.
Values in the range 9 to 15 may be used for nr and nt; larger values
provide better compression but consume more kernel memory for
compression dictionaries. Alternatively, a value of 0 for nr or nt
disables compression in the corresponding direction. Use nobsdcomp or
bsdcomp 0 to disable BSD-Compress compression entirely. If this
option is read from a privileged source, a nonprivileged user may not
specify a code size larger than the value from the privileged source.


cdtrcts

Use a non-standard hardware flow control such as DTR/CTS to control
the flow of data on the serial port. If the crtscts, nocrtscts,
cdtrcts or nocdtrcts option is not specified, the hardware flow
control setting for the serial port is left unchanged. Some serial
ports lack a true RTS output. Such serial ports use this mode to
implement true bi-directional flow control. Note that this flow
control mode does not permit using DTR as a modem control line.


chap-interval n

If this option is given, pppd will rechallenge the peer every n
seconds.


chap-max-challenge n

Set the maximum number of CHAP challenge transmissions to n (default
10).


chap-restart n

Set the CHAP restart interval (retransmission timeout for challenges)
to n seconds. The default is 3.


connect-delay n

Wait for up to n milliseconds after the connect script finishes for a
valid PPP packet from the peer. When the wait period elapses or when
a valid PPP packet is received from the peer, pppd begins negotiation
by sending its first LCP packet. The default value is 1000 (1
second). A wait period applies only if the connect or pty option is
used.


datarate n

Set maximum data rate to n (in bytes per second) when using the pty,
notty, record, or socket options.


debug

Enables connection debugging facilities. If this option is given,
pppd logs the contents of all control packets sent or received in a
readable form. The packets are logged through syslog with facility
daemon and level debug. This information can be directed to a file by
configuring /etc/syslog.conf appropriately.


default-asyncmap

Disable asyncmap negotiation, forcing all control characters to be
escaped for both the transmit and the receive direction.


default-fcs

Disable FCS Alternatives negotiation entirely. By default, no FCS
Alternatives option is sent to the peer, but the option is accepted.
If this option is specified by the peer, then LCP Configure-Reject is
sent.


default-mru

Disable MRU [Maximum Receive Unit] negotiation. With this option,
pppd uses the default MRU value of 1500 bytes for the transmit and
receive directions.


deflate nr,nt,e

Request that the peer compress packets that it sends, using the
deflate scheme, with a maximum window size of 2**nr bytes, and agree
to compress packets sent to the peer with a maximum window size of
2**nt bytes and effort level of e (1 to 9). If nt is not specified,
it defaults to the value given for nr. If e is not specified, it
defaults to 6. Values in the range 9 to 15 may be used for nr and
nt; larger values provide better compression but consume more kernel
memory for compression dictionaries. (Value 8 is not permitted due to
a zlib bug.) Alternatively, a value of 0 for nr or nt disables
compression in the corresponding direction. Use nodeflate or deflate
0 to disable deflate compression entirely. (Note: pppd requests
deflate compression in preference to BSD-Compress if the peer can do
either.) If this option is read from a privileged source, a
nonprivileged user may not specify a code size larger than the value
from the privileged source.


demand

Initiate the link only on demand, that is, 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 initially
configures and enables the interface for IP traffic without
connecting to the peer. When traffic is available, pppd connects to
the peer and performs negotiation, authentication and other actions.
When completed, pppd passes data packets across the link. The demand
option implies the persist option. If this behavior is not desired,
use the nopersist option after the demand option. The idle and
holdoff options can be used in conjunction with the demand option.


domain 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 could
specify domain Quotron.COM. With this configuration, pppd uses the
name porsche.Quotron.COM for accessing secrets in the secrets file
and as the default name when authenticating to the peer. This option
is privileged.


endpoint endpoint-value

Set the endpoint discriminator (normally used for RFC 1990 Multilink
PPP operation). The endpoint-value consists of a class identifier and
a class-dependent value. The class identifier is one of "null,"
"local," "IP," "MAC," "magic," "phone," or a decimal integer. If
present, the class-dependent value is separated from the identifier
by a colon (":") or period (".") . This value may be a standard
dotted-decimal IP address for class "IP," an optionally colon-or-dot
separated hex Ethernet address for class "MAC" (must have 6 numbers),
or an arbitrary string of bytes specified in hex with optional colon
or dot separators between bytes. Although this option is available,
this implementation does not support multilink.


fcs fcs-type

Set FCS type(s) desired for data sent by the peer. The fcs-type is a
comma-separated list of crc16, crc32, null, or integers. By default,
an FCS Alternatives option is not specified, and the medium-dependent
FCS type is used. If this option is specified and the peer sends an
LCP Configure-Nak, only the listed types are used. If none are in
common, the FCS Alternatives option is omitted from the next LCP
Configure-Request to drop back to the default.


hide-password

When logging the contents of PAP packets, this option causes pppd to
exclude the password string from the log. This is the default.


holdoff n

Specifies how many seconds to wait before re-initiating the link
after it terminates. This option is effective only if the persist or
demand option is used. The holdoff period is not applied if the link
is terminated because it was idle.


