pppd - Point-to-Point Protocol Daemon at Linux.org

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PPPD(8) System Manager's Manual 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 protocols besides IP, but such use is becoming increasingly rare.

FREQUENTLY USED OPTIONS
ttyname
Use the serial port called ttyname to communicate with the peer. If ttyname does not begin with a
slash (/), the string "/dev/" is prepended to ttyname to form the name of the device to open. If no
device name is given, or if the name of the terminal connected to the standard input is given, pppd
will use that terminal, and will not fork to put itself in the background. A value for this option
from a privileged source cannot be overridden by a non-privileged user.

speed An option that is a decimal number is taken as the desired baud rate for the serial device. On systems
such as 4.4BSD and NetBSD, any speed can be specified. Other systems (e.g. Linux, SunOS) only support
the commonly-used baud rates.

asyncmap map
This option sets the Async-Control-Character-Map (ACCM) for this end of the link. The ACCM is a set of
32 bits, one for each of the ASCII control characters with values from 0 to 31, where a 1 bit indicates
that the corresponding control character should not be used in PPP packets sent to this system. The
map is encoded as a hexadecimal number (without a leading 0x) where the least significant bit
(00000001) represents character 0 and the most significant bit (80000000) represents character 31.
Pppd will ask the peer to send these characters as a 2-byte escape sequence. If multiple asyncmap
options are given, the values are ORed together. If no asyncmap option is given, the default is zero,
so pppd will ask the peer not to escape any control characters. To escape transmitted characters, use
the escape option.

auth Require the peer to authenticate itself before allowing network packets to be sent or received. This
option is the default if the system has a default route. If neither this option nor the noauth option
is specified, pppd will only allow the peer to use IP addresses to which the system does not already
have a route.

call name
Read additional options from the file /etc/ppp/peers/name. This file may contain privileged options,
such as noauth, even if pppd is not being run by root. The name string may not begin with / or include
.. as a pathname component. The format of the options file is described below.

connect script
Usually there is something which needs to be done to prepare the link before the PPP protocol can be
started; for instance, with a dial-up modem, commands need to be sent to the modem to dial the appro‐
priate phone number. This option specifies an command for pppd to execute (by passing it to a shell)
before attempting to start PPP negotiation. The chat (8) program is often useful here, as it provides
a way to send arbitrary strings to a modem and respond to received characters. A value for this option
from a privileged source cannot be overridden by a non-privileged user.

crtscts
Specifies that pppd should set the serial port to use hardware flow control using the RTS and CTS sig‐

disconnect script
Execute the command specified by script, by passing it to a shell, after pppd has terminated the link.
This command could, for example, issue commands to the modem to cause it to hang up if hardware modem
control signals were not available. The disconnect script is not run if the modem has already hung up.
A value for this option from a privileged source cannot be overridden by a non-privileged user.

escape xx,yy,...
Specifies that certain characters should be escaped on transmission (regardless of whether the peer
requests them to be escaped with its async control character map). The characters to be escaped are
specified as a list of hex numbers separated by commas. Note that almost any character can be speci‐
fied for the escape option, unlike the asyncmap option which only allows control characters to be spec‐
ified. 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 nego‐
tiation, pppd will request that the kernel networking code send data packets of no more than n bytes
through the PPP network interface. Note that for the IPv6 protocol, the MTU must be at least 1280.

passive
Enables the "passive" option in the LCP. With this option, pppd will attempt to initiate a connection;
if no reply is received from the peer, pppd will then just wait passively for a valid LCP packet from
the peer, instead of exiting, as it would without this option.

OPTIONS
<local_IP_address>:<remote_IP_address>
Set the local and/or remote interface IP addresses. Either one may be omitted. The IP addresses can
be specified with a host name or in decimal dot notation (e.g. 150.234.56.78). The default local
address is the (first) IP address of the system (unless the noipdefault option is given). The remote
address will be obtained from the peer if not specified in any option. Thus, in simple cases, this
option is not required. If a local and/or remote IP address is specified with this option, pppd will
not accept a different value from the peer in the IPCP negotiation, unless the ipcp-accept-local and/or
ipcp-accept-remote options are given, respectively.

ipv6 <local_interface_identifier>,<remote_interface_identifier>
Set the local and/or remote 64-bit interface identifier. Either one may be omitted. The identifier must
be specified in standard ASCII notation of IPv6 addresses (e.g. ::dead:beef). If the ipv6cp-use-ipaddr
option is given, the local identifier is the local IPv4 address (see above). On systems which supports
a unique persistent id, such as EUI-48 derived from the Ethernet MAC address, ipv6cp-use-persistent
FIG_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 AUTHENTI‐
CATION section below).

allow-number number
Allow peers to connect from the given telephone number. A trailing `*' character will match all num‐
bers 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 com‐
pression dictionaries. Alternatively, a value of 0 for nr or nt disables compression in the corre‐
sponding direction. Use nobsdcomp or bsdcomp 0 to disable BSD-Compress compression entirely.

