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NAME | SYNOPSIS | DESCRIPTION | FREQUENTLY USED OPTIONS | OPTIONS | PPPOE OPTIONS | OPTIONS FILES | SECURITY | AUTHENTICATION | ROUTING | MULTILINK | EXAMPLES | DIAGNOSTICS | EXIT STATUS | SCRIPTS | SEE ALSO | NOTES | AUTHORS | COPYRIGHT | COLOPHON |
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PPPD(8) System Manager's Manual PPPD(8)
pppd - Point-to-Point Protocol Daemon
pppd [ options ]
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.
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
Linux, 4.4BSD and NetBSD, any speed can be specified.
Other systems (e.g. 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.
defaultroute-metric
Define the metric of the defaultroute and only add it if
there is no other default route with the same metric.
With the default value of -1, the route is only added if
there is no default route at all.
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. This option is privileged.
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.
<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 and
the remote identifier is the remote IPv4 address (see
above). If the ipv6cp-use-remotenumber option is given,
the remote identifier is set to the value from
remotenumber option. 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
set local identifier. Otherwise both local and remote
identifiers are 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.
ca ca-file
(EAP-TLS, or PEAP) Use the file ca-file as the X.509
Certificate Authority (CA) file (in PEM format), needed
for setting up an EAP-TLS connection. This option is used
on the client-side in conjunction with the cert and key
options. Either ca, or capath options are required for
PEAP. EAP-TLS may also use the entry in eaptls-client or
eaptls-server for a CA certificate associated with a
particular peer.
capath path
(EAP-TLS, or PEAP) Specify a location that contains public
CA certificates. Either ca, or capath options are
required for PEAP.
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.
cert certfile
(EAP-TLS) Use the file certfile as the X.509 certificate
(in PEM format), needed for setting up an EAP-TLS
connection. This option is used on the client-side in
conjunction with the ca and key options.
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).
chap-timeout n
Set timeout for CHAP authentication by peer to n seconds
(default 60).
chapms-strip-domain
Some Windows 9x/ME clients might be transmitting the MS
domain before the username in the provided client name.
This option enables stripping the domain from the client
name on the server side before matching it against the
secret file.
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.
crl filename
(EAP-TLS, or PEAP) Use the file filename as the
Certificate Revocation List to check for the validity of
the peer's certificate. This option is not mandatory for
setting up a TLS connection. Also see the crl-dir option.
crl-dir directory
(EAP-TLS, or PEAP) Use the directory directory to scan for
CRL files in has format ($hash.r0) to check for the
validity of the peer's certificate. This option is not
mandatory for setting up a TLS connection. Also see the
crl option.
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.
defaultroute6
Add a default IPv6 route to the system routing tables,
using the peer as the gateway, when IPv6CP negotiation is
successfully completed. This entry is removed when the
PPP connection is broken. This option is privileged if
the nodefaultroute6 option has been specified. WARNING:
Do not enable this option by default. IPv6 routing tables
are managed by kernel (as apposite to IPv4) and IPv6
default route is configured by kernel automatically too
based on ICMPv6 Router Advertisement packets. This option
may conflict with kernel IPv6 route setup and should be
used only for broken IPv6 networks.
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-no-address
Disable negotiation of addresses via IP-Address IPCP
option.
ipcp-no-addresses
Disable negotiation of addresses via old-style deprecated
IP-Addresses IPCP option. pppd by default try to use new-
style IP-Address IPCP option. If new-style is not
supported by peer or is disabled by ipcp-no-address option
then pppd fallbacks to old-style deprecated IP-Addresses
IPCP option. When both new-style and old-style are
disabled by both ipcp-no-address and ipcp-no-addresses
options then negotiation of IP addresses is completely
disabled.
ipcp-restart n
Set the IPCP restart interval (retransmission timeout) to
n seconds (default 3).
ipparam string
Provides an extra parameter most of the notification
scripts, most notably ip-up, ip-pre-up, ip-down, ipv6-up,
ipv6-down, auth-up and auth-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-accept-remote
With this option, pppd will accept the peer's idea of its
(remote) IPv6 interface identifier, even if the remote
IPv6 interface identifier was specified in an option.
