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.
replacedefaultroute
This option is a flag to the defaultroute option. If
defaultroute is set and this flag is also set, pppd replaces an
existing default route with the new default route.
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 <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 must be
specified by the user on the command line or in an options file.
Pppd will initially configure the interface and enable it for IP
traffic without connecting to the peer. When traffic is
available, pppd will connect to the peer and perform
negotiation, authentication, etc. When this is completed, pppd
will commence passing data packets (i.e., IP packets) across the
link.
The 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-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 nuber 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.
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 adding a default route with pppd
can do so by placing this option in the /etc/ppp/options file.
noreplacedefaultroute
Disable the replacedefaultroute option. The system administrator
who wishes to prevent users from replacing a default route 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 not bring up the link for IP traffic. 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.
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.
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.
CALL_FILE
The value of the call option.
DNS1 If the peer supplies DNS server addresses, this variable is set
to the first DNS server address supplied.
DNS2 If the peer supplies DNS server addresses, this variable is set
to the second DNS server address supplied.
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/pppn.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
acknowledgments:
"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, DATA OR PROFITS, WHETHER IN AN ACTION OF
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