ident string

Set the LCP Identification string. The default value is a version
string similar to that displayed by the --version option.


idle n

Specifies that pppd must disconnect if the link is idle for n
seconds. The link is idle when no data packets (i.e. IP packets) are
being sent or received. Do not use this option with the persist
option but without the demand option.


ipcp-accept-local

With this option, pppd accepts the peer's idea of the local IP
address, even if the local IP address is specified in an option.


ipcp-accept-remote

With this option, pppd accepts the peer's idea of its remote IP
address, even if the remote IP address is specified in an option.


ipcp-max-configure n

Set the maximum number of IPCP Configure-Request transmissions to n
(default 10).


ipcp-max-failure n

Set the maximum number of IPCP Configure-NAKs sent before sending
Configure-Rejects instead to n (default 10).


ipcp-max-terminate n

Set the maximum number of IPCP terminate-request transmissions to n
(default 3).


ipcp-restart n

Set the IPCP restart interval (retransmission timeout) to n seconds
(default 3).


ipparam string

Provides an extra parameter to the ip-up and ip-down scripts. When
this option is given, the string supplied is given as the sixth
parameter to those scripts. See the section.


ipv6 <local_interface_identifier>,<remote_interface_identifier>

Set the local and/or remote 64-bit interface identifier. Either one
may be omitted. The identifier must be specified in standard ASCII
notation of IPv6 addresses (for example: ::dead:beef). If the ipv6cp-
use-ipaddr option is given, the local and remote identifiers are
derived from the respective IPv4 addresses (see above). The ipv6cp-
use-persistent option can be used instead of the ipv6
<local>,<remote> option.


ipv6cp-accept-local

Accept peer's interface identifier for the local link identifier.


ipv6cp-max-configure n

Set the maximum number of IPv6CP Configure-Request transmissions to n
(default 10).


ipv6cp-max-failure n

Set the maximum number of IPv6CP Configure-NAKs sent before sending
Configure-Rejects instead to n (default 10).


ipv6cp-max-terminate n

Set the maximum number of IPv6CP terminate-request transmissions to n
(default 3).


ipv6cp-restart n

Set the IPv6CP restart interval (retransmission timeout) to n seconds
(default 3).


ipv6cp-use-ipaddr

If either the local or remote IPv6 address is unspecified, use the
corresponding configured IPv4 address as a default interface
identifier. (This option uses the configured addresses, not the
negotiated addresses. Do not use it with ipcp-accept-local if the
local IPv6 identifier is unspecified or with ipcp-accept-remote if
the remote IPv6 identifier is unspecified.)


ipv6cp-use-persistent

Use uniquely-available persistent value for link local address.


kdebug n

Enable debugging code in the kernel-level PPP driver. Argument n is
the sum of the following values: 1 to enable general debug messages,
2 to request that contents of received packets be printed, and 4 to
request contents of transmitted packets be printed. Messages printed
by the kernel are logged by syslogd(1M) to a file directed in the
/etc/syslog.conf configuration file. Do not use the kdebug option to
debug failed links. Use the debug option instead.


lcp-echo-failure n

If this option is given, pppd presumes the peer to be dead if n LCP
Echo-Requests are sent without receiving a valid LCP Echo-Reply. If
this happens, pppd terminates the connection. This option requires a
non-zero value for the lcp-echo-interval parameter. This option
enables pppd to terminate after the physical connection is broken
(for example, if the modem has hung up) in situations where no
hardware modem control lines are available.


lcp-echo-interval n

If this option is given, pppd sends an LCP Echo-Request frame to the
peer every n seconds. Normally the peer responds to the Echo-Request
by sending an Echo-Reply. This option can be used with the lcp-echo-
failure option to detect that the peer is no longer connected.


lcp-max-configure n

Set the maximum number of LCP Configure-Request transmissions to n
(default 10).


lcp-max-failure n

Set the maximum number of LCP Configure-NAKs sent before starting to
send Configure-Rejects instead to n (default 10).


lcp-max-terminate n

Set the maximum number of LCP Terminate-Request transmissions to n
(default 3).


lcp-restart n

Set the LCP restart interval (retransmission timeout) to n seconds
(default 3).


linkname name

Sets the logical name of the link to name. pppd creates a file named
ppp-name.pid in /var/run containing its process ID. This is useful in
determining which instance of pppd is responsible for the link to a
given peer system. This is a privileged option.


local

Do not use modem control lines. With this option, pppd ignores the
state of the CD (Carrier Detect) signal from the modem and does not
change the state of the DTR (Data Terminal Ready) signal.


logfd n

Send log messages to file descriptor n. pppd sends log messages to
(at most) one file or file descriptor (as well as sending the log
messages to syslog), so this option and the logfile option are
mutually exclusive. By default pppd sends log messages to stdout
(file descriptor 1) unless the serial port is open on stdout.


logfile filename

Append log messages to the file filename (and send the log messages
to syslog). The file is opened in append mode with the privileges of
the user who invoked pppd.


