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PPPD(8) PPPD(8)
NAME
pppd - Point-to-Point Protocol Daemon
SYNOPSIS
pppd [ options ]
DESCRIPTION
PPP is the protocol used for establishing internet links over dial-up modems, DSL
connections, and many other types of point-to-point links. The pppd daemon works
together with the kernel PPP driver to establish and maintain a PPP link with
another system (called the peer) and to negotiate Internet Protocol (IP) addresses
for each end of the link. Pppd can also authenticate the peer and/or supply
authentication information to the peer. PPP can be used with other network proto-
cols besides IP, but such use is becoming increasingly rare.
FREQUENTLY USED OPTIONS
ttyname
Use the serial port called ttyname to communicate with the peer. The string
"/dev/" is prepended to ttyname to form the name of the device to open. If
no device name is given, or if the name of the terminal connected to the
standard input is given, pppd will use that terminal, and will not fork to
put itself in the background. A value for this option from a privileged
source cannot be overridden by a non-privileged user.
speed An option that is a decimal number is taken as the desired baud rate for the
serial device. On systems such as 4.4BSD and NetBSD, any speed can be spec-
ified. 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 char-
acters with values from 0 to 31, where a 1 bit indicates that the corre-
sponding 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 options from the file /etc/ppp/peers/name. This file may contain priv-
ileged 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, com-
mands 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 privi-
leged source cannot be overridden by a non-privileged user.
crtscts
Specifies that pppd should set the serial port to use hardware flow control
using the RTS and CTS signals in the RS-232 interface. If neither the
crtscts, the nocrtscts, the cdtrcts nor the nocdtrcts option is given, the
hardware flow control setting for the serial port is left unchanged. Some
serial ports (such as Macintosh serial ports) lack a true RTS output. Such
serial ports use this mode to implement unidirectional flow control. The
serial port will suspend transmission when requested by the modem (via CTS)
but will be unable to request the modem to stop sending to the computer.
This mode retains the ability to use DTR as a modem control line.
defaultroute
Add a default route to the system routing tables, using the peer as the
gateway, when IPCP negotiation is successfully completed. This entry is
removed when the PPP connection is broken. This option is privileged if the
nodefaultroute option has been specified.
disconnect script
Execute the command specified by script, by passing it to a shell, after
pppd has terminated the link. This command could, for example, issue com-
mands 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 (regard-
less 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 speci-
fied 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 ini-
tialize the serial line. This script would typically use the chat(8) pro-
gram 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.
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 net-
working 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 omit-
ted. The IP addresses can be specified with a host name or in decimal dot
notation (e.g. 150.234.56.78). The default local address is the (first) IP
address of the system (unless the noipdefault option is given). The remote
address will be obtained from the peer if not specified in any option.
Thus, in simple cases, this option is not required. If a local and/or
remote IP address is specified with this option, pppd will not accept a dif-
ferent value from the peer in the IPCP negotiation, unless the ipcp-accept-
local and/or ipcp-accept-remote options are given, respectively.
ipv6 <local_interface_identifier>,<remote_interface_identifier>
Set the local and/or remote 64-bit interface identifier. Either one may be
omitted. The identifier must be specified in standard ascii notation of IPv6
addresses (e.g. ::dead:beef). If the ipv6cp-use-ipaddr option is given, the
local identifier is the local IPv4 address (see above). On systems which
supports a unique persistent id, such as EUI-48 derived from the Ethernet
MAC address, ipv6cp-use-persistent option can be used to replace the ipv6
<local>,<remote> option. Otherwise the identifier is randomized.
active-filter filter-expression
Specifies a packet filter to be applied to data packets to determine which
packets are to be regarded as link activity, and therefore reset the idle
timer, or cause the link to be brought up in demand-dialling mode. This
option is useful in conjunction with the idle option if there are packets
being sent or received regularly over the link (for example, routing infor-
mation packets) which would otherwise prevent the link from ever appearing
to be idle. The filter-expression syntax is as described for tcpdump(1),
except that qualifiers which are inappropriate for a PPP link, such as ether
and arp, are not permitted. Generally the filter expression should be
enclosed in single-quotes to prevent whitespace in the expression from being
interpreted by the shell. This option is currently only available under
Linux, and requires that the kernel was configured to include PPP filtering
support (CONFIG_PPP_FILTER). Note that it is possible to apply different
constraints to incoming and outgoing packets using the inbound and outbound
qualifiers.
allow-ip address(es)
Allow peers to use the given IP address or subnet without authenticating
themselves. The parameter is parsed as for each element of the list of
allowed IP addresses in the secrets files (see the AUTHENTICATION section
below).
allow-number number
Allow peers to connect from the given telephone number. A trailing ‘*’
character will match all numbers beginning with the leading part.
bsdcomp nr,nt
Request that the peer compress packets that it sends, using the BSD-Compress
scheme, with a maximum code size of nr bits, and agree to compress packets
sent to the peer with a maximum code size of nt bits. If nt is not speci-
fied, it defaults to the value given for nr. Values in the range 9 to 15
may be used for nr and nt; larger values give better compression but consume
more kernel memory for compression dictionaries. Alternatively, a value of
0 for nr or nt disables compression in the corresponding direction. Use
nobsdcomp or bsdcomp 0 to disable BSD-Compress compression entirely.
