NAME
pppd - Point-to-Point Protocol Daemon
SYNOPSIS
pppd [
options ]
DESCRIPTION
PPP is the protocol used for establishing internet links over dial-up modems,
DSL connections, and many other types of point-to-point links. The
pppd
daemon works together with the kernel PPP driver to establish and maintain a
PPP link with another system (called the
peer) and to negotiate
Internet Protocol (IP) addresses for each end of the link. Pppd can also
authenticate the peer and/or supply authentication information to the peer.
PPP can be used with other network protocols besides IP, but such use is
becoming increasingly rare.
FREQUENTLY USED OPTIONS
- ttyname
- Use the serial port called ttyname to communicate
with the peer. If ttyname does not begin with a slash (/), the
string "/dev/" is prepended to ttyname to form the name
of the device to open. If no device name is given, or if the name of the
terminal connected to the standard input is given, pppd will use that
terminal, and will not fork to put itself in the background. A value for
this option from a privileged source cannot be overridden by a
non-privileged user.
- speed
- An option that is a decimal number is taken as the desired
baud rate for the serial device. On systems such as 4.4BSD and NetBSD, any
speed can be specified. Other systems (e.g. Linux, SunOS) only support the
commonly-used baud rates.
- asyncmap map
- This option sets the Async-Control-Character-Map (ACCM) for
this end of the link. The ACCM is a set of 32 bits, one for each of the
ASCII control characters with values from 0 to 31, where a 1 bit indicates
that the corresponding control character should not be used in PPP packets
sent to this system. The map is encoded as a hexadecimal number (without a
leading 0x) where the least significant bit (00000001) represents
character 0 and the most significant bit (80000000) represents character
31. Pppd will ask the peer to send these characters as a 2-byte escape
sequence. If multiple asyncmap options are given, the values are
ORed together. If no asyncmap option is given, the default is zero,
so pppd will ask the peer not to escape any control characters. To escape
transmitted characters, use the escape option.
- auth
- Require the peer to authenticate itself before allowing
network packets to be sent or received. This option is the default if the
system has a default route. If neither this option nor the noauth
option is specified, pppd will only allow the peer to use IP addresses to
which the system does not already have a route.
- call name
- Read additional options from the file
/etc/ppp/peers/name. This file may contain privileged options, such
as noauth, even if pppd is not being run by root. The name
string may not begin with / or include .. as a pathname component. The
format of the options file is described below.
- connect script
- Usually there is something which needs to be done to
prepare the link before the PPP protocol can be started; for instance,
with a dial-up modem, commands need to be sent to the modem to dial the
appropriate phone number. This option specifies an command for pppd to
execute (by passing it to a shell) before attempting to start PPP
negotiation. The chat (8) program is often useful here, as it provides a
way to send arbitrary strings to a modem and respond to received
characters. A value for this option from a privileged source cannot be
overridden by a non-privileged user.
- crtscts
- Specifies that pppd should set the serial port to use
hardware flow control using the RTS and CTS signals in the RS-232
interface. If neither the crtscts, the nocrtscts, the
cdtrcts nor the nocdtrcts option is given, the hardware flow
control setting for the serial port is left unchanged. Some serial ports
(such as Macintosh serial ports) lack a true RTS output. Such serial ports
use this mode to implement unidirectional flow control. The serial port
will suspend transmission when requested by the modem (via CTS) but will
be unable to request the modem to stop sending to the computer. This mode
retains the ability to use DTR as a modem control line.
- 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 nodefaultroute option has been specified.
- disconnect script
- Execute the command specified by script, by passing
it to a shell, after pppd has terminated the link. This command could, for
example, issue commands to the modem to cause it to hang up if hardware
modem control signals were not available. The disconnect script is not run
if the modem has already hung up. A value for this option from a
privileged source cannot be overridden by a non-privileged user.
- escape 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 escape option, unlike the
asyncmap option which only allows control characters to be
specified. The characters which may not be escaped are those with hex
values 0x20 - 0x3f or 0x5e.
- file name
- Read options from file name (the format is described
below). The file must be readable by the user who has invoked pppd.
- init script
- Execute the command specified by script, by passing
it to a shell, to initialize the serial line. This script would typically
use the chat(8) program to configure the modem to enable auto answer. A
value for this option from a privileged source cannot be overridden by a
non-privileged user.
- lock
- Specifies that pppd should create a UUCP-style lock file
for the serial device to ensure exclusive access to the device. By
default, pppd will not create a lock file.
- mru n
- Set the MRU [Maximum Receive Unit] value to n. Pppd
will ask the peer to send packets of no more than n bytes. The
value of n must be between 128 and 16384; the default is 1500. A
value of 296 works well on very slow links (40 bytes for TCP/IP header +
256 bytes of data). Note that for the IPv6 protocol, the MRU must be at
least 1280.
- mtu n
- Set the MTU [Maximum Transmit Unit] value to n.
Unless the peer requests a smaller value via MRU negotiation, pppd will
request that the kernel networking code send data packets of no more than
n bytes through the PPP network interface. Note that for the IPv6
protocol, the MTU must be at least 1280.
- passive
- Enables the "passive" option in the LCP. With
this option, pppd will attempt to initiate a connection; if no reply is
received from the peer, pppd will then just wait passively for a valid LCP
packet from the peer, instead of exiting, as it would without this
option.
OPTIONS
- <local_IP_address>:<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 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, 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.
- +ipv6
- Enable the IPv6CP and IPv6 protocols.
- 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 (e.g. ::dead:beef). If the
ipv6cp-use-ipaddr option is given, the local identifier is the
local IPv4 address (see above). On systems which supports a unique
persistent id, such as EUI-48 derived from the Ethernet MAC address,
ipv6cp-use-persistent option can be used to replace the ipv6
<local>,<remote> option. Otherwise the identifier is
randomized.
- active-filter 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
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
filter-expression syntax is as described for tcpdump(1), except
that qualifiers which are inappropriate for a PPP link, such as
ether and 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
currently only available under Linux, and requires that the kernel was
configured to include PPP filtering support (CONFIG_PPP_FILTER). Note that
it is possible to apply different constraints to incoming and outgoing
packets using the inbound and outbound qualifiers.
- allow-ip address(es)
- Allow peers to use the given IP address or subnet without
authenticating themselves. The parameter is parsed as for each element of
the list of allowed IP addresses in the secrets files (see the
AUTHENTICATION section below).
- allow-number number
- Allow peers to connect from the given telephone number. A
trailing `*' character will match all numbers beginning with the leading
part.
- 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 give 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.