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 and the system
password database to be allowed access.


maxconnect n

Terminate the connection after it has been available for network
traffic for n seconds (that is, n seconds after the first network
control protocol starts). An LCP Time-Remaining message is sent when
the first NCP starts, and again when 5, 2, and 0.5 minutes are
remaining.


maxfail n

Terminate after n consecutive failed connection attempts. A value of
0 means no limit. The default value is 10.


modem

Use the modem control lines. This option is the default. With this
option, pppd waits for the CD (Carrier Detect) signal from the modem
to be asserted when opening the serial device (unless a connect
script is specified), and drops the DTR (Data Terminal Ready) signal
briefly when the connection is terminated and before executing the
connect script.


ms-dns <addr>

If pppd is acting as a server for Microsoft Windows clients, this
option allows pppd to supply one or two DNS (Domain Name Server)
addresses to the clients. The first instance of this option specifies
the primary DNS address; the second instance (if given) specifies the
secondary DNS address. If the first instance specifies a name that
resolves to multiple IP addresses, then the first two addresses are
used. (This option is present in some older versions of pppd under
the name dns-addr.)


ms-lanman

If pppd connects as a client to a Microsoft server and uses MS-CHAPv1
for authentication, this option selects the LAN Manager password
style instead of Microsoft NT.


ms-wins <addr>

If pppd acts 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. As with ms-dns, if the
name specified resolves to multiple IP addresses, then the first two
will be taken as primary and secondary.


name name

Set the name of the local system for authentication purposes to name.
This is a privileged option. With this option, pppd uses lines in the
secrets files that have name as the second field to look for a secret
to use in authenticating the peer. In addition, unless overridden
with the user option, name is used as the name to send to the peer
when authenticating the local system. (Note that pppd does not append
the domain name to name.)


no-accm-test

Disable use of asyncmap (ACCM) checking using LCP Echo-Request
messages. If the lcp-echo-failure is used on an asynchronous line,
pppd includes all control characters in the first n LCP Echo-Request
messages. If the asyncmap is set incorrectly, the link drops rather
than continue operation with random failures. This option disables
that feature.


noaccomp

Disable HDLC Address/Control compression in both directions (send and
receive).


noauth

Do not require the peer to authenticate itself. This option is
privileged.


nobsdcomp

Disables BSD-Compress compression; pppd will not request or agree to
compress packets using the BSD-Compress scheme. This option is not
necessary if noccp is specified.


noccp

Disable CCP (Compression Control Protocol) negotiation. This option
should only be required if the peer has bugs or becomes confused by
requests from pppd for CCP negotiation. If CCP is disabled, then BSD
and deflate compression do not need to be separately disabled.


nocrtscts

Disable hardware flow control (i.e. RTS/CTS) on the serial port. If
the crtscts, nocrtscts, cdtrcts or nocdtrcts options are not given,
the hardware flow control setting for the serial port is left
unchanged.


nocdtrcts

This option is a synonym for nocrtscts. Either option will disable
both forms of hardware flow control.


nodefaultroute

Disable the defaultroute option. You can prevent non-root users from
creating default routes with pppd by placing this option in the
/etc/ppp/options file.


nodeflate

Disables deflate compression; pppd will not request or agree to
compress packets using the deflate scheme. This option is not
necessary if noccp is specified.


nodeflatedraft

Do not use Internet Draft (incorrectly assigned) algorithm number for
deflate compression. This option is not necessary if noccp is
specified.


nodetach

Do not detach from the controlling terminal. Without this option,
pppd forks to become a background process if a serial device other
than the terminal on the standard input is specified.


noendpoint

Do not send or accept the Multilink Endpoint Discriminator option.


noident

Disable use of LCP Identification. LCP Identification messages will
not be sent to the peer, but received messages will be logged.
(Specify this option twice to completely disable LCP Identification.
In this case, pppd sends LCP Code-Reject in response to received LCP
Identification messages.)


noip

Disable IPCP negotiation and IP communication. Use this option only
if the peer has bugs or becomes confused by requests from pppd for
IPCP negotiation.


noipv6

Disable IPv6CP negotiation and IPv6 communication. IPv6 is not
enabled by default.


noipdefault

Disables the default behavior 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 must supply the local IP address
during IPCP negotiation (unless it specified explicitly on the
command line or in an options file).


nolog

Do not send log messages to a file or file descriptor. This option
cancels the logfd and logfile options. nologfd acts as an alias for
this option.


nomagic

Disable magic number negotiation. With this option, pppd cannot
detect a looped-back line. Use this option only if the peer has bugs.
Do not use this option to work around the "Serial line is looped
back" error message.


nopam

This privileged option disables use of pluggable authentication
modules. If this option is specified, pppd reverts to standard
authentication mechanisms. The default is not to use PAM.


nopcomp

Disable protocol field compression negotiation in the receive and the
transmit direction.


nopersist

Exit once a connection has been made and terminated. This is the
default unless the persist or demand option is specified.