cdtrcts
Use a non-standard hardware flow control (i.e. DTR/CTS) to control the flow
of data on the serial port. If neither the crtscts, the nocrtscts, the
cdtrcts nor the nocdtrcts option is given, the hardware flow control setting
for the serial port is left unchanged. Some serial ports (such as Macintosh
serial ports) lack a true RTS output. Such serial ports use this mode to
implement true bi-directional flow control. The sacrifice is that this flow
control mode does not permit using DTR as a modem control line.
chap-interval n
If this option is given, pppd will rechallenge the peer every n seconds.
chap-max-challenge n
Set the maximum number of CHAP challenge transmissions to n (default 10).
chap-restart n
Set the CHAP restart interval (retransmission timeout for challenges) to n
seconds (default 3).
connect-delay n
Wait for up n milliseconds after the connect script finishes for a valid PPP
packet from the peer. At the end of this time, or when a valid PPP packet
is received from the peer, pppd will commence negotiation by sending its
first LCP packet. The default value is 1000 (1 second). This wait period
only applies if the connect or pty option is used.
debug Enables connection debugging facilities. If this option is given, pppd will
log the contents of all control packets sent or received in a readable form.
The packets are logged through syslog with facility daemon and level debug.
This information can be directed to a file by setting up /etc/syslog.conf
appropriately (see syslog.conf(5)).
default-asyncmap
Disable asyncmap negotiation, forcing all control characters to be escaped
for both the transmit and the receive direction.
default-mru
Disable MRU [Maximum Receive Unit] negotiation. With this option, pppd will
use the default MRU value of 1500 bytes for both the transmit and receive
direction.
deflate nr,nt
Request that the peer compress packets that it sends, using the Deflate
scheme, with a maximum window size of 2**nr bytes, and agree to compress
packets sent to the peer with a maximum window size of 2**nt bytes. If nt
is not specified, it defaults to the value given for nr. Values in the
range 9 to 15 may be used for nr and nt; larger values give better compres-
sion 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-
Compress if the peer can do either.)
demand Initiate the link only on demand, i.e. when data traffic is present. With
this option, the remote IP address must be specified by the user on the com-
mand 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 quali-
fied domain name is porsche.Quotron.COM, you could specify domain
Quotron.COM. Pppd would then use the name porsche.Quotron.COM for looking
up secrets in the secrets file, and as the default name to send to the peer
when authenticating itself to the peer. This option is privileged.
dryrun With the dryrun option, pppd will print out all the option values which have
been set and then exit, after parsing the command line and options files and
checking the option values, but before initiating the link. The option val-
ues 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 communi-
cate 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.
endpoint <epdisc>
Sets the endpoint discriminator sent by the local machine to the peer during
multilink negotiation to <epdisc>. The default is to use the MAC address of
the first ethernet interface on the system, if any, otherwise the IPv4
address corresponding to the hostname, if any, provided it is not in the
multicast or locally-assigned IP address ranges, or the localhost address.
The endpoint discriminator can be the string null or of the form type:value,
where type is a decimal number or one of the strings local, IP, MAC, magic,
or phone. The value is an IP address in dotted-decimal notation for the IP
type, or a string of bytes in hexadecimal, separated by periods or colons
for the other types. For the MAC type, the value may also be the name of an
ethernet or similar network interface. This option is currently only avail-
able 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 (authen-
ticator). (Default is 3 seconds.)
eap-timeout n
Set the maximum time to wait for the peer to send an EAP Request when acting
as a client (authenticatee). (Default is 20 seconds.)
hide-password
When logging the contents of PAP packets, this option causes pppd to exclude
the password string from the log. This is the default.
holdoff n
Specifies how many seconds to wait before re-initiating the link after it
terminates. This option only has any effect if the persist or demand option
is used. The holdoff period is not applied if the link was terminated
because it was idle.
idle n Specifies that pppd should disconnect if the link is idle for n seconds.
The link is idle when no data packets (i.e. IP packets) are being sent or
received. Note: it is not advisable to use this option with the persist
option without the demand option. If the active-filter option is given,
data packets which are rejected by the specified activity filter also count
as the link being idle.
ipcp-accept-local
With this option, pppd will accept the peer’s idea of our local IP address,
even if the local IP address was specified in an option.
ipcp-accept-remote
With this option, pppd will accept the peer’s idea of its (remote) IP
address, even if the remote IP address was specified in an option.
ipcp-max-configure n
Set the maximum number of IPCP configure-request transmissions to n (default
10).
ipcp-max-failure n
Set the maximum number of IPCP configure-NAKs returned before starting to
send configure-Rejects instead to n (default 10).
ipcp-max-terminate n
Set the maximum number of IPCP terminate-request transmissions to n (default
3).
ipcp-restart n
Set the IPCP restart interval (retransmission timeout) to n seconds (default
3).
ipparam string
Provides an extra parameter to the ip-up and ip-down scripts. If this
option is given, the string supplied is given as the 6th parameter to those
scripts.
ipv6cp-max-configure n
Set the maximum number of IPv6CP configure-request transmissions to n
(default 10).
