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.
mppc Enables MPPC (Microsoft Point to Point Compression).
This is the default.
mppe subopt1[,subopt2[,subopt3[..]]]
Modify MPPE (Microsoft Point to Point Encryption) parame‐
ters. In order for MPPE to successfully come up, you must
have authenticated with either MS-CHAP or MS-CHAPv2. By
default MPPE is optional, it means that pppd will not
propose MPPE to the peer, but will negotiate MPPE if peer
wants that. You can change this using required subop‐
tion. This option is presently only supported under
Linux, and only if your kernel has been configured to
include MPPE support.
MPPE suboptions:
required - require MPPE; disconnect if peer doesn't sup‐
port it,
stateless - try to negotiate stateless mode; default is
stateful,
no40 - disable 40 bit keys,
no56 - disable 56 bit keys,
no128 - disable 128 bit keys
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.
nomppc Disables MPPC (Microsoft Point to Point Compression).
nomppe Disables MPPE (Microsoft Point to Point Encryption).
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-mschap
Require the peer to authenticate itself using
MS-CHAP [Microsoft Challenge Handshake Authentica‐
tion Protocol] authentication.
require-mschap-v2
Require the peer to authenticate itself using
MS-CHAPv2 [Microsoft Challenge Handshake Authenti‐
cation Protocol, Version 2] authentication.
require-eap
Require the peer to authenticate itself using EAP
[Extensible Authentication Protocol] authentica‐
tion.
require-pap
Require the peer to authenticate itself using PAP
[Password Authentication Protocol] authentication.
show-password
When logging the contents of PAP packets, this
option causes pppd to show the password string in
the log message.
silent With this option, pppd will not transmit LCP pack‐
ets to initiate a connection until a valid LCP
packet is received from the peer (as for the `pas‐
sive' 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 light‐
weight 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_psuedonym
first as the identity, and save in this file any
pseudonym offered by the peer during authentica‐
tion.
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 Free‐
BSD 2.2.8 and later.
unit num
Sets the ppp unit number (for a ppp0 or ppp1 etc
interface name) for outbound connections.
updetach
With this option, pppd will detach from its con‐
trolling terminal once it has successfully estab‐
lished 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 sys‐
tem 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 envi‐
ronment variables DNS1 and DNS2, and the environ‐
ment variable USEPEERDNS will be set to 1. In
addition, pppd will create an /etc/ppp/resolv.conf
file containing one or two nameserver lines with
the address(es) supplied by the peer.
user name
Sets the name used for authenticating the local
system to the peer to name.
vj-max-slots n
Sets the number of connection slots to be used by
the Van Jacobson TCP/IP header compression and
decompression code to n, which must be between 2
and 16 (inclusive).
welcome script
Run the executable or shell command specified by
script before initiating PPP negotiation, after
the connect script (if any) has completed. A
value for this option from a privileged source
cannot be overridden by a non-privileged user.
xonxoff
Use software flow control (i.e. XON/XOFF) to con‐
trol 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 com‐
mand line. (In fact, the command-line options are
scanned to find the terminal name before the options.tty‐
name 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, delim‐
ited 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.
SECURITYpppd 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 unauthenti‐
cated 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. Privi‐
leged 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 creat‐
ing 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 per‐
mission to access. Otherwise pppd uses the invoking
user's real UID when opening the device.
AUTHENTICATION
Authentication is the process whereby one peer convinces
the other of its identity. This involves the first peer
sending its name to the other, together with some kind of
secret information which could only come from the genuine
authorized user of that name. In such an exchange, we
will call the first peer the "client" and the other the
"server". The client has a name by which it identifies
itself to the server, and the server also has a name by
which it identifies itself to the client. Generally the
genuine client shares some secret (or password) with the
server, and authenticates itself by proving that it knows
that secret. Very often, the names used for authentica‐
tion 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 initi‐
ates the CHAP authentication exchange by sending a chal‐
lenge 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 spec‐
ified 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 "!" indi‐
cates that the specified address is not acceptable. An
address may be followed by "/" and a number n, to indi‐
cate 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 indi‐
cate 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 authen‐
ticating 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 speci‐
fied 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 pass‐
word 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) compar‐
ison is omitted, for better security.
Furthermore, if the login option was specified, the user‐
name 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 authen‐
ticate 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. Communica‐
tion with other machines generally requires further modi‐
fication 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 exam‐
ple 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 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 end‐
point discriminator and the authenticated identity of the
peer (if it authenticates itself). The endpoint discrim‐
inator 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 num‐
bers. 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 dis‐
criminator 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 will‐
ing 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 sig‐
nal, it will terminate its link but not the bundle.
Note: demand mode is not currently supported with multi‐
link.
EXAMPLES
The following examples assume that the /etc/ppp/options
file contains the auth option (as in the default
/etc/ppp/options file in the ppp distribution).