noplink

Cause pppd to use I_LINK instead of I_PLINK. This is the default.
When I_LINK is used, the system cleans up terminated interfaces (even
when SIGKILL is used) but does not allow ifconfig(1M) to unplumb PPP
streams or insert or remove modules dynamically. Use the plink option
if ifconfig(1M) modinsert, modremove or unplumb support is needed.


nopredictor1

Do not accept or agree to Predictor-1 compression. (This option is
accepted for compatibility. The implementation does not support
Predictor-1 compression.)


noproxyarp

Disable the proxyarp option. If you want to prevent users from
creating proxy ARP entries with pppd, place this option in the
/etc/ppp/options file.


notty

Normally, pppd requires a terminal device. With this option, pppd
allocates itself a pseudo-tty master/slave pair and uses the slave as
its terminal device. pppd creates a child process to act as a
character shunt to transfer characters between the pseudo-tty master
and its standard input and output. Thus, pppd transmits characters on
its standard output and receives characters on its standard input
even if they are not terminal devices. This option increases the
latency and CPU overhead of transferring data over the ppp interface
as all of the characters sent and received must flow through the
character shunt process. An explicit device name may not be given if
this option is used.


novj

Disable Van Jacobson style TCP/IP header compression in both the
transmit and the receive direction.


novjccomp

Disable the connection-ID compression option in Van Jacobson style
TCP/IP header compression. With this option, pppd does not omit the
connection-ID byte from Van Jacobson compressed TCP/IP headers, nor
does it ask the peer to do so. This option is unnecessary if novj is
specified.


pam

This privileged option enables use of PAM. If this is specified, pppd
uses the pam(3PAM) framework for user authentication with a service
name of "ppp" if the login option and PAP authentication are used.
The default is not to use PAM.


papcrypt

Indicates that pppd should not accept a password which, before
encryption, is identical to the secret from the /etc/ppp/pap-secrets
file. Use this option if the secrets in the pap-secrets file are in
crypt(3C) format.


pap-max-authreq n

Set the maximum number of PAP authenticate-request transmissions to n
(default 10).


pap-restart n

Set the PAP restart interval (retransmission timeout) to n seconds
(default 3).


pap-timeout n

Set the maximum time that pppd waits for the peer to authenticate
itself with PAP to n seconds (0= no limit). The default is 30
seconds.


password string

Password string for authentication to the peer.


persist

Do not exit after a connection is terminated; instead try to reopen
the connection.


plink

Cause pppd to use I_PLINK instead of I_LINK. The default is to use
I_LINK, which cleans up terminated interface (even if SIGKILL is
used), but does not allow ifconfig(1M) to unplumb PPP streams or
insert or remove modules dynamically. Use this option if ifconfig(1M)
modinsert/modremove/unplumb support is needed. See also the plumbed
option.


plugin filename

Load the shared library object file filename as a plugin. This is a
privileged option. Unless the filename specifies an explicit path,
/etc/ppp/plugins and /usr/lib/inet/ppp will be searched for the
object to load in that order.


plumbed

This option indicates that pppd should find a plumbed interface and
use that for the session. If IPv4 addresses or IPv6 interface IDs or
link MTU are otherwise unspecified, they are copied from the
interface selected. This mode mimics some of the functionality of the
older aspppd implementation and may be helpful when pppd is used with
external applications that use ifconfig(1M).


pppmux timer

Enable PPP Multiplexing option negotiation and set transmit
multiplexing timeout to timer microseconds.


privgroup group-name

Allows members of group group-name to use privileged options. This is
a privileged option. Because there is no guarantee that members of
group-name cannot use pppd to become root themselves, you should be
careful using this option. Consider it equivalent to putting the
members of group-name in the root or sys group.


proxyarp

Add an entry to the system's Address Resolution Protocol (ARP) table
with the IP address of the peer and the Ethernet address of this
system. When you use this option, the peer appears to other systems
to be on the local Ethernet. The remote address on the PPP link must
be in the same subnet as assigned to an Ethernet interface.


pty script

Specifies that the command script, and not a specific terminal device
is used for serial communication. pppd allocates itself a pseudo-tty
master/slave pair and uses the slave as its terminal device. script
runs in a child process with the pseudo-tty master as its standard
input and output. An explicit device name may not be given if this
option is used. (Note: if the record option is used in conjunction
with the pty option, the child process will have pipes on its
standard input and output.)


receive-all

With this option, pppd accepts all control characters from the peer,
including those marked in the receive asyncmap. Without this option,
pppd discards those characters as specified in RFC 1662. This option
should be used only if the peer has bugs, as is often found with
dial-back implementations.


record filename

Directs pppd to record all characters sent and received to a file
named filename. filename is opened in append mode, using the user's
user-ID and permissions. Because this option uses a pseudo-tty and a
process to transfer characters between the pseudo-tty and the real
serial device, it increases the latency and CPU overhead of
transferring data over the PPP interface. Characters are stored in a
tagged format with timestamps that can be displayed in readable form
using the pppdump(1M) program. This option is generally used when
debugging the kernel portion of pppd (especially CCP compression
algorithms) and not for debugging link configuration problems. See
the debug option.