ipv6cp-max-failure n
Set the maximum number of IPv6CP configure-NAKs returned before starting to
send configure-Rejects instead to n (default 10).
ipv6cp-max-terminate n
Set the maximum number of IPv6CP terminate-request transmissions to n
(default 3).
ipv6cp-restart n
Set the IPv6CP restart interval (retransmission timeout) to n seconds
(default 3).
ipx Enable the IPXCP and IPX protocols. This option is presently only supported
under Linux, and only if your kernel has been configured to include IPX sup-
port.
ipx-network n
Set the IPX network number in the IPXCP configure request frame to n, a hex-
adecimal number (without a leading 0x). There is no valid default. If this
option is not specified, the network number is obtained from the peer. If
the peer does not have the network number, the IPX protocol will not be
started.
ipx-node n:m
Set the IPX node numbers. The two node numbers are separated from each other
with a colon character. The first number n is the local node number. The
second number m is the peer’s node number. Each node number is a hexadecimal
number, at most 10 digits long. The node numbers on the ipx-network must be
unique. There is no valid default. If this option is not specified then the
node numbers are obtained from the peer.
ipx-router-name <string>
Set the name of the router. This is a string and is sent to the peer as
information data.
ipx-routing n
Set the routing protocol to be received by this option. More than one
instance of ipx-routing may be specified. The ’none’ option (0) may be
specified as the only instance of ipx-routing. The values may be 0 for NONE,
2 for RIP/SAP, and 4 for NLSP.
ipxcp-accept-local
Accept the peer’s NAK for the node number specified in the ipx-node option.
If a node number was specified, and non-zero, the default is to insist that
the value be used. If you include this option then you will permit the peer
to override the entry of the node number.
ipxcp-accept-network
Accept the peer’s NAK for the network number specified in the ipx-network
option. If a network number was specified, and non-zero, the default is to
insist that the value be used. If you include this option then you will per-
mit 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 mes-
sages, 2 to request that the contents of received packets be printed, and 4
to request that the contents of transmitted packets be printed. On most
systems, messages printed by the kernel are logged by syslog(1) to a file as
directed in the /etc/syslog.conf configuration file.
ktune Enables pppd to alter kernel settings as appropriate. Under Linux, pppd
will enable IP forwarding (i.e. set /proc/sys/net/ipv4/ip_forward to 1) if
the proxyarp option is used, and will enable the dynamic IP address option
(i.e. set /proc/sys/net/ipv4/ip_dynaddr to 1) in demand mode if the local
address changes.
lcp-echo-failure n
If this option is given, pppd will presume the peer to be dead if n LCP
echo-requests are sent without receiving a valid LCP echo-reply. If this
happens, pppd will terminate the connection. Use of this option requires a
non-zero value for the lcp-echo-interval parameter. This option can be used
to enable pppd to terminate after the physical connection has been broken
(e.g., the modem has hung up) in situations where no hardware modem control
lines are available.
lcp-echo-interval n
If this option is given, pppd will send an LCP echo-request frame to the
peer every n seconds. Normally the peer should respond to the echo-request
by sending an echo-reply. This option can be used with the lcp-echo-failure
option to detect that the peer is no longer connected.
lcp-max-configure n
Set the maximum number of LCP configure-request transmissions to n (default
10).
lcp-max-failure n
Set the maximum number of LCP configure-NAKs returned before starting to
send configure-Rejects instead to n (default 10).
lcp-max-terminate n
Set the maximum number of LCP terminate-request transmissions to n (default
3).
lcp-restart n
Set the LCP restart interval (retransmission timeout) to n seconds (default
3).
linkname name
Sets the logical name of the link to name. Pppd will create a file named
ppp-name.pid in /var/run (or /etc/ppp on some systems) containing its pro-
cess ID. This can be useful in determining which instance of pppd is
responsible for the link to a given peer system. This is a privileged
option.
local Don’t use the modem control lines. With this option, pppd will ignore the
state of the CD (Carrier Detect) signal from the modem and will not change
the state of the DTR (Data Terminal Ready) signal.
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 mes-
sages 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.
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 speci-
fied), and it will drop the DTR (Data Terminal Ready) signal briefly when
the connection is terminated and before executing the connect script. On
Ultrix, this option implies hardware flow control, as for the crtscts
option.
mp Enables the use of PPP multilink; this is an alias for the ‘multilink’
option. This option is currently only available under Linux.
mppe-stateful
Allow MPPE to use stateful mode. Stateless mode is still attempted first.
The default is to disallow stateful mode.
mpshortseq
Enables the use of short (12-bit) sequence numbers in multilink headers, as
opposed to 24-bit sequence numbers. This option is only available under
Linux, and only has any effect if multilink is enabled (see the multilink
option).
mrru n Sets the Maximum Reconstructed Receive Unit to n. The MRRU is the maximum
size for a received packet on a multilink bundle, and is analogous to the
MRU for the individual links. This option is currently only available under
Linux, and only has any effect if multilink is enabled (see the multilink
option).
ms-dns <addr>
If pppd is acting as a server for Microsoft Windows clients, this option
allows pppd to supply one or two DNS (Domain Name Server) addresses to the
clients. The first instance of this option specifies the primary DNS
address; the second instance (if given) specifies the secondary DNS address.