ipv6cp-noremote
Allow pppd to operate without having an IPv6 link local
address for the peer. This option is only available under
Linux. Normally, pppd will request the peer's IPv6
interface identifier (used for composing IPv6 link local
address), and if the peer does not supply it, pppd will
generate one for the peer. With this option, if the peer
does not supply its IPv6 interface identifier, pppd will
not ask the peer for it, and will not set the destination
IPv6 link local 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 IPv6 traffic until the peer starts
announcing ICMPv6 Router Advertisement or ICMPv6 Neighbor
Advertisement packets. Note that IPv6 router must
announce ICMPv6 Router Advertisement packets.
ipv6cp-nosendip
Don't send our local IPv6 interface identifier to peer
during IPv6 interface identifier negotiation.
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).
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.
key keyfile
(EAP-TLS) Use the file keyfile as the private key file (in
PEM format), needed for setting up an EAP-TLS connection.
This option is used on the client-side in conjunction with
the ca and cert options.
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-adaptive
If this option is used with the lcp-echo-failure option
then pppd will send LCP echo-request frames only if no
traffic was received from the peer since the last
echo-request was sent.
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).
lcp-rtt-file filename
Sets the file where the round-trip time (RTT) of LCP echo-
request frames will be logged.
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.
max-tls-sion string
(EAP-TLS, or PEAP) Configures the max allowed TLS version
used during negotiation with a peer. The default value
for this is 1.2. Values allowed for this option is 1.0.,
1.1, 1.2, 1.3.
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.)
netmask mask
Set the IPV4 network mask on the PPP interface to the
given mask, which can be given in dotted-quad notation or
as a single hexadecimal number preceded by 0x. This
option is not normally needed because the PPP interface is
a point-to-point connection, but in some specialized
circumstances it can be useful.
noaccomp
Disable Address/Control compression in both directions
(send and receive).
need-peer-eap
(EAP-TLS) Require the peer to verify our authentication
credentials.
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. This allows to
disable a replacedefaultroute option set previously in the
configuration.
nodefaultroute6
Disable the defaultroute6 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.
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).
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.
nosendip
Don't send our local IP address to peer during IP address
negotiation.
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.
stop-bits n
Set the number of stop bits for the serial port. Valid
values are 1 or 2. The default value is 1.
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.
tls-verify-method string
(EAP-TLS, or PEAP) Match the value specified for
remotename to that that of the X509 certificates subject
name, common name, or suffix of the common name.
Respective values allowed for this option is: none,
subject, name, or suffix. The default value for this
option is name.
tls-verify-key-usage
(EAP-TLS, or PEAP) Enables examination of peer
certificate's purpose, and extended key usage attributes.
unit num
Sets the ppp unit number (for a ppp0 or ppp1 etc interface
name) for outbound connections. If the unit is already in
use a dynamically allocated number will be used.
ifname string
Set the ppp interface name for outbound connections. If
the interface name is already in use, or if the name
cannot be used for any other reason, pppd will terminate.
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).
up_sdnotify
Use this option to run pppd in systemd service units of
Type=notify (up_sdnotify implies nodetach). When
up_sdnotify is enabled, pppd will notify systemd once it
has successfully established the ppp connection (to the
point where the first network control protocl, usually the
IP control protocol, has come up). This option is only
availble when pppd is compiled with systemd support.
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.
usepeerwins
Ask the peer for up to 2 WINS server addresses. The
addresses supplied by the peer (if any) are passed to the
/etc/ppp/ip-up script in the environment variables WINS1
and WINS2, and the environment variable USEPEERWINS will
be set to 1.
Please note that some modems (like the Huawei E220) requires this
option in order to avoid a race condition that results in the
incorrect DNS servers being assigned.
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.
To establish PPP link over Ethernet (PPPoE) it is needed to load
pppd's plugin pppoe.so and then specify option nic-interface
instead of modem options ttyname and speed. Recognized pppd's
PPPoE options are:
nic-interface
Use the ethernet device interface to communicate with the
peer. For example, establishing PPPoE link on eth0
interface is done by specifying ppp'd option nic-eth0.