- cdtrcts
- Use a non-standard hardware flow control (i.e. DTR/CTS) to
control the flow of data on the serial port. If neither the
crtscts, the nocrtscts, the cdtrcts nor the
nocdtrcts option is given, the hardware flow control setting for
the serial port is left unchanged. Some serial ports (such as Macintosh
serial ports) lack a true RTS output. Such serial ports use this mode to
implement true bi-directional flow control. The sacrifice is that this
flow control mode does not permit using DTR as a modem control line.
- 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 (default 3).
- child-timeout n
- When exiting, wait for up to n seconds for any child
processes (such as the command specified with the pty command) to
exit before exiting. At the end of the timeout, pppd will send a SIGTERM
signal to any remaining child processes and exit. A value of 0 means no
timeout, that is, pppd will wait until all child processes have
exited.
- connect-delay n
- Wait for up to n milliseconds after the connect
script finishes for a valid PPP packet from the peer. At the end of this
time, or when a valid PPP packet is received from the peer, pppd will
commence negotiation by sending its first LCP packet. The default value is
1000 (1 second). This wait period only applies if the connect or
pty option is used.
- debug
- Enables connection debugging facilities. If this option is
given, pppd will log the contents of all control packets sent or received
in a readable form. The packets are logged through syslog with facility
daemon and level debug. This information can be directed to
a file by setting up /etc/syslog.conf appropriately (see
syslog.conf(5)).
- default-asyncmap
- Disable asyncmap negotiation, forcing all control
characters to be escaped for both the transmit and the receive
direction.
- default-mru
- Disable MRU [Maximum Receive Unit] negotiation. With this
option, pppd will use the default MRU value of 1500 bytes for both the
transmit and receive direction.
- deflate nr,nt
- 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. 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 give 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 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.)
- demand
- Initiate the link only on demand, i.e. when data traffic is
present. With this option, the remote IP address may be specified by the
user on the command line or in an options file, or if not, pppd will use
an arbitrary address in the 10.x.x.x range. Pppd will initially configure
the interface and enable it for IP traffic without connecting to the peer.
When traffic is available, pppd will connect to the peer and perform
negotiation, authentication, etc. When this is completed, pppd will
commence passing data packets (i.e., IP packets) across the link.
The demand option implies the persist option. If this
behaviour is not desired, use the nopersist option after the
demand option. The idle and holdoff options are also
useful 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. Pppd would then use the name
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.
- dryrun
- With the dryrun option, pppd will print out all the
option values which have been set and then exit, after parsing the command
line and options files and checking the option values, but before
initiating the link. The option values are logged at level info, and also
printed to standard output unless the device on standard output is the
device that pppd would be using to communicate with the peer.
- dump
- With the dump option, pppd will print out all the
option values which have been set. This option is like the dryrun
option except that pppd proceeds as normal rather than exiting.
- enable-session
- Enables session accounting via PAM or wtwp/wtmpx, as
appropriate. When PAM is enabled, the PAM "account" and
"session" module stacks determine behavior, and are enabled for
all PPP authentication protocols. When PAM is disabled, wtmp/wtmpx entries
are recorded regardless of whether the peer name identifies a valid user
on the local system, making peers visible in the last(1) log. This feature
is automatically enabled when the pppd login option is used.
Session accounting is disabled by default.
- endpoint <epdisc>
- Sets the endpoint discriminator sent by the local machine
to the peer during multilink negotiation to <epdisc>. The
default is to use the MAC address of the first ethernet interface on the
system, if any, otherwise the IPv4 address corresponding to the hostname,
if any, provided it is not in the multicast or locally-assigned IP address
ranges, or the localhost address. The endpoint discriminator can be the
string null or of the form type:value, where type is
a decimal number or one of the strings local, IP,
MAC, magic, or phone. The value is an IP address in
dotted-decimal notation for the IP type, or a string of bytes in
hexadecimal, separated by periods or colons for the other types. For the
MAC type, the value may also be the name of an ethernet or similar network
interface. This option is currently only available under Linux.
- eap-interval n
- If this option is given and pppd authenticates the peer
with EAP (i.e., is the server), pppd will restart EAP authentication every
n seconds. For EAP SRP-SHA1, see also the srp-interval
option, which enables lightweight rechallenge.
- eap-max-rreq n
- Set the maximum number of EAP Requests to which pppd will
respond (as a client) without hearing EAP Success or Failure. (Default is
20.)
- eap-max-sreq n
- Set the maximum number of EAP Requests that pppd will issue
(as a server) while attempting authentication. (Default is 10.)
- eap-restart n
- Set the retransmit timeout for EAP Requests when acting as
a server (authenticator). (Default is 3 seconds.)
- eap-timeout n
- Set the maximum time to wait for the peer to send an EAP
Request when acting as a client (authenticatee). (Default is 20
seconds.)
- 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 only has any effect if the
persist or demand option is used. The holdoff period is not
applied if the link was terminated because it was idle.
- idle n
- Specifies that pppd should 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. Note: it is not advisable to use this
option with the persist option without the demand option. If
the active-filter option is given, data packets which are rejected
by the specified activity filter also count as the link being idle.
- ipcp-accept-local
- With this option, pppd will accept the peer's idea of our
local IP address, even if the local IP address was specified in an
option.
- ipcp-accept-remote
- With this option, pppd will accept the peer's idea of its
(remote) IP address, even if the remote IP address was specified in an
option.
- 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 returned
before starting to send 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, ip-pre-up and
ip-down scripts. If this option is given, the string supplied is
given as the 6th parameter to those scripts.
- ipv6cp-accept-local
- With this option, pppd will accept the peer's idea of our
local IPv6 interface identifier, even if the local IPv6 interface
identifier was specified in an option.
- 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 returned
before starting to send 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).
- 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.
- ipx-network n
- Set the IPX network number in the IPXCP configure request
frame to n, 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.
- ipx-node n:m
- Set the IPX node numbers. The two node numbers are
separated from each other with a colon character. The first number
n is the local node number. The second number m 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.
- ipx-router-name <string>
- Set the name of the router. This is a string and is sent to
the peer as information data.
- ipx-routing n
- Set the routing protocol to be received by this option.
More than one instance of ipx-routing may be specified. The
'none' option (0) may be specified as the only instance of
ipx-routing. The values may be 0 for NONE, 2 for
RIP/SAP, and 4 for NLSP.
- 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.
- 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.
- 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.
- ipxcp-max-configure n
- Set the maximum number of IPXCP configure request frames
which the system will send to n. The default is 10.
- ipxcp-max-failure n
- Set the maximum number of IPXCP NAK frames which the local
system will send before it rejects the options. The default value is
3.
- ipxcp-max-terminate n
- Set the maximum number of IPXCP terminate request frames
before the local system considers that the peer is not listening to them.
The default value is 3.
- kdebug n
- Enable debugging code in the kernel-level PPP driver. The
argument values depend on the specific kernel driver, but in general a
value of 1 will enable general kernel debug messages. (Note that these
messages are usually only useful for debugging the kernel driver itself.)