(This option was present in some older versions of pppd under the name dns-
addr.)
ms-wins <addr>
If pppd is acting as a server for Microsoft Windows or "Samba" clients, this
option allows pppd to supply one or two WINS (Windows Internet Name Ser-
vices) 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 sys-
tem and the peer. If there is an existing bundle to the peer, pppd will
join this link to that bundle, otherwise pppd will create a new bundle. See
the MULTILINK section below. This option is currently only available under
Linux.
name name
Set the name of the local system for authentication purposes to name. This
is a privileged option. With this option, pppd will use lines in the
secrets files which have name as the second field when looking for a secret
to use in authenticating the peer. In addition, unless overridden with the
user option, name will be used as the name to send to the peer when authen-
ticating 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 com-
press packets using the BSD-Compress scheme.
noccp Disable CCP (Compression Control Protocol) negotiation. This option should
only be required if the peer is buggy and gets confused by requests from
pppd for CCP negotiation.
nocrtscts
Disable hardware flow control (i.e. RTS/CTS) on the serial port. If neither
the crtscts nor the nocrtscts nor the cdtrcts nor the nocdtrcts option is
given, the hardware flow control setting for the serial port is left
unchanged.
nocdtrcts
This option is a synonym for nocrtscts. Either of these options will disable
both forms of hardware flow control.
nodefaultroute
Disable the defaultroute option. The system administrator who wishes to
prevent users from creating default routes with pppd can do so by placing
this option in the /etc/ppp/options file.
nodeflate
Disables Deflate compression; pppd will not request or agree to compress
packets using the Deflate scheme.
nodetach
Don’t detach from the controlling terminal. Without this option, if a
serial device other than the terminal on the standard input is specified,
pppd will fork to become a background process.
noendpoint
Disables pppd from sending an endpoint discriminator to the peer or accept-
ing one from the peer (see the MULTILINK section below). This option should
only be required if the peer is buggy.
noip Disable IPCP negotiation and IP communication. This option should only be
required if the peer is buggy and gets confused by requests from pppd for
IPCP negotiation.
noipv6 Disable IPv6CP negotiation and IPv6 communication. This option should only
be required if the peer is buggy and gets confused by requests from pppd for
IPv6CP negotiation.
noipdefault
Disables the default behaviour when no local IP address is specified, which
is to determine (if possible) the local IP address from the hostname. With
this option, the peer will have to supply the local IP address during IPCP
negotiation (unless it specified explicitly on the command line or in an
options file).
noipx Disable the IPXCP and IPX protocols. This option should only be required if
the peer is buggy and gets confused by requests from pppd for IPXCP negotia-
tion.
noktune
Opposite of the ktune option; disables pppd from changing system settings.
nolog Do not send log messages to a file or file descriptor. This option cancels
the logfd and logfile options.
nomagic
Disable magic number negotiation. With this option, pppd cannot detect a
looped-back line. This option should only be needed if the peer is buggy.
nomp Disables the use of PPP multilink. This option is currently only available
under Linux.
nomppe Disables MPPE (Microsoft Point to Point Encryption). This is the default.
nomppe-40
Disable 40-bit encryption with MPPE.
nomppe-128
Disable 128-bit encryption with MPPE.
nomppe-stateful
Disable MPPE stateful mode. This is the default.
nompshortseq
Disables the use of short (12-bit) sequence numbers in the PPP multilink
protocol, forcing the use of 24-bit sequence numbers. This option is cur-
rently only available under Linux, and only has any effect if multilink is
enabled.
nomultilink
Disables the use of PPP multilink. This option is currently only available
under Linux.
nopcomp
Disable protocol field compression negotiation in both the receive and the
transmit direction.
nopersist
Exit once a connection has been made and terminated. This is the default
unless the persist or demand option has been specified.
nopredictor1
Do not accept or agree to Predictor-1 compression.
noproxyarp
Disable the proxyarp option. The system administrator who wishes to prevent
users from creating proxy ARP entries with pppd can do so by placing this
option in the /etc/ppp/options file.
notty Normally, pppd requires a terminal device. With this option, pppd will
allocate itself a pseudo-tty master/slave pair and use the slave as its ter-
minal device. Pppd will create a child process to act as a ‘character
shunt’ to transfer characters between the pseudo-tty master and its standard
input and output. Thus pppd will transmit characters on its standard output
and receive characters on its standard input even if they are not terminal
devices. This option increases the latency and CPU overhead of transferring
data over the ppp interface as all of the characters sent and received must
flow through the character shunt process. An explicit device name may not
be given if this option is used.
novj Disable Van Jacobson style TCP/IP header compression in both the transmit
and the receive direction.
novjccomp
Disable the connection-ID compression option in Van Jacobson style TCP/IP
header compression. With this option, pppd will not omit the connection-ID
byte from Van Jacobson compressed TCP/IP headers, nor ask the peer to do so.
papcrypt
Indicates that all secrets in the /etc/ppp/pap-secrets file which are used
for checking the identity of the peer are encrypted, and thus pppd should
not accept a password which, before encryption, is identical to the secret
from the /etc/ppp/pap-secrets file.