cdtrcts
Use a non-standard hardware flow control (i.e. DTR/CTS) to control the flow of data on the serial port.
If neither the crtscts, the nocrtscts, the cdtrcts nor the nocdtrcts option is given, the hardware flow
control setting for the serial port is left unchanged. Some serial ports (such as Macintosh serial
ports) lack a true RTS output. Such serial ports use this mode to implement true bi-directional flow
control. The sacrifice is that this flow control mode does not permit using DTR as a modem control
line.

chap-interval n
If this option is given, pppd will rechallenge the peer every n seconds.

chap-max-challenge n
Set the maximum number of CHAP challenge transmissions to n (default 10).

chap-restart n
Set the CHAP restart interval (retransmission timeout for challenges) to n seconds (default 3).

child-timeout n
When exiting, wait for up to n seconds for any child processes (such as the command specified with the
pty command) to exit before exiting. At the end of the timeout, pppd will send a SIGTERM signal to any
remaining child processes and exit. A value of 0 means no timeout, that is, pppd will wait until all
child processes have exited.

connect-delay n
Wait for up to n milliseconds after the connect script finishes for a valid PPP packet from the peer.
At the end of this time, or when a valid PPP packet is received from the peer, pppd will commence nego‐
tiation 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 facil‐
ity daemon and level debug. This information can be directed to a file by setting up /etc/syslog.conf
appropriately (see syslog.conf(5)).

be used for nr and nt; larger values give better compression but consume more kernel memory for com‐
pression dictionaries. Alternatively, a value of 0 for nr or nt disables compression in the corre‐
sponding direction. Use nodeflate or deflate 0 to disable Deflate compression entirely. (Note: pppd
requests Deflate compression in preference to BSD-Compress if the peer can do either.)

demand Initiate the link only on demand, i.e. when data traffic is present. With this option, the remote IP
address must be specified by the user on the command line or in an options file. Pppd will initially
configure the interface and enable it for IP traffic without connecting to the peer. When traffic is
available, pppd will connect to the peer and perform negotiation, authentication, etc. When this is
completed, pppd will commence passing data packets (i.e., IP packets) across the link.

The demand option implies the persist option. If this behaviour is not desired, use the nopersist
option after the demand option. The idle and holdoff options are also useful in conjunction with the
demand option.

domain d
Append the domain name d to the local host name for authentication purposes. For example, if gethost‐
name() returns the name porsche, but the fully qualified domain name is porsche.Quotron.COM, you could
specify domain Quotron.COM. Pppd would then use the name porsche.Quotron.COM for looking up secrets in
the secrets file, and as the default name to send to the peer when authenticating itself to the peer.
This option is privileged.

dryrun With the dryrun option, pppd will print out all the option values which have been set and then exit,
after parsing the command line and options files and checking the option values, but before initiating
the link. The option values are logged at level info, and also printed to standard output unless the
device on standard output is the device that pppd would be using to communicate with the peer.

dump With the dump option, pppd will print out all the option values which have been set. This option is
like the dryrun option except that pppd proceeds as normal rather than exiting.

enable-session
Enables session accounting via PAM or wtwp/wtmpx, as appropriate. When PAM is enabled, the PAM
"account" and "session" module stacks determine behavior, and are enabled for all PPP authentication
protocols. When PAM is disabled, wtmp/wtmpx entries are recorded regardless of whether the peer name
identifies a valid user on the local system, making peers visible in the last(1) log. This feature is
automatically enabled when the pppd login option is used. Session accounting is disabled by default.

endpoint <epdisc>
Sets the endpoint discriminator sent by the local machine to the peer during multilink negotiation to
<epdisc>. The default is to use the MAC address of the first ethernet interface on the system, if any,
otherwise the IPv4 address corresponding to the hostname, if any, provided it is not in the multicast
or locally-assigned IP address ranges, or the localhost address. The endpoint discriminator can be the
string null or of the form type:value, where type is a decimal number or one of the strings local, IP,
MAC, magic, or phone. The value is an IP address in dotted-decimal notation for the IP type, or a
string of bytes in hexadecimal, separated by periods or colons for the other types. For the MAC type,
the value may also be the name of an ethernet or similar network interface. This option is currently
only available under Linux.

eap-interval n
If this option is given and pppd authenticates the peer with EAP (i.e., is the server), pppd will
restart EAP authentication every n seconds. For EAP SRP-SHA1, see also the srp-interval option, which
enables lightweight rechallenge.

eap-max-rreq n

Set the maximum time to wait for the peer to send an EAP Request when acting as a client (authentica‐
tee). (Default is 20 seconds.)

hide-password
When logging the contents of PAP packets, this option causes pppd to exclude the password string from
the log. This is the default.

holdoff n
Specifies how many seconds to wait before re-initiating the link after it terminates. This option only
has any effect if the persist or demand option is used. The holdoff period is not applied if the link
was terminated because it was idle.