Prefix nic- for this option may be avoided if interface
name is unambiguous and does not look like any other
pppd's option.
pppoe-service name
Connect to specified PPPoE service name. For backward
compatibility also rp_pppoe_service option name is
supported.
pppoe-ac name
Connect to specified PPPoE access concentrator name. For
backward compatibility also rp_pppoe_ac option name is
supported.
pppoe-sess sessid:macaddr
Attach to existing PPPoE session. For backward
compatibility also rp_pppoe_sess option name is supported.
pppoe-verbose n
Be verbose about discovered access concentrators. When set
to 2 or bigger value then dump also discovery packets. For
backward compatibility also rp_pppoe_verbose option name
is supported.
pppoe-mac macaddr
Connect to specified MAC address.
pppoe-host-uniq string
Set the PPPoE Host-Uniq tag to the supplied hex string.
By default PPPoE Host-Uniq tag is set to the pppd's
process PID. For backward compatibility this option may
be specified without pppoe- prefix.
pppoe-padi-timeout n
Initial timeout for discovery packets in seconds (default
5).
pppoe-padi-attempts n
Number of discovery attempts (default 3).
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.
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 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.
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 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.
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.
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.
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.
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 net-init, net-pre-up and ip-pre-up scripts). 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.
LLLOCAL
The Link-Local IPv6 address for the local end of the link.
This is only set when IPV6CP has come up.
LLREMOTE
The Link-Local IPv6 address for the remote end of the
link. This is only set when IPV6CP 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 (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).
WINS1 If the peer supplies WINS server addresses, this variable
is set to the first WINS server address supplied.
WINS2 If the peer supplies WINS server addresses, this variable
is set to the second WINS server address supplied.
ACNAME If the pppoe plugin is used to establish a connection to
an access concentrator (AC), this variable is set to the
name of the AC, as supplied by the AC.
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
ipparam
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.
WARNING: Please note that on systems where a single interface
carries multiple protocols (Linux) ip-pre-up is NOT actually
guaranteed to execute prior to the interface moving into an up
state, although IP information won't be known you should consider
using net-pre-up instead, alternatively, disable other NCPs such
that IPv4 is the only negotiated protocol - which will also
result in a guarantee that ip-pre-up is called prior to the
interface going into an UP state.
/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/net-init
This script will be executed the moment the ppp unit
number is known. This script will be waited for and
should not cause significant delays. This can be used to
update book-keeping type systems external to ppp and
provides the only guaranteed point where a script can be
executed knowing the ppp unit number prior to LCP being
initiated. It is executed with the parameters
interface-name tty-device speed ipparam
/etc/ppp/net-pre-up
This script will be executed just prior to NCP
negotiations initiating, and is guaranteed to be executed
whilst the interface (Linux) and/or sub-interfaces
(Solaris) as the case may be is/are still down. ppp will
block waiting for this script to complete, and the
interface may be safely renamed in this script (using for
example "ip li set dev $1 name ppp-foobar". The
parameters are the same as for net-init.
/etc/ppp/net-down
This script will be executed just prior to ppp terminating
and will not be waited for. The parameters are the same
as for net-init.
/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.
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.
RFC1990
Sklower, K.; et al., The PPP Multilink Protocol (MP).
August 1996.
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.
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.)
Paul Mackerras ([email protected]), based on earlier work by Drew
Perkins, Brad Clements, Karl Fox, Greg Christy, and Brad Parker.
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
[email protected]
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
<[email protected]>".
"This product includes software developed by Pedro Roque
Marques
<[email protected]>".
"This product includes software developed by Tommi Komulainen
<[email protected]>".
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 CONTRACT, NEGLIGENCE OR
OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE
USE OR PERFORMANCE OF THIS SOFTWARE.
THE AUTHORS OF THIS SOFTWARE DISCLAIM ALL WARRANTIES WITH REGARD
TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL THE AUTHORS 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 CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
PERFORMANCE OF THIS SOFTWARE.
This page is part of the ppp (An implementation of the Point-to-
Point Protocol (PPP)) project. Information about the project can
be found at ⟨https://ppp.samba.org/⟩. If you have a bug report
for this manual page, see
⟨https://github.com/paulusmack/ppp/issues⟩. This page was
obtained from the project's upstream Git repository
⟨https://github.com/paulusmack/ppp⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-05-18.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
PPPD(8)
Pages that refer to this page: pon(1), pppd-radattr(8), pppd-radius(8), pppdump(8), pppgetpass(8), pppstats(8), slattach(8), srp-entry(8)
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