pap-max-authreq n
Set the maximum number of PAP authenticate-request transmissions to n
(default 10).
pap-restart n
Set the PAP restart interval (retransmission timeout) to n seconds (default
3).
pap-timeout n
Set the maximum time that pppd will wait for the peer to authenticate itself
with PAP to n seconds (0 means no limit).
pass-filter filter-expression
Specifies a packet filter to applied to data packets being sent or received
to determine which packets should be allowed to pass. Packets which are
rejected by the filter are silently discarded. This option can be used to
prevent specific network daemons (such as routed) using up link bandwidth,
or to provide a very basic firewall capability. The filter-expression syn-
tax is as described for tcpdump(1), except that qualifiers which are inap-
propriate for a PPP link, such as ether and arp, are not permitted. Gener-
ally 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 pack-
ets using the inbound and outbound qualifiers. This option is currently only
available under Linux, and requires that the kernel was configured to
include PPP filtering support (CONFIG_PPP_FILTER).
password password-string
Specifies the password to use for authenticating to the peer. Use of this
option is discouraged, as the password is likely to be visible to other
users on the system (for example, by using ps(1)).
persist
Do not exit after a connection is terminated; instead try to reopen the con-
nection. 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 privi-
leged option. If filename does not contain a slash (/), pppd will look in
the /usr/lib/pppd/version directory for the plugin, where version is the
version number of pppd (for example, 2.4.2).
predictor1
Request that the peer compress frames that it sends using Predictor-1 com-
pression, and agree to compress transmitted frames with Predictor-1 if
requested. This option has no effect unless the kernel driver supports Pre-
dictor-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 guaran-
tee that members of group-name cannot use pppd to become root themselves.
Consider it equivalent to putting the members of group-name in the kmem or
disk group.
proxyarp
Add an entry to this system’s ARP [Address Resolution Protocol] table with
the IP address of the peer and the Ethernet address of this system. This
will have the effect of making the peer appear to other systems to be on the
local ethernet.
pty script
Specifies that the command script is to be used to communicate rather than a
specific terminal device. Pppd will allocate itself a pseudo-tty mas-
ter/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 interface. The characters are stored in a tagged format
with timestamps, which can be displayed in readable form using the ppp-
dump(8) program.
remotename name
Set the assumed name of the remote system for authentication purposes to
name.
remotenumber number
Set the assumed telephone number of the remote system for authentication
purposes to number.
refuse-chap
With this option, pppd will not agree to authenticate itself to the peer
using CHAP.
refuse-mschap
With this option, pppd will not agree to authenticate itself to the peer
using MS-CHAP.
refuse-mschap-v2
With this option, pppd will not agree to authenticate itself to the peer
using MS-CHAPv2.
refuse-eap
With this option, pppd will not agree to authenticate itself to the peer
using EAP.
refuse-pap
With this option, pppd will not agree to authenticate itself to the peer
using PAP.
require-chap
Require the peer to authenticate itself using CHAP [Challenge Handshake
Authentication Protocol] authentication.
require-mppe
Require the use of MPPE (Microsoft Point to Point Encryption). This option
disables all other compression types. This option enables both 40-bit and
128-bit encryption. In order for MPPE to successfully come up, you must
have authenticated with either MS-CHAP or MS-CHAPv2. This option is
presently only supported under Linux, and only if your kernel has been con-
figured to include MPPE support.
require-mppe-40
Require the use of MPPE, with 40-bit encryption.
require-mppe-128
Require the use of MPPE, with 128-bit encryption.
require-mschap
Require the peer to authenticate itself using MS-CHAP [Microsft Challenge
Handshake Authentication Protocol] authentication.
require-mschap-v2
Require the peer to authenticate itself using MS-CHAPv2 [Microsft Challenge
Handshake Authentication Protocol, Version 2] authentication.
require-eap
Require the peer to authenticate itself using EAP [Extensible Authentication
Protocol] authentication.
require-pap
Require the peer to authenticate itself using PAP [Password Authentication
Protocol] authentication.
show-password
When logging the contents of PAP packets, this option causes pppd to show
the password string in the log message.
silent With this option, pppd will not transmit LCP packets to initiate a connec-
tion 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 lightweight SRP
rechallenge mechanism at intervals of n seconds. This option is faster than
eap-interval reauthentication because it uses a hash-based mechanism and
does not derive a new session key.
srp-pn-secret string
Set the long-term pseudonym-generating secret for the server. This value is
optional and if set, needs to be known at the server (authenticator) side
only, and should be different for each server (or poll of identical
servers). It is used along with the current date to generate a key to
encrypt and decrypt the client’s identity contained in the pseudonym.
srp-use-pseudonym
When operating as an EAP SRP-SHA1 client, attempt to use the pseudonym
stored in ~/.ppp_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 asynchronous. The device
used by pppd with this option must have sync support. Currently supports
Microgate SyncLink adapters under Linux and FreeBSD 2.2.8 and later.
unit num
Sets the ppp unit number (for a ppp0 or ppp1 etc interface name) for out-
bound 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 privi-
leged.
