PPPD(8)PPPD(8)NAMEpppd - Point-to-Point Protocol Daemon
SYNOPSISpppd [ 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 infor‐
mation 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 con‐
nected to the standard input is given, pppd will use that termi‐
nal, 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 Net‐
BSD, 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-privi‐
leged 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 inter‐
face. 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 spec‐
ified. multipledefaultroutes This option is a flag to the
defaultroute option. If defaultroute is set and this flag is
also set, pppd will add the new default route even if there is
already a default route, allowing multiple default routes.
disconnect script
Execute the command specified by script, by passing it to
a shell, after pppd has terminated the link. This com‐
mand 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 net‐
work 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 spec‐
ified 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 speci‐
fied 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 inappro‐
priate 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 quali‐
fiers.
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 cor‐
responding direction. Use nobsdcomp or bsdcomp 0 to dis‐
able 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 nei‐
ther the crtscts, the nocrtscts, the cdtrcts nor the
nocdtrcts option is given, the hardware flow control set‐
ting 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 pro‐
cesses (such as the command specified with the pty com‐
mand) 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 sec‐
ond). 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 pack‐
ets 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 sys‐
log.conf(5)).
noext-traffic
Do not count incoming traffic against the idle time set
with the idle option. The default idle option behavior
is to count both outgoing and incoming traffic. This can
be very helpful when remote hosts keeping sending
unwanted traffic, thereby keeping the connection up.
Note that this cannot prevent programs from responding to
incoming requests and in doing so defeat the idle option.
The route program reject parameter might help in that
case when enough is known about IP address space of the
site generating the unwanted requests. If you initiated
contact with the site generating the requests, say with a
web browser, then denying ingress with the "reject"
parameter probably won't be a viable option.
default-asyncmap Disable asyncmap negotiation, forcing
all control characters to be escaped for both the trans‐
mit 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. Alterna‐
tively, 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-Com‐
press 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 inter‐
face 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 conjuction 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 privi‐
leged.
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 ether‐
net 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 discrimi‐
nator 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 speci‐
fied 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 trans‐
missions 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 trans‐
missions 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 trans‐
missions 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 trans‐
missions 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 speci‐
fied, the network number is obtained from the peer. If
the peer does not have the network number, the IPX proto‐
col will not be started.
ipx-node n:m
Set the IPX node numbers. The two node numbers are sepa‐
rated 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 speci‐
fied, 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 termi‐
nate 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 transmis‐
sions 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 transmis‐
sions 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 responsi‐
ble for the link to a given peer system. This is a priv‐
ileged 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 oppo‐
site 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-ses‐
sion 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 exe‐
cuting 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 mul‐
tilink bundle, and is analogous to the MRU for the indi‐
vidual 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 pur‐
poses 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 negotia‐
tion.
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 administra‐
tor who wishes to prevent users from creating default
routes with pppd can do so by placing this option in the
/etc/ppp/options file.
nodeflate
Disables Deflate compression; pppd will not request or
agree to compress packets using the Deflate scheme.
nodetach
Don't detach from the controlling terminal. Without this
option, if a serial device other than the terminal on the
standard input is specified, pppd will fork to become a
background process.
noendpoint
Disables pppd from sending an endpoint discriminator to
the peer or accepting one from the peer (see the MULTI‐
LINK 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 negotia‐
tion.
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 cur‐
rently 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 avail‐
able under Linux, and only has any effect if multilink is
enabled.
nomultilink
Disables the use of PPP multilink. This option is cur‐
rently 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 mas‐
ter/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 mas‐
ter 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 trans‐
missions 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 fire‐
wall 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 avail‐
able under Linux, and requires that the kernel was con‐
figured to include PPP filtering support (CONFIG_PPP_FIL‐
TER).