For the Linux 2.2.x kernel driver, the value is a sum of bits: 1 to enable
general debug messages, 2 to request that the contents of received packets
be printed, and 4 to request that the contents of transmitted packets be
printed. On most systems, messages printed by the kernel are logged by
syslog(1) to a file as directed in the /etc/syslog.conf configuration
file.
- ktune
- Enables pppd to alter kernel settings as appropriate. Under
Linux, pppd will enable IP forwarding (i.e. set
/proc/sys/net/ipv4/ip_forward to 1) if the proxyarp option is used,
and will enable the dynamic IP address option (i.e. set
/proc/sys/net/ipv4/ip_dynaddr to 1) in demand mode if the local address
changes.
- lcp-echo-failure n
- If this option is given, pppd will presume the peer to be
dead if n LCP echo-requests are sent without receiving a valid LCP
echo-reply. If this happens, pppd will terminate the connection. Use of
this option requires a non-zero value for the lcp-echo-interval
parameter. This option can be used to enable pppd to terminate after the
physical connection has been broken (e.g., the modem has hung up) in
situations where no hardware modem control lines are available.
- lcp-echo-interval n
- If this option is given, pppd will send an LCP echo-request
frame to the peer every n seconds. Normally the peer should respond
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 returned
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 will
create a file named ppp-name.pid in /var/run (or
/etc/ppp on some systems) containing its process ID. This can be useful in
determining which instance of pppd is responsible for the link to a given
peer system. This is a privileged option.
- local
- Don't use the modem control lines. With this option, pppd
will ignore the state of the CD (Carrier Detect) signal from the modem and
will not change the state of the DTR (Data Terminal Ready) signal. This is
the opposite of the modem option.
- logfd n
- Send log messages to file descriptor n. Pppd will
send log messages to at most one file or file descriptor (as well as
sending the log messages to syslog), so this option and the logfile
option are mutually exclusive. The default is for pppd to send log
messages to stdout (file descriptor 1), unless the serial port is already
open on stdout.
- logfile filename
- Append log messages to the file filename (as well as
sending the log messages to syslog). The file is opened with the
privileges of the user who invoked pppd, in append mode.
- login
- Use the system password database for authenticating the
peer using PAP, and record the user in the system wtmp file. Note that the
peer must have an entry in the /etc/ppp/pap-secrets file as well as the
system password database to be allowed access. See also the
enable-session option.
- master_detach
- If multilink is enabled and this pppd process is the
multilink bundle master, and the link controlled by this pppd process
terminates, this pppd process continues to run in order to maintain the
bundle. If the master_detach option has been given, pppd will
detach from its controlling terminal in this situation, even if the
nodetach option has been given.
- maxconnect n
- Terminate the connection when it has been available for
network traffic for n seconds (i.e. n seconds after the
first network control protocol comes up).
- 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 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 crtscts option. This is the opposite of the local
option.
- mp
- Enables the use of PPP multilink; this is an alias for the
`multilink' option. This option is currently only available under
Linux.
- mppe-stateful
- Allow MPPE to use stateful mode. Stateless mode is still
attempted first. The default is to disallow stateful mode.
- mpshortseq
- Enables the use of short (12-bit) sequence numbers in
multilink headers, as opposed to 24-bit sequence numbers. This option is
only available under Linux, and only has any effect if multilink is
enabled (see the multilink option).
- mrru n
- Sets the Maximum Reconstructed Receive Unit to n.
The MRRU is the maximum size for a received packet on a multilink bundle,
and is analogous to the MRU for the individual links. This option is
currently only available under Linux, and only has any effect if multilink
is enabled (see the multilink option).
- 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. (This option was present in some
older versions of pppd under the name dns-addr.)
- ms-wins <addr>
- If pppd is acting as a server for Microsoft Windows or
"Samba" clients, this option allows pppd to supply one or two
WINS (Windows Internet Name Services) server addresses to the clients. The
first instance of this option specifies the primary WINS address; the
second instance (if given) specifies the secondary WINS address.
- multilink
- Enables the use of the PPP multilink protocol. If the peer
also supports multilink, then this link can become part of a bundle
between the local system and the peer. If there is an existing bundle to
the peer, pppd will join this link to that bundle, otherwise pppd will
create a new bundle. See the MULTILINK section below. This option is
currently only available under Linux.
- name name
- Set the name of the local system for authentication
purposes to name. This is a privileged option. With this option,
pppd will use lines in the secrets files which have name as the
second field when looking for a secret to use in authenticating the peer.
In addition, unless overridden with the user option, name
will be used as the name to send to the peer when authenticating the local
system to the peer. (Note that pppd does not append the domain name to
name.)
- noaccomp
- Disable 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.
- noccp
- Disable CCP (Compression Control Protocol) negotiation.
This option should only be required if the peer is buggy and gets confused
by requests from pppd for CCP negotiation.
- nocrtscts
- Disable hardware flow control (i.e. RTS/CTS) on the serial
port. If neither the crtscts nor the nocrtscts nor the
cdtrcts nor the nocdtrcts option is given, the hardware flow
control setting for the serial port is left unchanged.
- nocdtrcts
- This option is a synonym for nocrtscts. Either of
these options will disable both forms of hardware flow control.
- nodefaultroute
- Disable the defaultroute option. The system
administrator who wishes to prevent users from creating default routes
with pppd can do so by placing this option in the /etc/ppp/options
file.
- nodeflate
- Disables Deflate compression; pppd will not request or
agree to compress packets using the Deflate scheme.
- nodetach
- Don't detach from the controlling terminal. Without this
option, if a serial device other than the terminal on the standard input
is specified, pppd will fork to become a background process.
- noendpoint
- Disables pppd from sending an endpoint discriminator to the
peer or accepting one from the peer (see the MULTILINK section below).
This option should only be required if the peer is buggy.
- noip
- Disable IPCP negotiation and IP communication. This option
should only be required if the peer is buggy and gets confused by requests
from pppd for IPCP negotiation.
- noipv6
- Disable IPv6CP negotiation and IPv6 communication. This
option should only be required if the peer is buggy and gets confused by
requests from pppd for IPv6CP negotiation.
- 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).
- noipx
- Disable the IPXCP and IPX protocols. This option should
only be required if the peer is buggy and gets confused by requests from
pppd for IPXCP negotiation.
- noktune
- Opposite of the ktune option; disables pppd from
changing system settings.
- nolock
- Opposite of the lock option; specifies that pppd
should not create a UUCP-style lock file for the serial device. This
option is privileged.
- nolog
- Do not send log messages to a file or file descriptor. This
option cancels the logfd and logfile options.
- nomagic
- Disable magic number negotiation. With this option, pppd
cannot detect a looped-back line. This option should only be needed if the
peer is buggy.