remotename name

Set the assumed name of the remote system for authentication purposes
to name. Microsoft WindowsNT does not provide a system name in its
CHAP Challenge messages, and this option is often used to work around
this problem.


refuse-chap

With this option, pppd will not agree to authenticate itself to the
peer using standard Challenge Handshake Authentication Protocol
(CHAP). (MS-CHAP is not affected.)


refuse-mschap

Do not agree to authenticate to peer with MS-CHAPv1. If this option
is specified, requests for MS-CHAPv1 authentication from the peer are
declined with LCP Configure-Nak. That option does not disable any
other form of CHAP.


refuse-mschapv2

Do not agree to authenticate to peer with MS-CHAPv2. If specified,
this option requests that MS-CHAPv2 authentication from the peer be
declined with LCP Configure-Nak. That option does not disable any
other form of CHAP.


refuse-pap

With this option, pppd will not agree to authenticate itself to the
peer using Password Authentication Protocol (PAP).


require-chap

Require the peer to authenticate itself using standard CHAP
authentication. MS-CHAP is not affected.


require-mschap

Require the peer to authenticate itself using MS-CHAPv1
authentication.


require-mschapv2

Require the peer to authenticate itself using MS-CHAPv2
authentication.


require-pap

Require the peer to authenticate itself using PAP authentication.


show-password

When logging contents of PAP packets, this option causes pppd to show
the password string in the log message.


silent

With this option, pppd will not transmit LCP packets to initiate a
connection until a valid LCP packet is received from the peer. This
is like the "passive" option with older versions of pppd and is
retained for compatibility, but the current passive option is
preferred.


small-accm-test

When checking the asyncmap (ACCM) setting, pppd uses all 256 possible
values by default. See no-accm-test. This option restricts the test
so that only the 32 values affected by standard ACCM negotiation are
tested. This option is useful on very slow links.


socket host:port

Connect to given host and port using TCP and run PPP over this
connection.


sync

Use synchronous HDLC serial encoding instead of asynchronous. The
device used by pppd with this option must have sync support.
Currently supports zs, se, and hsi drivers.


unit n

Set PPP interface unit number to n, if possible.


updetach

With this option, pppd detaches from its controlling terminal after
establishing the PPP connection. When this is specified, messages
sent to stderr by the connect script, usually chat(1M), and debugging
messages from the debug option are directed to pppd's standard
output.


usehostname

Enforce the use of the hostname with domain name appended, if given,
as the name of the local system for authentication purposes. This
overrides the name option. Because the name option is privileged,
this option is normally not needed.


usepeerdns

Ask the peer for up to two DNS server addresses. Addresses supplied
by the peer, if any, are passed to the /etc/ppp/ip-up script in the
environment variables DNS1 and DNS2. In addition, pppd creates an
/etc/ppp/resolv.conf file containing one or two nameserver lines with
the address(es) supplied by the peer.


user name

Sets the name used for authenticating the local system to the peer to
name.


vj-max-slots n

Sets the number of connection slots to be used by the Van Jacobson
TCP/IP header compression and decompression code to n, which must be
between 2 and 16 (inclusive).


welcome script

Run the executable or shell command specified by script before
initiating PPP negotiation, after the connect script, if any, has
completed. A value for this option from a privileged source cannot be
overridden by a non-privileged user.


xonxoff

Use software flow control, that is, XON/XOFF, to control the flow of
data on the serial port.

Obsolete Options

The following options are obsolete:

+ua name
Read a PAP user name and password from the file name. This
file must have two lines for name and password. Name and
password are sent to the peer when the peer requests PAP
authentication.


+ipv6
Enable IPv6 and IPv6CP without specifying interface
identifiers.


--version
Show version number and exit.


--help
Show brief help message and exit.

EXTENDED DESCRIPTION

The following sections discuss miscellaneous features of pppd:

Security

pppd allows system administrators to provide legitimate users with PPP
access to a server machine without fear of compromising the security of
the server or the network it runs on. Access control is provided by
restricting IP addresses the peer may use based on its authenticated
identity (if any), and through restrictions on options a non-privileged
user may use. Options that permit potentially insecure configurations are
privileged. Privileged options are accepted only in files that are under
the control of the system administrator or when pppd is being run by
root.


By default, pppd allows 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, meaning all peers must authenticate
themselves to set up a connection. On such a system, the auth option is
the default. Conversely, a system with a PPP link that comprises the
only connection to the Internet probably does not possess a default
route, so the peer can use virtually any IP address without
authenticating itself.


Security-sensitive options are privileged and cannot be accessed by a
non-privileged user running pppd, either on the command line, in the
user's $HOME/.ppprc file, or in an options file read using the file
option. Privileged options may be used in /etc/ppp/options file or in an
options file read using the call option. If pppd is run by the root user,
privileged options can be used without restriction. If the
/etc/ppp/options file does not exist, then only root may invoke pppd. The
/etc/ppp/options file must be created (but may be empty) to allow
ordinary non-root users to access pppd.


When opening the device, pppd uses the invoking user's user ID or the
root UID (that is, 0), depending if 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 call 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 that they would not normally have access to. Otherwise pppd uses
the invoking user's real UID when opening the device.