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 con‐
tain 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 transmit‐
ted frames with Predictor-1 if requested. This option
has no effect unless the kernel driver supports Predic‐
tor-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 mem‐
bers of group-name cannot use pppd to become root them‐
selves. 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 commu‐
nicate 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 conjuction 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 inter‐
face. 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 authentica‐
tion 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 [Chal‐
lenge Handshake Authentication Protocol] authentication.
require-mppe
Require the use of MPPE (Microsoft Point to Point Encryp‐
tion). 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 sup‐
port.
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 [Exten‐
sible Authentication Protocol] authentication.
require-pap
Require the peer to authenticate itself using PAP [Pass‐
word Authentication Protocol] authentication.
show-password
When logging the contents of PAP packets, this option
causes pppd to show the password string in the log mes‐
sage.
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 mecha‐
nism 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 gen‐
erate 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_psuedonym 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 asynchro‐
nous. 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 inter‐
face 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 name‐
server 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 fol‐
lowing 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.
SECURITYpppd provides system administrators with sufficient access con‐
trol 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 authenti‐
cate themselves in order to set up a connection. On such a sys‐
tem, the auth option is the default. On the other hand, a sys‐
tem 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 privi‐
leged, which means that they may not be used by an ordinary non-
privileged user running a setuid-root pppd, either on the com‐
mand 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 administra‐
tor. 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 connec‐
tion 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. Gener‐
ally 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 cor‐
respond 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 dic‐
tionary-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 par‐
ticular 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 net‐
work 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 authenti‐
cating 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 net‐
work 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 recom‐
mended.
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 discrimina‐
tor and the authenticated identity of the peer (if it authenti‐
cates 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 discrimina‐
tor 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 termi‐
nates, 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 admin‐
istrator 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 con‐
tain 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 com‐
mand 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 joe‐
spc.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 user‐
name 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_DAE‐
MON. (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 val‐
ues used are:
0 Pppd has detached, or otherwise the connection was suc‐
cessfully 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 vir‐
tual 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 sta‐
tus).
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 respond‐
ing 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 fin‐
ish (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 privi‐
leged 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 environ‐
ment variables that give information about the link. The envi‐
ronment 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 fol‐
lowing variables giving statistics for the connection:
CONNECT_TIME
The number of seconds from when the PPP negotiation
started until the connection was terminated.
BYTES_SENT
The number of bytes sent (at the level of the serial
port) during the connection.
BYTES_RCVD
The number of bytes received (at the level of the serial
port) during the connection.
LINKNAME
The logical name of the link, set with the linkname
option.
DNS1 If the peer supplies DNS server addresses, this variable
is set to the first DNS server address supplied.
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 inter‐
face. 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-rout‐
ing-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 pro‐
grams to obtain information about running pppd instances,
the interfaces and devices they are using, IP address
assignments, etc. /etc/ppp/pap-secrets Usernames, pass‐
words 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.tty‐
name.
/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 authenti‐
cate, but only to certain trusted peers.
SEE ALSOchat(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 Proto‐
col. 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 clos‐
ing LCP), restore the serial device settings, and exit.
If a connector or disconnector process is currently run‐
ning, 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 immedi‐
ately. If a connector or disconnector process is run‐
ning, 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 with‐
out modification, are permitted provided that the following con‐
ditions are met:
1. Redistributions of source code must retain the above copy‐
right
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copy‐
right
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 with‐
out
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 with‐
out
prior written permission.
4. Redistributions of any form whatsoever must retain the fol‐
lowing
acknowledgments:
"This product includes software developed by Computing Ser‐
vices
at Carnegie Mellon University (http://www.cmu.edu/comput‐
ing/)."
"This product includes software developed by Paul Mackerras
<paulus@samba.org>".
"This product includes software developed by Pedro Roque Mar‐
ques
<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 MER‐
CHANTABILITY AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNI‐
VERSITY 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 MER‐
CHANTABILITY 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 PERFOR‐
MANCE OF THIS SOFTWARE.
PPPD(8)