Probably the most common use of pppd is to dial out to an
ISP. This can be done with a command such as
pppd call isp
where the /etc/ppp/peers/isp file is set up by the system
administrator to contain something like this:
ttyS0 19200 crtscts
connect '/usr/sbin/chat -v -f /etc/ppp/chat-isp'
noauth
In this example, we are using chat to dial the ISP's
modem and go through any logon sequence required. The
/etc/ppp/chat-isp file contains the script used by chat;
it could for example contain something like this:
ABORT "NO CARRIER"
ABORT "NO DIALTONE"
ABORT "ERROR"
ABORT "NO ANSWER"
ABORT "BUSY"
ABORT "Username/Password Incorrect"
"" "at"
OK "at&d0&c1"
OK "atdt2468135"
"name:" "^Umyuserid"
"word:" "\qmypassword"
"ispts" "\q^Uppp"
"~-^Uppp-~"
See the chat(8) man page for details of chat scripts.
Pppd can also be used to provide a dial-in ppp service
for users. If the users already have login accounts, the
simplest way to set up the ppp service is to let the
users log in to their accounts and run pppd (installed
setuid-root) with a command such as
pppd proxyarp
To allow a user to use the PPP facilities, you need to
allocate an IP address for that user's machine and create
an entry in /etc/ppp/pap-secrets, /etc/ppp/chap-secrets,
or /etc/ppp/srp-secrets (depending on which authentica‐
tion 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 "joe‐
spc" that is to be allowed to dial in to the machine
called "server" and use the IP address joespc.my.net, you
would add an entry like this to /etc/ppp/pap-secrets or
/etc/ppp/chap-secrets:
joespc server "joe's secret" joespc.my.net
(See srp-entry(8) for a means to generate the server's
entry when SRP-SHA1 is in use.) Alternatively, you can
create a username called (for example) "ppp", whose login
shell is pppd and whose home directory is /etc/ppp.
Options to be used when pppd is run this way can be put
in /etc/ppp/.ppprc.
If your serial connection is any more complicated than a
piece of wire, you may need to arrange for some control
characters to be escaped. In particular, it is often
useful to escape XON (^Q) and XOFF (^S), using asyncmap
a0000. If the path includes a telnet, you probably
should escape ^] as well (asyncmap 200a0000). If the
path includes an rlogin, you will need to use the escape
ff option on the end which is running the rlogin client,
since many rlogin implementations are not transparent;
they will remove the sequence [0xff, 0xff, 0x73, 0x73,
followed by any 8 bytes] from the stream.
DIAGNOSTICS
Messages are sent to the syslog daemon using facility
LOG_DAEMON. (This can be overridden by recompiling pppd
with the macro LOG_PPP defined as the desired facility.)
See the syslog(8) documentation for details of where the
syslog daemon will write the messages. On most systems,
the syslog daemon uses the /etc/syslog.conf file to spec‐
ify the destination(s) for syslog messages. You may need
to edit that file to suit.
The debug option causes the contents of all control pack‐
ets 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 ter‐
minated. 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 run‐
ning 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 proto‐
col (e.g. IP) was running.
11 The peer system failed (or refused) to authenti‐
cate itself.
12 The link was established successfully and termi‐
nated because it was idle.
13 The link was established successfully and termi‐
nated because the connect time limit was reached.
14 Callback was negotiated and an incoming call
should arrive shortly.
15 The link was terminated because the peer is not
responding to echo requests.
16 The link was terminated by the modem hanging up.
17 The PPP negotiation failed because serial loopback
was detected.
18 The init script failed (returned a non-zero exit
status).
19 We failed to authenticate ourselves to the peer.
SCRIPTS
Pppd invokes scripts at various stages in its processing
which can be used to perform site-specific ancillary pro‐
cessing. These scripts are usually shell scripts, but
could be executable code files instead. Pppd does not
wait for the scripts to finish (except for the ip-pre-up
script). The scripts are executed as root (with the real
and effective user-id set to 0), so that they can do
things such as update routing tables or run privileged
daemons. Be careful that the contents of these scripts
do not compromise your system's security. Pppd runs the
scripts with standard input, output and error redirected
to /dev/null, and with an environment that is empty
except for some environment variables that give informa‐
tion about the link. The environment variables that pppd
sets are:
DEVICE The name of the serial tty device being used.
IFNAME The name of the network interface being used.
IPLOCAL
The IP address for the local end of the link.
This is only set when IPCP has come up.
IPREMOTE
The IP address for the remote end of the link.
This is only set when IPCP has come up.
PEERNAME
The authenticated name of the peer. This is only
set if the peer authenticates itself.
SPEED The baud rate of the tty device.
ORIG_UID
The real user-id of the user who invoked pppd.
PPPLOGNAME
The username of the real user-id that invoked
pppd. This is always set.
For the ip-down and auth-down scripts, pppd also sets the
following variables giving statistics for the connection:
CONNECT_TIME
The number of seconds from when the PPP negotia‐
tion 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 exe‐
cuted 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 receiv‐
ing IPv6 packets. It is executed with the parame‐
ters
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 exe‐
cuted 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-pro‐
tocol local-IPX-router-name remote-IPX-router-name
ipparam pppd-pid
The local-IPX-routing-protocol and
remote-IPX-routing-protocol field may be one of
the following:
NONE to indicate that there is no routing
protocol
RIP to indicate that RIP/SAP should be used
NLSP to indicate that Novell NLSP should be
used
RIP NLSP to indicate that both RIP/SAP and NLSP
should be used
/etc/ppp/ipx-down
A program or script which is executed when the
link is no longer available for sending and
receiving IPX packets. This script can be used
for undoing the effects of the /etc/ppp/ipx-up
script. It is invoked in the same manner and with
the same parameters as the ipx-up script.