Authentication

During the authentication process, one peer convinces the other of its
identity by sending its name and some secret information to the other.
During authentication, the first peer becomes the "client" and the second
becomes the "server." Authentication names can (but are not required to)
correspond to the peer's Internet hostnames.


pppd supports four authentication protocols: the Password Authentication
Protocol (PAP) and three forms of the Challenge Handshake Authentication
Protocol (CHAP). With the PAP protocol, the client sends its name and a
cleartext password to the server to authenticate itself. With CHAP, the
server initiates the authentication exchange by sending a challenge to
the client who must respond with its name and a hash value derived from
the shared secret and the challenge.


The PPP protocol is symmetrical, meaning that each peer may be required
to authenticate itself to the other. Different authentication protocols
and names can be used for each exchange.


By default, pppd authenticates if requested and does not require
authentication from the peer. However, pppd does not authenticate itself
with a specific protocol if it has no secrets that can do so.


pppd stores authentication secrets in the /etc/ppp/pap-secrets (for PAP),
and /etc/ppp/chap-secrets (for CHAP) files. Both files use the same
format. pppd uses secrets files to authenticate itself to other systems
and to authenticate other systems to itself.


Secrets files contain one secret per line. Secrets are specific to a
particular combination of client and server and can only be used by that
client to authenticate itself to that server. Each line in a secrets file
has a minimum of three fields that contain the client and server names
followed by the secret. Often, these three fields are followed by IP
addresses that are used by clients to connect to a server.


A secrets file is parsed into words, with client name, server name and
secrets fields allocated one word each. Embedded spaces or other special
characters within a word must be quoted or escaped. Case is significant
in all three fields.


A secret beginning with an at sign ("@") is followed by the name of a
file containing the secret. An asterisk (*) as the client or server name
matches any name. When choosing a match, pppd selects the one with the
fewest wildcards. Succeeding words on a line are interpreted by pppd as
acceptable IP addresses for that client. IP Addresses are disallowed if
they appear in lines that contain only three words or lines whose first
word begins with a hyphen ("-"). To allow any address, use "*". An
address starting with an exclamation point ("!") indicates that the
specified address is not acceptable. An address may be followed by "/"
and a number n to indicate a whole subnet (all addresses that have the
same value in the most significant n bits). In this form, the address may
be followed by a plus sign ("+") to indicate that one address from the
subnet is authorized, based on the ppp network interface unit number in
use. In this case, the host part of the address is set to the unit
number, plus one.


When authenticating the peer, pppd chooses a secret with the peer's name
in the first field of the secrets file and the name of the local system
in the second field. The local system name defaults to the hostname, with
the domain name appended if the domain option is used. The default can be
overridden with the name option unless the usehostname option is used.


When authenticating to the peer, pppd first determines the name it will
use to identify itself to the peer. This name is specified with the user
option. If the user option is not used, the name defaults to the host
name of the local system. pppd then selects a secret from the secrets
file by searching for an entry with a local name in the first field and
the peer's name in the second field. pppd will know the name of the peer
if standard CHAP authentication is used because the peer will have sent
it in the Challenge packet. However, if MS-CHAP or PAP is being used,
pppd must determine the peer's name from the options specified by the
user. The user can specify the peer's name directly with the 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.
If that fails, pppd uses the null string as the peer's name.


When authenticating the peer with PAP, the supplied password is compared
with data in the secrets file. If the password and secret do not match,
the password is encrypted using crypt() and checked against the secret
again. If the papcrypt option is given, the first unencrypted comparison
is omitted for better security, and entries must thus be in encrypted
crypt(3C) form.


If the login option is specified, the username and password are also
checked against the system password database. This allows you to set up
the pap-secrets file to enable PPP access only to certain users, and to
restrict the set of IP addresses available to users. Typically, when
using the login option, the secret in /etc/ppp/pap-secrets would be "",
which matches any password supplied by the peer. This makes having the
same secret in two places unnecessary. When login is used, the pam option
enables access control through pam(3PAM).


Authentication must be completed before IPCP (or other network protocol)
can be started. If the peer is required to authenticate itself and fails,
pppd closes LCP and terminates the link. If IPCP negotiates an
unacceptable IP address for the remote host, IPCP is closed. IP packets
are sent or received only when IPCP is open.


To allow hosts that cannot authenticate themselves to connect and use one
of a restricted set of IP addresses, add a line to the pap-secrets file
specifying the empty string for the client name and secret.


Additional pppd options for a given peer may be specified by placing them
at the end of the secrets entry, separated by two dashes (--). For
example

peername servername secret ip-address -- novj

Routing

When IPCP negotiation is complete, pppd informs the kernel of the local
and remote IP addresses for the PPP interface and creates a host route to
the remote end of the link that enables peers to exchange IP packets.
Communication with other machines generally requires further modification
to routing tables and/or Address Resolution Protocol (ARP) tables. In
most cases the defaultroute and/or proxyarp options are sufficient for
this, but further intervention may be necessary. If further intervention
is required, use the /etc/ppp/ip-up script or a routing protocol daemon.