- nomp
- Disables the use of PPP multilink. This option is currently
only available under Linux.
- nomppe
- Disables MPPE (Microsoft Point to Point Encryption). This
is the default.
- nomppe-40
- Disable 40-bit encryption with MPPE.
- nomppe-128
- Disable 128-bit encryption with MPPE.
- nomppe-stateful
- Disable MPPE stateful mode. This is the default.
- nompshortseq
- Disables the use of short (12-bit) sequence numbers in the
PPP multilink protocol, forcing the use of 24-bit sequence numbers. This
option is currently only available under Linux, and only has any effect if
multilink is enabled.
- nomultilink
- Disables the use of PPP multilink. This option is currently
only available under Linux.
- nopcomp
- Disable protocol field compression negotiation in both 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 has been
specified.
- nopredictor1
- Do not accept or agree to Predictor-1 compression.
- noproxyarp
- Disable the proxyarp option. The system
administrator who wishes to prevent users from creating proxy ARP entries
with pppd can do so by placing this option in the /etc/ppp/options
file.
- noremoteip
- Allow pppd to operate without having an IP address for the
peer. This option is only available under Linux. Normally, pppd will
request the peer's IP address, and if the peer does not supply it, pppd
will use an arbitrary address in the 10.x.x.x subnet. With this option, if
the peer does not supply its IP address, pppd will not ask the peer for
it, and will not set the destination address of the ppp interface. In this
situation, the ppp interface can be used for routing by creating device
routes, but the peer itself cannot be addressed directly for IP
traffic.
- notty
- Normally, pppd requires a terminal device. With this
option, pppd will allocate itself a pseudo-tty master/slave pair and use
the slave as its terminal device. Pppd will create a child process to act
as a `character shunt' to transfer characters between the pseudo-tty
master and its standard input and output. Thus pppd will transmit
characters on its standard output and receive characters on its standard
input even if they are not terminal devices. This option increases the
latency and CPU overhead of transferring data over the ppp interface as
all of the characters sent and received must flow through the character
shunt process. An explicit device name may not be given if this option is
used.
- 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 will not
omit the connection-ID byte from Van Jacobson compressed TCP/IP headers,
nor ask the peer to do so.
- papcrypt
- Indicates that all secrets in the /etc/ppp/pap-secrets file
which are used for checking the identity of the peer are encrypted, and
thus pppd should not accept a password which, before encryption, is
identical to the secret from the /etc/ppp/pap-secrets file.
- 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 will wait for the peer to
authenticate itself with PAP to n seconds (0 means no limit).
- pass-filter 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 very basic firewall capability.
The filter-expression syntax is as described for tcpdump(1), except
that qualifiers which are inappropriate for a PPP link, such as
ether and 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 inbound and outbound qualifiers. This option is
currently only available under Linux, and requires that the kernel was
configured to include PPP filtering support (CONFIG_PPP_FILTER).
- password password-string
- Specifies the password to use for authenticating to the
peer. Use of this option is discouraged, as the password is likely to be
visible to other users on the system (for example, by using ps(1)).
- persist
- Do not exit after a connection is terminated; instead try
to reopen the connection. The maxfail option still has an effect on
persistent connections.
- plugin filename
- Load the shared library object file filename as a
plugin. This is a privileged option. If filename does not contain a
slash (/), pppd will look in the /usr/lib/pppd/version
directory for the plugin, where version is the version number of
pppd (for example, 2.4.2).
- 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.
- privgroup group-name
- Allows members of group group-name to use privileged
options. This is a privileged option. Use of this option requires care as
there is no guarantee that members of group-name cannot use pppd to
become root themselves. Consider it equivalent to putting the members of
group-name in the kmem or disk group.
- proxyarp
- Add an entry to this system's ARP [Address Resolution
Protocol] table with the IP address of the peer and the Ethernet address
of this system. This will have the effect of making the peer appear to
other systems to be on the local ethernet.
- pty script
- Specifies that the command script is to be used to
communicate rather than a specific terminal device. Pppd will allocate
itself a pseudo-tty master/slave pair and use the slave as its terminal
device. The script will be run in a child process with the
pseudo-tty master as its standard input and output. An explicit device
name may not be given if this option is used. (Note: if the 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 will accept all control characters
from the peer, including those marked in the receive asyncmap. Without
this option, pppd will discard those characters as specified in RFC1662.
This option should only be needed if the peer is buggy.
- record filename
- Specifies that pppd should record all characters sent and
received to a file named filename. This file is opened in append
mode, using the user's user-ID and permissions. This option is implemented
using a pseudo-tty and a process to transfer characters between the
pseudo-tty and the real serial device, so it will increase the latency and
CPU overhead of transferring data over the ppp interface. The characters
are stored in a tagged format with timestamps, which can be displayed in
readable form using the pppdump(8) program.
- remotename name
- Set the assumed name of the remote system for
authentication purposes to name.
- remotenumber number
- Set the assumed telephone number of the remote system for
authentication purposes to number.
- refuse-chap
- With this option, pppd will not agree to authenticate
itself to the peer using CHAP.
- refuse-mschap
- With this option, pppd will not agree to authenticate
itself to the peer using MS-CHAP.
- refuse-mschap-v2
- With this option, pppd will not agree to authenticate
itself to the peer using MS-CHAPv2.
- refuse-eap
- With this option, pppd will not agree to authenticate
itself to the peer using EAP.
- refuse-pap
- With this option, pppd will not agree to authenticate
itself to the peer using PAP.
- require-chap
- Require the peer to authenticate itself using CHAP
[Challenge Handshake Authentication Protocol] authentication.
- require-mppe
- Require the use of MPPE (Microsoft Point to Point
Encryption). This option disables all other compression types. This option
enables both 40-bit and 128-bit encryption. In order for MPPE to
successfully come up, you must have authenticated with either MS-CHAP or
MS-CHAPv2. This option is presently only supported under Linux, and only
if your kernel has been configured to include MPPE support.
- require-mppe-40
- Require the use of MPPE, with 40-bit encryption.
- require-mppe-128
- Require the use of MPPE, with 128-bit encryption.
- require-mschap
- Require the peer to authenticate itself using MS-CHAP
[Microsoft Challenge Handshake Authentication Protocol]
authentication.
- require-mschap-v2
- Require the peer to authenticate itself using MS-CHAPv2
[Microsoft Challenge Handshake Authentication Protocol, Version 2]
authentication.
- require-eap
- Require the peer to authenticate itself using EAP
[Extensible Authentication Protocol] authentication.
- require-pap
- Require the peer to authenticate itself using PAP [Password
Authentication Protocol] authentication.
- set name=value
- Set an environment variable for scripts that are invoked by
pppd. When set by a privileged source, the variable specified by
name cannot be changed by options contained in an unprivileged
source. See also the unset option and the environment described in
SCRIPTS.