usepeerdns
Ask the peer for up to 2 DNS server addresses. The addresses supplied by
the peer (if any) are passed to the /etc/ppp/ip-up script in the environment
variables DNS1 and DNS2, and the environment variable USEPEERDNS will be set
to 1. In addition, pppd will create an /etc/ppp/resolv.conf file containing
one or two nameserver lines with the address(es) supplied by the peer.
user name
Sets the name used for authenticating the local system to the peer to name.
vj-max-slots n
Sets the number of connection slots to be used by the Van Jacobson TCP/IP
header compression and decompression code to n, which must be between 2 and
16 (inclusive).
welcome script
Run the executable or shell command specified by script before initiating
PPP negotiation, after the connect script (if any) has completed. A value
for this option from a privileged source cannot be overridden by a non-priv-
ileged 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. Whites-
pace can be included in a word by enclosing the word in double-quotes ("). A back-
slash (\) quotes the following character. A hash (#) starts a comment, which con-
tinues until the end of the line. There is no restriction on using the file or
call options within an options file.
SECURITY
pppd provides system administrators with sufficient access control that PPP access
to a server machine can be provided to legitimate users without fear of
compromising the security of the server or the network it’s on. This control is
provided through restrictions on which IP addresses the peer may use, based on its
authenticated identity (if any), and through restrictions on which options a non-
privileged user may use. Several of pppd’s options are privileged, in particular
those which permit potentially insecure configurations; these options are only
accepted in files which are under the control of the system administrator, or if
pppd is being run by root.
The default behaviour of pppd is to allow an unauthenticated peer to use a given IP
address only if the system does not already have a route to that IP address. For
example, a system with a permanent connection to the wider internet will normally
have a default route, and thus all peers will have to authenticate themselves in
order to set up a connection. On such a system, the auth option is the default.
On the other hand, a system where the PPP link is the only connection to the inter-
net will not normally have a default route, so the peer will be able to use almost
any IP address without authenticating itself.
As indicated above, some security-sensitive options are privileged, which means
that they may not be used by an ordinary non-privileged user running a setuid-root
pppd, either on the command line, in the user’s ~/.ppprc file, or in an options
file read using the file option. Privileged options may be used in
/etc/ppp/options file or in an options file read using the call option. If pppd is
being run by the root user, privileged options can be used without restriction.
When opening the device, pppd uses either the invoking user’s user ID or the root
UID (that is, 0), depending on whether the device name was specified by the user or
the system administrator. If the device name comes from a privileged source, that
is, /etc/ppp/options or an options file read using the call option, pppd uses full
root privileges when opening the device. Thus, by creating an appropriate file
under /etc/ppp/peers, the system administrator can allow users to establish a ppp
connection via a device which they would not normally have permission to access.
Otherwise pppd uses the invoking user’s real UID when opening the device.
AUTHENTICATION
Authentication is the process whereby one peer convinces the other of its identity.
This involves the first peer sending its name to the other, together with some kind
of secret information which could only come from the genuine authorized user of
that name. In such an exchange, we will call the first peer the "client" and the
other the "server". The client has a name by which it identifies itself to the
server, and the server also has a name by which it identifies itself to the client.
Generally the genuine client shares some secret (or password) with the server, and
authenticates itself by proving that it knows that secret. Very often, the names
used for authentication correspond to the internet hostnames of the peers, but this
is not essential.
At present, pppd supports three authentication protocols: the Password Authentica-
tion Protocol (PAP), Challenge Handshake Authentication Protocol (CHAP), and Exten-
sible Authentication Protocol (EAP). PAP involves the client sending its name and
a cleartext password to the server to authenticate itself. In contrast, the server
initiates the CHAP authentication exchange by sending a challenge to the client
(the challenge packet includes the server’s name). The client must respond with a
response which includes its name plus a hash value derived from the shared secret
and the challenge, in order to prove that it knows the secret. EAP supports CHAP-
style authentication, and also includes the SRP-SHA1 mechanism, which is resistant
to dictionary-based attacks and does not require a cleartext password on the server
side.
The PPP protocol, being symmetrical, allows both peers to require the other to
authenticate itself. In that case, two separate and independent authentication
exchanges will occur. The two exchanges could use different authentication proto-
cols, 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 authen-
ticating itself to other systems, as well as secrets for pppd to use when authenti-
cating other systems to itself.
Each line in a secrets file contains one secret. A given secret is specific to a
particular combination of client and server - it can only be used by that client to
authenticate itself to that server. Thus each line in a secrets file has at least
3 fields: the name of the client, the name of the server, and the secret. These
fields may be followed by a list of the IP addresses that the specified client may
use when connecting to the specified server.
A secrets file is parsed into words as for a options file, so the client name,
server name and secrets fields must each be one word, with any embedded spaces or
other special characters quoted or escaped. Note that case is significant in the
client and server names and in the secret.
If the secret starts with an ‘@’, what follows is assumed to be the name of a file
from which to read the secret. A "*" as the client or server name matches any
name. When selecting a secret, pppd takes the best match, i.e. the match with the
fewest wildcards.
Any following words on the same line are taken to be a list of acceptable IP
addresses for that client. If there are only 3 words on the line, or if the first
word is "-", then all IP addresses are disallowed. To allow any address, use "*".