To add a default route through the remote host, use the defaultroute
option. This option is typically used for "client" systems; that is, end-
nodes that use the PPP link for access to the general Internet.


In some cases it is desirable to use proxy ARP, for example on a server
machine connected to a LAN, to allow other hosts to communicate with the
remote host. proxyarp instructs pppd to look for a network interface on
the same subnet as the remote host. That is, an interface supporting
broadcast and ARP that is not a point-to-point or loopback interface and
that is currently up. 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.


When the demand option is used, the interface IP addresses are already
set at the time when IPCP comes up. If pppd cannot negotiate the same
addresses it used to configure the interface, it changes the interface IP
addresses to the negotiated addresses. This may disrupt existing
connections. Using demand dialing with peers that perform dynamic IP
address assignment is not recommended.

Scripts

pppd invokes scripts at various stages during processing that are used to
perform site-specific ancillary processing. These scripts may be shell
scripts or executable programs. 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), enabling them to update routing tables, run privileged
daemons, or perform other tasks. Be sure 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 pppd environment variables are:

DEVICE
Name of the serial tty device.


IFNAME
Name of the network interface.


IPLOCAL
IP address for the link's local end. This is set only when
IPCP has started.


IPREMOTE
IP address for the link's remote end. This is set only
when IPCP has started.


PEERNAME
Authenticated name of the peer. This is set only if the
peer authenticates itself.


SPEED
Baud rate of the tty device.


ORIG_UID
Real user-id of user who invoked pppd.


PPPLOGNAME
Username of the real user-id who invoked pppd. This is
always set.


pppd also sets the following variables for the ip-down and auth-down
scripts:

CONNECT_TIME
Number of seconds between the start of PPP negotiation
and connection termination.


BYTES_SENT
Number of bytes sent at the level of the serial port
during the connection.


BYTES_RCVD
Number of bytes received at the level of the serial port
during the connection.


LINKNAME
Logical name of the link, set with the linkname option.


If they exist, pppd invokes the following scripts. It is not an error if
they do not exist.

/etc/ppp/auth-up
Program or script executed after the remote system
successfully authenticates itself. It is executed
with five command-line arguments: interface-name
peer-name user-name tty-device speed. Note that
this script is not executed if the peer does not
authenticate itself, for example, when the noauth
option is used.


/etc/ppp/auth-down
Program or script executed when the link goes down
if /etc/ppp/auth-up was previously executed. It is
executed in the same manner with the same
parameters as /etc/ppp/auth-up.


/etc/ppp/ip-up
A program or script that is executed when the link
is available for sending and receiving IP packets
(that is, IPCP has come up). It is executed with six
command-line arguments: interface-name tty-device
speed local-IP-address remote-IP-address ipparam.


/etc/ppp/ip-down
A program or script which is executed when the link
is no longer available for sending and receiving IP
packets. This script can be used for undoing the
effects of the /etc/ppp/ip-up script. It is invoked
in the same manner and with the same parameters as
the ip-up script.


/etc/ppp/ipv6-up
Similar to /etc/ppp/ip-up, except that it is
executed when the link is available for sending and
receiving IPv6 packets. Executed with six command-
line arguments: interface-name tty-device speed
local-link-local-address remote-link-local-address
ipparam.


/etc/ppp/ipv6-down
Similar to /etc/ppp/ip-down, but executed when
IPv6 packets can no longer be transmitted on the
link. Executed with the same parameters as the
ipv6-up script.

EXAMPLES

Example 1: Using the auth Option

The following examples assume that the /etc/ppp/options file contains the
auth option.


pppd is commonly used to dial out to an ISP. You can do this using the
"pppd call isp" command where the /etc/ppp/peers/isp file is set up to
contain a line similar to the following:


cua/a 19200 crtscts connect '/usr/bin/chat -f /etc/ppp/chat-isp' noauth


For this example, chat(1M) is used to dial the ISP's modem and process
any login sequence required. The /etc/ppp/chat-isp file is used by chat
and could contain the following:


ABORT "NO CARRIER"
ABORT "NO DIALTONE"
ABORT "ERROR"
ABORT "NO ANSWER"
ABORT "BUSY"
ABORT "Username/Password Incorrect"
"" "at"
OK "at&f&d2&c1"
OK "atdt2468135"
"name:" "^Umyuserid"
"word:" "\qmypassword"
"ispts" "\q^Uppp"
"~-^Uppp-~"


See the chat(1M) man page for details of chat scripts.

Example 2: Using pppd with proxyarp

pppd can also 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 as shown in the
following example:


example% pppd proxyarp

Example 3: Providing a User with Access to PPP Facilities

To provide a user with access to the PPP facilities, allocate an IP
address for the user's machine, create an entry in /etc/ppp/pap-secrets
or /etc/ppp/chap-secrets. This enables the user's machine to authenticate
itself. For example, to enable user "Joe" using machine "joespc" to dial
in to machine "server" and use the IP address "joespc.my.net," add the
following entry to the /etc/ppp/pap-secrets or /etc/ppp/chap-secrets
files:


joespc server "joe's secret" joespc.my.net


Alternatively, you can create another username, for example "ppp," whose
login shell is /usr/bin/pppd and whose home directory is /etc/ppp. If you
run pppd this way, add the options to the /etc/ppp/.ppprc file.