- show-password
- When logging the 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
(as for the `passive' option with ancient versions of pppd).
- srp-interval n
- If this parameter is given and pppd uses EAP SRP-SHA1 to
authenticate the peer (i.e., is the server), then pppd will use the
optional lightweight SRP rechallenge mechanism at intervals of n
seconds. This option is faster than eap-interval reauthentication
because it uses a hash-based mechanism and does not derive a new session
key.
- srp-pn-secret string
- Set the long-term pseudonym-generating secret for the
server. This value is optional and if set, needs to be known at the server
(authenticator) side only, and should be different for each server (or
poll of identical servers). It is used along with the current date to
generate a key to encrypt and decrypt the client's identity contained in
the pseudonym.
- srp-use-pseudonym
- When operating as an EAP SRP-SHA1 client, attempt to use
the pseudonym stored in ~/.ppp_pseudonym first as the identity, and save
in this file any pseudonym offered by the peer during authentication.
- sync
- Use synchronous HDLC serial encoding instead of
asynchronous. The device used by pppd with this option must have sync
support. Currently supports Microgate SyncLink adapters under Linux and
FreeBSD 2.2.8 and later.
- unit num
- Sets the ppp unit number (for a ppp0 or ppp1 etc interface
name) for outbound connections.
- unset name
- Remove a variable from the environment variable for scripts
that are invoked by pppd. When specified by a privileged source, the
variable name cannot be set by options contained in an unprivileged
source. See also the set option and the environment described in
SCRIPTS.
- updetach
- With this option, pppd will detach from its controlling
terminal once it has successfully established the ppp connection (to the
point where the first network control protocol, usually the IP control
protocol, has come up).
- 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 name option). This option is not normally needed
since the name option is privileged.
- usepeerdns
- Ask the peer for up to 2 DNS server addresses. The
addresses supplied by the peer (if any) are passed to the /etc/ppp/ip-up
script in the environment variables DNS1 and DNS2, and the environment
variable USEPEERDNS will be set to 1. In addition, pppd will create an
/etc/ppp/resolv.conf file containing one or two nameserver lines with the
address(es) supplied by the peer.
- 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 (i.e. XON/XOFF) to control the
flow of data on the serial port.
OPTIONS FILES
Options can be taken from files as well as the command line. Pppd reads options
from the files /etc/ppp/options, ~/.ppprc and /etc/ppp/options.
ttyname
(in that order) before processing the options on the command line. (In fact,
the command-line options are scanned to find the terminal name before the
options.
ttyname file is read.) In forming the name of the options.
ttyname file, the initial /dev/ is removed from the terminal name, and
any remaining / characters are replaced with dots.
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
file or
call options within an options file.
SECURITY
pppd provides system administrators with sufficient access control that
PPP access to a server machine can be provided to legitimate users without
fear of compromising the security of the server or the network it's on. This
control is provided through restrictions on which IP addresses the peer may
use, based on its authenticated identity (if any), and through restrictions on
which options a non-privileged user may use. Several of pppd's options are
privileged, in particular those which permit potentially insecure
configurations; these options are only accepted in files which are under the
control of the system administrator, or if pppd is being run by root.
The default behaviour of pppd is to allow an unauthenticated peer to use a given
IP address only if the system does not already have a route to that IP
address. For example, a system with a permanent connection to the wider
internet will normally have a default route, and thus all peers will have to
authenticate themselves in order to set up a connection. On such a system, the
auth option is the default. On the other hand, a system where the PPP
link is the only connection to the internet will not normally have a default
route, so the peer will be able to use almost any IP address without
authenticating itself.
As indicated above, some security-sensitive options are privileged, which means
that they may not be used by an ordinary non-privileged user running a
setuid-root pppd, either on the command line, in the user's ~/.ppprc file, or
in an options file read using the
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 being run by the root user, privileged options
can be used without restriction.
When opening the device, pppd uses either the invoking user's user ID or the
root UID (that is, 0), depending on whether the device name was specified by
the user or the system administrator. If the device name comes from a
privileged source, that is, /etc/ppp/options or an options file read using the
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 which
they would not normally have permission to access. Otherwise pppd uses the
invoking user's real UID when opening the device.
AUTHENTICATION
Authentication is the process whereby one peer convinces the other of its
identity. This involves the first peer sending its name to the other, together
with some kind of secret information which could only come from the genuine
authorized user of that name. In such an exchange, we will call the first peer
the "client" and the other the "server". The client has a
name by which it identifies itself to the server, and the server also has a
name by which it identifies itself to the client. Generally the genuine client
shares some secret (or password) with the server, and authenticates itself by
proving that it knows that secret. Very often, the names used for
authentication correspond to the internet hostnames of the peers, but this is
not essential.
At present, pppd supports three authentication protocols: the Password
Authentication Protocol (PAP), Challenge Handshake Authentication Protocol
(CHAP), and Extensible Authentication Protocol (EAP). PAP involves the client
sending its name and a cleartext password to the server to authenticate
itself. In contrast, the server initiates the CHAP authentication exchange by
sending a challenge to the client (the challenge packet includes the server's
name). The client must respond with a response which includes its name plus a
hash value derived from the shared secret and the challenge, in order to prove
that it knows the secret. EAP supports CHAP-style authentication, and also
includes the SRP-SHA1 mechanism, which is resistant to dictionary-based
attacks and does not require a cleartext password on the server side.
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.
The default behaviour of pppd is to agree to authenticate if requested, and to
not require authentication from the peer. However, pppd will not agree to
authenticate itself with a particular protocol if it has no secrets which
could be used to do so.
Pppd stores secrets for use in authentication in secrets files
(/etc/ppp/pap-secrets for PAP, /etc/ppp/chap-secrets for CHAP, MS-CHAP,
MS-CHAPv2, and EAP MD5-Challenge, and /etc/ppp/srp-secrets for EAP SRP-SHA1).
All secrets files have the same format. The secrets files can contain secrets
for pppd to use in authenticating itself to other systems, as well as secrets
for pppd to use when authenticating other systems to itself.
Each line in a secrets file contains one secret. A given secret is specific to a
particular combination of client and server - it can only be used by that
client to authenticate itself to that server. Thus each line in a secrets file
has at least 3 fields: the name of the client, the name of the server, and the
secret. These fields may be followed by a list of the IP addresses that the
specified client may use when connecting to the specified server.
A secrets file is parsed into words as for a options file, so the client name,
server name and secrets fields must each be one word, with any embedded spaces
or other special characters quoted or escaped. Note that case is significant
in the client and server names and in the secret.
If the secret starts with an `@', what follows is assumed to be the name of a
file from which to read the secret. A "*" as the client or server
name matches any name. When selecting a secret, pppd takes the best match,
i.e. the match with the fewest wildcards.