A word starting with "!" indicates that the specified address is not acceptable.
An address may be followed by "/" and a number n, to indicate a whole subnet, i.e.
all addresses which have the same value in the most significant n bits. In this
form, the address may be followed by a plus sign ("+") to indicate that one address
from the subnet is authorized, based on the ppp network interface unit number in
use. In this case, the host part of the address will be set to the unit number
plus one.
Thus a secrets file contains both secrets for use in authenticating other hosts,
plus secrets which we use for authenticating ourselves to others. When pppd is
authenticating the peer (checking the peer’s identity), it chooses a secret with
the peer’s name in the first field and the name of the local system in the second
field. The name of the local system defaults to the hostname, with the domain name
appended if the domain option is used. This default can be overridden with the
name option, except when the usehostname option is used. (For EAP SRP-SHA1, see
the srp-entry(8) utility for generating proper validator entries to be used in the
"secret" field.)
When pppd is choosing a secret to use in authenticating itself to the peer, it
first determines what name it is going to use to identify itself to the peer. This
name can be specified by the user with the user option. If this option is not
used, the name defaults to the name of the local system, determined as described in
the previous paragraph. Then pppd looks for a secret with this name in the first
field and the peer’s name in the second field. Pppd will know the name of the peer
if CHAP or EAP authentication is being used, because the peer will have sent it in
the challenge packet. However, if PAP is being used, pppd will have to determine
the peer’s name from the options specified by the user. The user can specify the
peer’s name directly with the remotename option. Otherwise, if the remote IP
address was specified by a name (rather than in numeric form), that name will be
used as the peer’s name. Failing that, pppd will use the null string as the peer’s
name.
When authenticating the peer with PAP, the supplied password is first compared with
the secret from the secrets file. If the password doesn’t match the secret, the
password is encrypted using crypt() and checked against the secret again. Thus
secrets for authenticating the peer can be stored in encrypted form if desired. If
the papcrypt option is given, the first (unencrypted) comparison is omitted, for
better security.
Furthermore, if the login option was specified, the username and password are also
checked against the system password database. Thus, the system administrator can
set up the pap-secrets file to allow PPP access only to certain users, and to
restrict the set of IP addresses that each user can use. Typically, when using the
login option, the secret in /etc/ppp/pap-secrets would be "", which will match any
password supplied by the peer. This avoids the need to have the same secret in two
places.
Authentication must be satisfactorily completed before IPCP (or any other Network
Control Protocol) can be started. If the peer is required to authenticate itself,
and fails to do so, pppd will terminated the link (by closing LCP). If IPCP nego-
tiates 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 them-
selves 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 modifica-
tion 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 inter-
face. 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 perma-
nent, published ARP entry with the IP address of the remote host and the hardware
address of the network interface found.
When the demand option is used, the interface IP addresses have already been set at
the point when IPCP comes up. If pppd has not been able to negotiate the same
addresses that it used to configure the interface (for example when the peer is an
ISP that uses dynamic IP address assignment), pppd has to change the interface IP
addresses to the negotiated addresses. This may disrupt existing connections, and
the use of demand dialling with peers that do dynamic IP address assignment is not
recommended.
MULTILINK
Multilink PPP provides the capability to combine two or more PPP links between a
pair of machines into a single ‘bundle’, which appears as a single virtual PPP link
which has the combined bandwidth of the individual links. Currently, multilink PPP
is only supported under Linux.
Pppd detects that the link it is controlling is connected to the same peer as
another link using the peer’s endpoint discriminator and the authenticated identity
of the peer (if it authenticates itself). The endpoint discriminator is a block of
data which is hopefully unique for each peer. Several types of data can be used,
including locally-assigned strings of bytes, IP addresses, MAC addresses, randomly
strings of bytes, or E-164 phone numbers. The endpoint discriminator sent to the
peer by pppd can be set using the endpoint option.
In circumstances the peer may send no endpoint discriminator or a non-unique value.
The optional bundle option adds an extra string which is added to the peer’s end-
point 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 establish-
ment of multiple bundles between the local system and the peer. Pppd uses a TDB
database in /var/run/pppd.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. Currently, if the first pppd terminates (for example, because of a hangup or a
received signal) the bundle is destroyed.
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 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 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 facil-
ity.) See the syslog(8) documentation for details of where the syslog daemon will
write the messages. On most systems, the syslog daemon uses the /etc/syslog.conf
file to specify the destination(s) for syslog messages. You may need to edit that
file to suit.
The debug option causes the contents of all control packets sent or received to be
logged, that is, all LCP, PAP, CHAP, EAP, or IPCP packets. This can be useful if
the PPP negotiation does not succeed or if authentication fails. If debugging is
enabled at compile time, the debug option also causes other debugging messages to
be logged.
Debugging can also be enabled or disabled by sending a SIGUSR1 signal to the pppd
process. This signal acts as a toggle.
EXIT STATUS
The exit status of pppd is set to indicate whether any error was detected, or the
reason for the link being terminated. The values used are:
0 Pppd has detached, or otherwise the connection was successfully established
and terminated at the peer’s request.
1 An immediately fatal error of some kind occurred, such as an essential sys-
tem call failing, or running out of virtual memory.