If your serial connection is complex, it may be useful to escape such
control characters as XON (^Q) and XOFF (^S), using asyncmap a0000. If
the path includes a telnet, escape ^] (asyncmap 200a0000). If the path
includes a rlogin command, add escape ff option to the options, because
rlogin removes the window-size-change sequence [0xff, 0xff, 0x73, 0x73,
followed by any 8 bytes] from the stream.

EXIT STATUS

The pppd exit status indicates errors or specifies why a link was
terminated. Exit status values are:

0
pppd has detached or the connection was successfully established
and terminated at the peer's request.


1
An immediately fatal error occurred. For example, an essential
system call failed.


2
An error was detected in the options given. For example, two
mutually exclusive options were used, or /etc/ppp/options is
missing and the user is not root.


3
pppd is not setuid-root and the invoking user is not root.


4
The kernel does not support PPP. For example, the PPP kernel
driver is not included or cannot be loaded.


5
pppd terminated because it was sent a SIGINT, SIGTERM or SIGHUP
signal.


6
The serial port could not be locked.


7
The serial port could not be opened.


8
The connect script failed and returned a non-zero exit status.


9
The command specified as the argument to the pty option could not
be run.


10
The PPP negotiation failed because no network protocols were able
to run.


11
The peer system failed or refused to authenticate itself.


12
The link was established successfully, but terminated because it
was idle.


13
The link was established successfully, but terminated because the
connect time limit was reached.


14
Callback was negotiated and an incoming call should arrive
shortly.


15
The link was terminated because the peer is not responding to echo
requests.


16
The link was terminated by the modem hanging up.


17
The PPP negotiation failed because serial loopback was detected.


18
The init script failed because a non-zero exit status was
returned.


19
Authentication to the peer failed.

FILES

/var/run/spppn.pid
Process-ID for pppd process on PPP interface
unit n.


/var/run/ppp-name.pid
Process-ID for pppd process for logical link
name (see the linkname option).


/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, otherwise pppd will log a
warning.


/etc/ppp/chap-secrets
Names, secrets and IP addresses for all
forms of CHAP authentication. The
/etc/ppp/pap-secrets file should be owned by
root should not readable or writable by any
other user, otherwise, pppd will log a
warning.


/etc/ppp/options
System default options for pppd, read before
user default options or command-line
options.


$HOME/.ppprc
User default options, read before
/etc/ppp/options.ttyname.


/etc/ppp/options.ttyname
System default options for the serial port
in use; read after $HOME/.ppprc. The ttyname
component of this filename is formed when
the initial /dev/ is stripped from the port
name (if present), and slashes (if any) are
converted to dots.


/etc/ppp/peers
Directory with options files that 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.

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Evolving |
+--------------------+-----------------+

SEE ALSO

chat(1M), ifconfig(1M), crypt(3C), pam(3PAM), attributes(5)


Haskin, D., Allen, E. RFC 2472 - IP Version 6 Over PPP. Network Working
Group. December 1998.


Jacobson, V. RFC 1144, Compressing TCP/IP Headers for Low-Speed Serial
Links. Network Working Group. February, 1990


Lloyd, B., Simpson, W. RFC 1334, PPP Authentication Protocols. Network
Working Group. October 1992.


McGregor, G. RFC 1332, The PPP Internet Protocol Control Protocol (IPCP).
Network Working Group. May 1992.


Rivest, R. RFC 1321, The MD5 Message-Digest Algorithm. Network Working
Group. April 1992


Simpson, W. RFC 1661, The Point-to-Point Protocol (PPP). Network Working
Group. July 1994.


Simpson, W. RFC 1662, HDLC-like Framing . Network Working Group. July
1994.

NOTES

These signals affect pppd behavior:

SIGINT, SIGTERM
Terminate the link, restore the serial device
settings and exit.


SIGHUP
Terminate the link, restore the serial device
settings and close the serial device. If the persist
or demand option is specified, pppd attempts to
reopen the serial device and start another connection
after the holdoff period. Otherwise pppd exits. If
received during the holdoff period, SIGHUP causes
pppd to end the holdoff period immediately.


SIGUSR1
Toggles the state of the debug option and prints link
status information to the log.


SIGUSR2
Causes pppd to renegotiate compression. This is
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 an implementation.)

DIAGNOSTICS

Messages are sent to the syslog daemon using facility LOG_DAEMON. To see
error and debug messages, edit the /etc/syslog.conf file to direct the
messages to the desired output device or file, or use the updetach or
logfile options.


The debug option causes the contents of all LCP, PAP, CHAP or IPCP
control packets sent or received to be logged. This is useful if PPP
negotiation does not succeed or if authentication fails.


Debugging can also be enabled or disabled by sending a SIGUSR1 signal,
which acts as a toggle to the pppd process.


November 21, 2001 PPPD(1M)