Any following words on the same line are taken to be a list of acceptable IP
addresses for that client. If there are only 3 words on the line, or if the
first word is "-", then all IP addresses are disallowed. To allow
any address, use "*". A word starting with "!" indicates
that the specified address is
not acceptable. An address may be
followed by "/" and a number
n, to indicate a whole subnet,
i.e. all addresses which 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 will be set to the unit number plus one.
Thus a secrets file contains both secrets for use in authenticating other hosts,
plus secrets which we use for authenticating ourselves to others. When pppd is
authenticating the peer (checking the peer's identity), it chooses a secret
with the peer's name in the first field and the name of the local system in
the second field. The name of the local system defaults to the hostname, with
the domain name appended if the
domain option is used. This default can
be overridden with the
name option, except when the
usehostname
option is used. (For EAP SRP-SHA1, see the srp-entry(8) utility for generating
proper validator entries to be used in the "secret" field.)
When pppd is choosing a secret to use in authenticating itself to the peer, it
first determines what name it is going to use to identify itself to the peer.
This name can be specified by the user with the
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 pppd looks for a
secret with this name in the first field and the peer's name in the second
field. Pppd will know the name of the peer if CHAP or EAP authentication is
being used, because the peer will have sent it in the challenge packet.
However, if PAP is being used, pppd will have to determine the peer's name
from the options specified by the user. The user can specify the peer's name
directly with the
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, pppd will use the null string as the
peer's name.
When authenticating the peer with PAP, the supplied password is first compared
with the secret from the secrets file. If the password doesn't match the
secret, the password is encrypted using crypt() and checked against the secret
again. Thus secrets for authenticating the peer can be stored in encrypted
form if desired. If the
papcrypt option is given, the first
(unencrypted) comparison is omitted, for better security.
Furthermore, if the
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
login option, the secret in
/etc/ppp/pap-secrets would be "", which will match any password
supplied by the peer. This avoids the need to have the same secret in two
places.
Authentication must be satisfactorily completed before IPCP (or any other
Network Control Protocol) can be started. If the peer is required to
authenticate itself, and fails to do so, pppd will terminated the link (by
closing LCP). If IPCP negotiates an unacceptable IP address for the remote
host, IPCP will be closed. IP packets can only be sent or received when IPCP
is open.
In some cases it is desirable to allow some hosts which can't authenticate
themselves to connect and use one of a restricted set of IP addresses, even
when the local host generally requires authentication. If the peer refuses to
authenticate itself when requested, pppd takes that as equivalent to
authenticating with PAP using the empty string for the username and password.
Thus, by adding a line to the pap-secrets file which specifies the empty
string for the client and password, it is possible to allow restricted access
to hosts which refuse to authenticate themselves.
ROUTING
When IPCP negotiation is completed successfully, pppd will inform the kernel of
the local and remote IP addresses for the ppp interface. This is sufficient to
create a host route to the remote end of the link, which will enable the peers
to exchange IP packets. Communication with other machines generally requires
further modification to routing tables and/or ARP (Address Resolution
Protocol) tables. In most cases the
defaultroute and/or
proxyarp
options are sufficient for this, but in some cases further intervention is
required. The /etc/ppp/ip-up script can be used for this.
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
defaultroute option causes pppd to create such a default
route when IPCP comes up, and delete it when the link is terminated.
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
proxyarp option causes pppd to look for a network
interface on the same subnet as the remote host (an interface supporting
broadcast and ARP, which is up and not a point-to-point or loopback
interface). If found, pppd creates a permanent, published ARP entry with the
IP address of the remote host and the hardware address of the network
interface found.
When the
demand option is used, the interface IP addresses have already
been set at the point when IPCP comes up. If pppd has not been able to
negotiate the same addresses that it used to configure the interface (for
example when the peer is an ISP that uses dynamic IP address assignment), pppd
has to change the interface IP addresses to the negotiated addresses. This may
disrupt existing connections, and the use of demand dialling with peers that
do dynamic IP address assignment is not recommended.
MULTILINK
Multilink PPP provides the capability to combine two or more PPP links between a
pair of machines into a single `bundle', which appears as a single virtual PPP
link which has the combined bandwidth of the individual links. Currently,
multilink PPP is only supported under Linux.
Pppd detects that the link it is controlling is connected to the same peer as
another link using the peer's endpoint discriminator and the authenticated
identity of the peer (if it authenticates itself). The endpoint discriminator
is a block of data which is hopefully unique for each peer. Several types of
data can be used, including locally-assigned strings of bytes, IP addresses,
MAC addresses, randomly strings of bytes, or E-164 phone numbers. The endpoint
discriminator sent to the peer by pppd can be set using the endpoint option.
In some circumstances the peer may send no endpoint discriminator or a
non-unique value. The bundle option adds an extra string which is added to the
peer's endpoint discriminator and authenticated identity when matching up
links to be joined together in a bundle. The bundle option can also be used to
allow the establishment of multiple bundles between the local system and the
peer. Pppd uses a TDB database in /var/run/pppd2.tdb to match up links.
Assuming that multilink is enabled and the peer is willing to negotiate
multilink, then when pppd is invoked to bring up the first link to the peer,
it will detect that no other link is connected to the peer and create a new
bundle, that is, another ppp network interface unit. When another pppd is
invoked to bring up another link to the peer, it will detect the existing
bundle and join its link to it.
If the first link terminates (for example, because of a hangup or a received LCP
terminate-request) the bundle is not destroyed unless there are no other links
remaining in the bundle. Rather than exiting, the first pppd keeps running
after its link terminates, until all the links in the bundle have terminated.
If the first pppd receives a SIGTERM or SIGINT signal, it will destroy the
bundle and send a SIGHUP to the pppd processes for each of the links in the
bundle. If the first pppd receives a SIGHUP signal, it will terminate its link
but not the bundle.
Note: demand mode is not currently supported with multilink.
EXAMPLES
The following examples assume that the /etc/ppp/options file contains the
auth option (as in the default /etc/ppp/options file in the ppp
distribution).
Probably the most common use of pppd is to dial out to an ISP. This can be done
with a command such as
- pppd call isp
where the /etc/ppp/peers/isp file is set up by the system administrator to
contain something like this:
- ttyS0 19200 crtscts
connect '/usr/sbin/chat -v -f /etc/ppp/chat-isp'
noauth
In this example, we are using chat to dial the ISP's modem and go through any
logon sequence required. The /etc/ppp/chat-isp file contains the script used
by chat; it could for example contain something like this:
- 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-~"
See the chat(8) man page for details of chat scripts.