2 An error was detected in processing the options given, such as two mutually
exclusive options being used.
3 Pppd is not setuid-root and the invoking user is not root.
4 The kernel does not support PPP, for example, the PPP kernel driver is not
included or cannot be loaded.
5 Pppd terminated because it was sent a SIGINT, SIGTERM or SIGHUP signal.
6 The serial port could not be locked.
7 The serial port could not be opened.
8 The connect script failed (returned a non-zero exit status).
9 The command specified as the argument to the pty option could not be run.
10 The PPP negotiation failed, that is, it didn’t reach the point where at
least one network protocol (e.g. IP) was running.
11 The peer system failed (or refused) to authenticate itself.
12 The link was established successfully and terminated because it was idle.
13 The link was established successfully and terminated because the connect
time limit was reached.
14 Callback was negotiated and an incoming call should arrive shortly.
15 The link was terminated because the peer is not responding to echo requests.
16 The link was terminated by the modem hanging up.
17 The PPP negotiation failed because serial loopback was detected.
18 The init script failed (returned a non-zero exit status).
19 We failed to authenticate ourselves to the peer.
SCRIPTS
Pppd invokes scripts at various stages in its processing which can be used to per-
form site-specific ancillary processing. These scripts are usually shell scripts,
but could be executable code files instead. Pppd does not wait for the scripts to
finish. 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 sys-
tem’s security. Pppd runs the scripts with standard input, output and error redi-
rected to /dev/null, and with an environment that is empty except for some environ-
ment variables that give information about the link. The environment variables
that pppd sets are:
DEVICE The name of the serial tty device being used.
IFNAME The name of the network interface being used.
IPLOCAL
The IP address for the local end of the link. This is only set when IPCP
has come up.
IPREMOTE
The IP address for the remote end of the link. This is only set when IPCP
has come up.
PEERNAME
The authenticated name of the peer. This is only set if the peer authenti-
cates 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 giv-
ing statistics for the connection:
CONNECT_TIME
The number of seconds from when the PPP negotiation started until the con-
nection was terminated.
BYTES_SENT
The number of bytes sent (at the level of the serial port) during the con-
nection.
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 sec-
ond 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-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 script. 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-proto-
col local-IPX-router-name remote-IPX-router-name ipparam pppd-pid
The local-IPX-routing-protocol and remote-IPX-routing-protocol field may be
one of the following:
NONE to indicate that there is no routing protocol
RIP to indicate that RIP/SAP should be used
NLSP to indicate that Novell NLSP should be used
RIP NLSP to indicate that both RIP/SAP and NLSP should be used
/etc/ppp/ipx-down
A program or script which is executed when the link is no longer available
for sending and receiving IPX packets. This script can be used for undoing
the effects of the /etc/ppp/ipx-up script. It is invoked in the same manner
and with the same parameters as the ipx-up script.
FILES
/var/run/pppn.pid (BSD or Linux), /etc/ppp/pppn.pid (others)
Process-ID for pppd process on ppp interface unit n.
/var/run/ppp-name.pid (BSD or Linux),
/etc/ppp/ppp-name.pid (others) Process-ID for pppd process for logical link
name (see the linkname option).
/etc/ppp/pap-secrets
Usernames, passwords and IP addresses for PAP authentication. This file
should be owned by root and not readable or writable by any other user.
Pppd will log a warning if this is not the case.
/etc/ppp/chap-secrets
Names, secrets and IP addresses for CHAP/MS-CHAP/MS-CHAPv2 authentication.
As for /etc/ppp/pap-secrets, this file should be owned by root and not read-
able 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 com-
mand-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 administra-
tor can create options files in this directory to permit non-privileged
users to dial out without requiring the peer to authenticate, but only to
certain trusted peers.
SEE ALSO
RFC1144
Jacobson, V. Compressing TCP/IP headers for low-speed serial links. Febru-
ary 1990.
RFC1321
Rivest, R. The MD5 Message-Digest Algorithm. April 1992.
RFC1332
McGregor, G. PPP Internet Protocol Control Protocol (IPCP). May 1992.
RFC1334
Lloyd, B.; Simpson, W.A. PPP authentication protocols. October 1992.
RFC1661
Simpson, W.A. The Point-to-Point Protocol (PPP). July 1994.
RFC1662
Simpson, W.A. PPP in HDLC-like Framing. July 1994.
RFC2284
Blunk, L.; Vollbrecht, J., PPP Extensible Authentication Protocol (EAP).
March 1998.
RFC2472
Haskin, D. IP Version 6 over PPP December 1998.
RFC2945
Wu, T., The SRP Authentication and Key Exchange System September 2000.
draft-ietf-pppext-eap-srp-03.txt
Carlson, J.; et al., EAP SRP-SHA1 Authentication Protocol. July 2001.
NOTES
Some limited degree of control can be exercised over a running pppd process by
sending it a signal from the list below.
SIGINT, SIGTERM
These signals cause pppd to terminate the link (by closing LCP), restore the
serial device settings, and exit.
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.
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 (Paul.Mackerras AT samba.org), based on earlier work by Drew Perkins,
Brad Clements, Karl Fox, Greg Christy, and Brad Parker.
PPPD(8)
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