FILES
/var/run/pppn.pid (BSD or Linux), /etc/ppp/pppn.pid (oth‐
ers)
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 pro‐
cesses, interfaces and links, used for matching
links to bundles in multilink operation. May be
examined by external programs to obtain informa‐
tion about running pppd instances, the interfaces
and devices they are using, IP address assign‐
ments, 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 authenti‐
cation. 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 warn‐
ing if this is not the case.
~/.ppp_pseudonym
Saved client-side SRP-SHA1 pseudonym. See the
srp-use-pseudonym option for details.
/etc/ppp/options
System default options for pppd, read before user
default options or command-line options.
~/.ppprc
User default options, read before
/etc/ppp/options.ttyname.
/etc/ppp/options.ttyname
System default options for the serial port being
used, read after ~/.ppprc. In forming the ttyname
part of this filename, an initial /dev/ is
stripped from the port name (if present), and any
slashes in the remaining part are converted to
dots.
/etc/ppp/peers
A directory containing options files which may
contain privileged options, even if pppd was
invoked by a user other than root. The system
administrator can create options files in this
directory to permit non-privileged users to dial
out without requiring the peer to authenticate,
but only to certain trusted peers.
SEE 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 Proto‐
col (IPCP). May 1992.
RFC1334
Lloyd, B.; Simpson, W.A. PPP authentication pro‐
tocols. 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 Authen‐
tication Protocol (EAP). March 1998.
RFC2472
Haskin, D. IP Version 6 over PPP December 1998.
RFC2945
Wu, T., The SRP Authentication and Key Exchange
System September 2000.
draft-ietf-pppext-eap-srp-03.txt
Carlson, J.; et al., EAP SRP-SHA1 Authentication
Protocol. July 2001.
NOTES
Some limited degree of control can be exercised over a
running pppd process by sending it a signal from the list
below.
SIGINT, SIGTERM
These signals cause pppd to terminate the link (by
closing LCP), restore the serial device settings,
and exit. If a connector or disconnector process
is currently running, pppd will send the same sig‐
nal 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 compres‐
sion. 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 implemen‐
tation.)
AUTHORS
Paul Mackerras (paulus@samba.org), based on earlier work
by Drew Perkins, Brad Clements, Karl Fox, Greg Christy,
and Brad Parker.
COPYRIGHT
Pppd is copyrighted and made available under conditions
which provide that it may be copied and used in source or
binary forms provided that the conditions listed below
are met. Portions of pppd are covered by the following
copyright notices:
Copyright (c) 1984-2000 Carnegie Mellon University. All
rights reserved.
Copyright (c) 1993-2004 Paul Mackerras. All rights
reserved.
Copyright (c) 1995 Pedro Roque Marques. All rights
reserved.
Copyright (c) 1995 Eric Rosenquist. All rights reserved.
Copyright (c) 1999 Tommi Komulainen. All rights
reserved.
Copyright (C) Andrew Tridgell 1999
Copyright (c) 2000 by Sun Microsystems, Inc. All rights
reserved.
Copyright (c) 2001 by Sun Microsystems, Inc. All rights
reserved.
Copyright (c) 2002 Google, Inc. All rights reserved.
The copyright notices contain the following statements.
Redistribution and use in source and binary forms, with
or without modification, are permitted provided that the
following conditions are met:
1. Redistributions of source code must retain the above
copyright
notice, this list of conditions and the following dis‐
claimer.
2. Redistributions in binary form must reproduce the
above copyright
notice, this list of conditions and the following dis‐
claimer in
the documentation and/or other materials provided with
the
distribution.
3. The name "Carnegie Mellon University" must not be used
to
endorse or promote products derived from this software
without
prior written permission. For permission or any legal
details, please contact
Office of Technology Transfer
Carnegie Mellon University
5000 Forbes Avenue
Pittsburgh, PA 15213-3890
(412) 268-4387, fax: (412) 268-7395
tech-transfer@andrew.cmu.edu
3b. The name(s) of the authors of this software must not
be used to
endorse or promote products derived from this software
without
prior written permission.
4. Redistributions of any form whatsoever must retain the
following
acknowledgments:
"This product includes software developed by Computing
Services
at Carnegie Mellon University
(http://www.cmu.edu/computing/)."
"This product includes software developed by Paul
Mackerras
<paulus@samba.org>".
"This product includes software developed by Pedro
Roque Marques
<pedro_m@yahoo.com>".
"This product includes software developed by Tommi
Komulainen
<Tommi.Komulainen@iki.fi>".
CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH
REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES
OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL
CARNEGIE MELLON UNIVERSITY BE LIABLE FOR ANY SPECIAL,
INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSO‐
EVER 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 CONSEQUEN‐
TIAL 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.
PPPD(8)