Pppd can also be used to provide a dial-in ppp service for users. If the users
already have login accounts, the simplest way to set up the ppp service is to
let the users log in to their accounts and run pppd (installed setuid-root)
with a command such as
- pppd proxyarp
To allow a user to use the PPP facilities, you need to allocate an IP address
for that user's machine and create an entry in /etc/ppp/pap-secrets,
/etc/ppp/chap-secrets, or /etc/ppp/srp-secrets (depending on which
authentication method the PPP implementation on the user's machine supports),
so that the user's machine can authenticate itself. For example, if Joe has a
machine called "joespc" that is to be allowed to dial in to the
machine called "server" and use the IP address joespc.my.net, you
would add an entry like this to /etc/ppp/pap-secrets or /etc/ppp/chap-secrets:
- joespc server "joe's secret" joespc.my.net
(See srp-entry(8) for a means to generate the server's entry when SRP-SHA1 is in
use.) Alternatively, you can create a username called (for example)
"ppp", whose login shell is pppd and whose home directory is
/etc/ppp. Options to be used when pppd is run this way can be put in
/etc/ppp/.ppprc.
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
asyncmap a0000.
If the path includes a telnet, you probably should escape ^] as well (
asyncmap 200a0000). If the path includes an rlogin, you will need to
use the
escape 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.
DIAGNOSTICS
Messages are sent to the syslog daemon using facility LOG_DAEMON. (This can be
overridden by recompiling pppd with the macro LOG_PPP defined as the desired
facility.) See the syslog(8) documentation for details of where the syslog
daemon will write the messages. On most systems, the syslog daemon uses the
/etc/syslog.conf file to specify the destination(s) for syslog messages. You
may need to edit that file to suit.
The
debug option causes the contents of all control packets sent or
received to be logged, that is, all LCP, PAP, CHAP, EAP, or IPCP packets. This
can be useful if the PPP negotiation does not succeed or if authentication
fails. If debugging is enabled at compile time, the
debug option also
causes other debugging messages to be logged.
Debugging can also be enabled or disabled by sending a SIGUSR1 signal to the
pppd process. This signal acts as a toggle.
EXIT STATUS
The exit status of pppd is set to indicate whether any error was detected, or
the reason for the link being terminated. The values used are:
- 0
- Pppd has detached, or otherwise the connection was
successfully established and terminated at the peer's request.
- 1
- An immediately fatal error of some kind occurred, such as
an essential system call failing, or running out of virtual memory.
- 2
- An error was detected in processing the options given, such
as two mutually exclusive options being used.
- 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 (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, that is, it didn't reach the
point where at least one network protocol (e.g. IP) was running.
- 11
- The peer system failed (or refused) to authenticate
itself.
- 12
- The link was established successfully and terminated
because it was idle.
- 13
- The link was established successfully and 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 (returned a non-zero exit
status).
- 19
- We failed to authenticate ourselves to the peer.
SCRIPTS
Pppd invokes scripts at various stages in its processing which can be used to
perform site-specific ancillary processing. These scripts are usually shell
scripts, but could be executable code files instead. Pppd does not wait for
the scripts to finish (except for the ip-pre-up script). The scripts are
executed as root (with the real and effective user-id set to 0), so that they
can do things such as update routing tables or run privileged daemons. Be
careful that the contents of these scripts do not compromise your system's
security. Pppd runs the scripts with standard input, output and error
redirected to /dev/null, and with an environment that is empty except for some
environment variables that give information about the link. The environment
variables that pppd sets are:
- DEVICE
- The name of the serial tty device being used.
- IFNAME
- The name of the network interface being used.
- IPLOCAL
- The IP address for the local end of the link. This is only
set when IPCP has come up.
- IPREMOTE
- The IP address for the remote end of the link. This is only
set when IPCP has come up.
- PEERNAME
- The authenticated name of the peer. This is only set if the
peer authenticates itself.
- SPEED
- The baud rate of the tty device.
- ORIG_UID
- The real user-id of the user who invoked pppd.
- PPPLOGNAME
- The username of the real user-id that invoked pppd. This is
always set.
For the ip-down and auth-down scripts, pppd also sets the following variables
giving statistics for the connection:
- CONNECT_TIME
- The number of seconds from when the PPP negotiation started
until the connection was terminated.
- BYTES_SENT
- The number of bytes sent (at the level of the serial port)
during the connection.
- BYTES_RCVD
- The number of bytes received (at the level of the serial
port) during the connection.
- LINKNAME
- The logical name of the link, set with the linkname
option.
- DNS1
- If the peer supplies DNS server addresses, this variable is
set to the first DNS server address supplied (whether or not the
usepeerdns option was given).
- DNS2
- If the peer supplies DNS server addresses, this variable is
set to the second DNS server address supplied (whether or not the
usepeerdns option was given).
Pppd invokes the following scripts, if they exist. It is not an error if they
don't exist.
- /etc/ppp/auth-up
- A program or script which is executed after the remote
system successfully authenticates itself. It is executed with the
parameters
- interface-name peer-name user-name tty-device
speed
- Note that this script is not executed if the peer doesn't
authenticate itself, for example when the noauth option is
used.
- /etc/ppp/auth-down
- A program or script which is executed when the link goes
down, if /etc/ppp/auth-up was previously executed. It is executed in the
same manner with the same parameters as /etc/ppp/auth-up.
- /etc/ppp/ip-pre-up
- A program or script which is executed just before the ppp
network interface is brought up. It is executed with the same parameters
as the ip-up script (below). At this point the interface exists and has IP
addresses assigned but is still down. This can be used to add firewall
rules before any IP traffic can pass through the interface. Pppd will wait
for this script to finish before bringing the interface up, so this script
should run quickly.
- /etc/ppp/ip-up
- A program or script which is executed when the link is
available for sending and receiving IP packets (that is, IPCP has come
up). It is executed with the parameters
- 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 and /etc/ppp/ip-pre-up
scripts. It is invoked in the same manner and with the same parameters as
the ip-up script.
- /etc/ppp/ipv6-up
- Like /etc/ppp/ip-up, except that it is executed when the
link is available for sending and receiving IPv6 packets. It is executed
with the parameters
- 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 it is executed when IPv6
packets can no longer be transmitted on the link. It is executed with the
same parameters as the ipv6-up script.
- /etc/ppp/ipx-up
- A program or script which is executed when the link is
available for sending and receiving IPX packets (that is, IPXCP has come
up). It is executed with the parameters
- interface-name tty-device speed network-number
local-IPX-node-address remote-IPX-node-address
local-IPX-routing-protocol remote-IPX-routing-protocol
local-IPX-router-name remote-IPX-router-name ipparam pppd-pid
- The local-IPX-routing-protocol and
remote-IPX-routing-protocol field may be one of the following:
- NONE to indicate that there is no routing protocol
RIP to indicate that RIP/SAP should be used
NLSP to indicate that Novell NLSP should be used
RIP NLSP to indicate that both RIP/SAP and NLSP should be used
- /etc/ppp/ipx-down
- A program or script which is executed when the link is no
longer available for sending and receiving IPX packets. This script can be
used for undoing the effects of the /etc/ppp/ipx-up script. It is invoked
in the same manner and with the same parameters as the ipx-up script.
FILES
- /var/run/pppn.pid (BSD or Linux),
/etc/ppp/ppp n.pid (others)
- Process-ID for pppd process on ppp interface unit
n.
- /var/run/ppp-name.pid (BSD or
Linux),
- /etc/ppp/ppp-name.pid (others)
Process-ID for pppd process for logical link name (see the
linkname option).
- /var/run/pppd2.tdb
- Database containing information about pppd processes,
interfaces and links, used for matching links to bundles in multilink
operation. May be examined by external programs to obtain information
about running pppd instances, the interfaces and devices they are using,
IP address assignments, etc. /etc/ppp/pap-secrets Usernames,
passwords and IP addresses for PAP authentication. This file should be
owned by root and not readable or writable by any other user. Pppd will
log a warning if this is not the case.
- /etc/ppp/chap-secrets
- Names, secrets and IP addresses for CHAP/MS-CHAP/MS-CHAPv2
authentication. As for /etc/ppp/pap-secrets, this file should be owned by
root and not readable or writable by any other user. Pppd will log a
warning if this is not the case.
- /etc/ppp/srp-secrets
- Names, secrets, and IP addresses for EAP authentication. As
for /etc/ppp/pap-secrets, this file should be owned by root and not
readable or writable by any other user. Pppd will log a warning if this is
not the case.
- ~/.ppp_pseudonym
- Saved client-side SRP-SHA1 pseudonym. See the
srp-use-pseudonym option for details.
- /etc/ppp/options
- System default options for pppd, read before user default
options or command-line options.
- ~/.ppprc
- User default options, read before
/etc/ppp/options.ttyname.
- /etc/ppp/options.ttyname
- System default options for the serial port being used, read
after ~/.ppprc. In forming the ttyname part of this filename, an
initial /dev/ is stripped from the port name (if present), and any slashes
in the remaining part are converted to dots.
- /etc/ppp/peers
- A directory containing options files which may contain
privileged options, even if pppd was invoked by a user other than root.
The system administrator can create options files in this directory to
permit non-privileged users to dial out without requiring the peer to
authenticate, but only to certain trusted peers.
SEE ALSO
chat(8),
pppstats(8)
- RFC1144
- Jacobson, V. Compressing TCP/IP headers for low-speed
serial links. February 1990.
- RFC1321
- Rivest, R. The MD5 Message-Digest Algorithm. April
1992.
- RFC1332
- McGregor, G. PPP Internet Protocol Control Protocol
(IPCP). May 1992.
- RFC1334
- Lloyd, B.; Simpson, W.A. PPP authentication
protocols. October 1992.
- RFC1661
- Simpson, W.A. The Point-to-Point Protocol (PPP).
July 1994.
- RFC1662
- Simpson, W.A. PPP in HDLC-like Framing. July
1994.
- RFC2284
- Blunk, L.; Vollbrecht, J., PPP Extensible Authentication
Protocol (EAP). March 1998.
- RFC2472
- Haskin, D. IP Version 6 over PPP December 1998.
- RFC2945
- Wu, T., The SRP Authentication and Key Exchange
System September 2000.
- draft-ietf-pppext-eap-srp-03.txt
- Carlson, J.; et al., EAP SRP-SHA1 Authentication
Protocol. July 2001.
NOTES
Some limited degree of control can be exercised over a running pppd process by
sending it a signal from the list below.
- SIGINT, SIGTERM
- These signals cause pppd to terminate the link (by closing
LCP), restore the serial device settings, and exit. If a connector or
disconnector process is currently running, pppd will send the same signal
to its process group, so as to terminate the connector or disconnector
process.
- SIGHUP
- This signal causes pppd to terminate the link, restore the
serial device settings, and close the serial device. If the persist
or demand option has been specified, pppd will try to reopen the
serial device and start another connection (after the holdoff period).
Otherwise pppd will exit. If this signal is received during the holdoff
period, it causes pppd to end the holdoff period immediately. If a
connector or disconnector process is running, pppd will send the same
signal to its process group.
- SIGUSR1
- This signal toggles the state of the debug
option.
- SIGUSR2
- This signal causes pppd to renegotiate compression. This
can be useful to re-enable compression after it has been disabled as a
result of a fatal decompression error. (Fatal decompression errors
generally indicate a bug in one or other implementation.)
AUTHORS
Paul Mackerras (paulus@samba.org), based on earlier work by Drew Perkins, Brad
Clements, Karl Fox, Greg Christy, and Brad Parker.
COPYRIGHT
Pppd is copyrighted and made available under conditions which provide that it
may be copied and used in source or binary forms provided that the conditions
listed below are met. Portions of pppd are covered by the following copyright
notices:
Copyright (c) 1984-2000 Carnegie Mellon University. All rights reserved.
Copyright (c) 1993-2004 Paul Mackerras. All rights reserved.
Copyright (c) 1995 Pedro Roque Marques. All rights reserved.
Copyright (c) 1995 Eric Rosenquist. All rights reserved.
Copyright (c) 1999 Tommi Komulainen. All rights reserved.
Copyright (C) Andrew Tridgell 1999
Copyright (c) 2000 by Sun Microsystems, Inc. All rights reserved.
Copyright (c) 2001 by Sun Microsystems, Inc. All rights reserved.
Copyright (c) 2002 Google, Inc. All rights reserved.
The copyright notices contain the following statements.
Redistribution and use in source and binary forms, with or without modification,
are permitted provided that the following conditions are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
3. The name "Carnegie Mellon University" must not be used to
endorse or promote products derived from this software without
prior written permission. For permission or any legal
details, please contact
Office of Technology Transfer
Carnegie Mellon University
5000 Forbes Avenue
Pittsburgh, PA 15213-3890
(412) 268-4387, fax: (412) 268-7395
tech-transfer@andrew.cmu.edu
3b. The name(s) of the authors of this software must not be used to
endorse or promote products derived from this software without
prior written permission.
4. Redistributions of any form whatsoever must retain the following
acknowledgements:
"This product includes software developed by Computing Services
at Carnegie Mellon University (http://www.cmu.edu/computing/)."
"This product includes software developed by Paul Mackerras
<paulus@samba.org>".
"This product includes software developed by Pedro Roque Marques
<pedro_m@yahoo.com>".
"This product includes software developed by Tommi Komulainen
<Tommi.Komulainen@iki.fi>".
CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN
NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE FOR ANY SPECIAL, INDIRECT
OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
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TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
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