idle n Specifies that pppd should disconnect if the link is idle for n seconds. The link is idle when no data
packets (i.e. IP packets) are being sent or received. Note: it is not advisable to use this option
with the persist option without the demand option. If the active-filter option is given, data packets
which are rejected by the specified activity filter also count as the link being idle.

ipcp-accept-local
With this option, pppd will accept the peer's idea of our local IP address, even if the local IP
address was specified in an option.

ipcp-accept-remote
With this option, pppd will accept the peer's idea of its (remote) IP address, even if the remote IP
address was specified in an option.

ipcp-max-configure n
Set the maximum number of IPCP configure-request transmissions to n (default 10).

ipcp-max-failure n
Set the maximum number of IPCP configure-NAKs returned before starting to send configure-Rejects
instead to n (default 10).

ipcp-max-terminate n
Set the maximum number of IPCP terminate-request transmissions to n (default 3).

ipcp-restart n
Set the IPCP restart interval (retransmission timeout) to n seconds (default 3).

ipparam string
Provides an extra parameter to the ip-up, ip-pre-up and ip-down scripts. If this option is given, the
string supplied is given as the 6th parameter to those scripts.

ipv6cp-max-configure n
Set the maximum number of IPv6CP configure-request transmissions to n (default 10).

ipv6cp-max-failure n
Set the maximum number of IPv6CP configure-NAKs returned before starting to send configure-Rejects
instead to n (default 10).

ipv6cp-max-terminate n
Set the maximum number of IPv6CP terminate-request transmissions to n (default 3).

ipv6cp-restart n
Set the IPv6CP restart interval (retransmission timeout) to n seconds (default 3).
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 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-network
Accept the peer's NAK for the network number specified in the ipx-network option. If a network number
was specified, and non-zero, the default is to insist that the value be used. If you include this
option then you will permit the peer to override the entry of the node number.

ipxcp-accept-remote
Use the peer's network number specified in the configure request frame. If a node number was specified
for the peer and this option was not specified, the peer will be forced to use the value which you have
specified.

ipxcp-max-configure n
Set the maximum number of IPXCP configure request frames which the system will send to n. The default
is 10.

ipxcp-max-failure n
Set the maximum number of IPXCP NAK frames which the local system will send before it rejects the
options. The default value is 3.

ipxcp-max-terminate n
Set the maximum number 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 ker‐
nel 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-max-configure n
Set the maximum number of LCP configure-request transmissions to n (default 10).

lcp-max-failure n
Set the maximum number of LCP configure-NAKs returned before starting to send configure-Rejects instead
to n (default 10).

lcp-max-terminate n
Set the maximum number of LCP terminate-request transmissions to n (default 3).

lcp-restart n
Set the LCP restart interval (retransmission timeout) to n seconds (default 3).

linkname name
Sets the logical name of the link to name. Pppd will create a file named ppp-name.pid in /var/run (or
/etc/ppp on some systems) containing its process ID. This can be useful in determining which instance
of pppd is responsible for the link to a given peer system. This is a privileged option.

local Don't use the modem control lines. With this option, pppd will ignore the state of the CD (Carrier
Detect) signal from the modem and will not change the state of the DTR (Data Terminal Ready) signal.
This is the opposite of the modem option.

logfd n
Send log messages to file descriptor n. Pppd will send log messages to at most one file or file
descriptor (as well as sending the log messages to syslog), so this option and the logfile option are
mutually exclusive. The default is for pppd to send log messages to stdout (file descriptor 1), unless
the serial port is already open on stdout.

logfile filename
Append log messages to the file filename (as well as sending the log messages to syslog). The file is
opened with the privileges of the user who invoked pppd, in append mode.

login Use the system password database for authenticating the peer using PAP, and record the user in the sys‐
tem wtmp file. Note that the peer must have an entry in the /etc/ppp/pap-secrets file as well as the
system password database to be allowed access. See also the enable-session option.

maxconnect n
Terminate the connection when it has been available for network traffic for n seconds (i.e. n seconds
after the first network control protocol comes up).

maxfail n
Terminate after n consecutive failed connection attempts. A value of 0 means no limit. The default
value is 10.

modem Use the modem control lines. This option is the default. With this option, pppd will wait for the CD
(Carrier Detect) signal from the modem to be asserted when opening the serial device (unless a connect
script is specified), and it will drop the DTR (Data Terminal Ready) signal briefly when the connection
is terminated and before executing the connect script. On Ultrix, this option implies hardware flow
control, as for the crtscts option. This is the opposite of the local option.

mp Enables the use of PPP multilink; this is an alias for the `multilink' option. This option is cur‐
rently only available under Linux.

mppe-stateful
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 sup‐
ply 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 MULTI‐
LINK section below. This option is currently only available under Linux.

name name
Set the name of the local system for authentication purposes to name. This is a privileged option.
With this option, pppd will use lines in the secrets files which have name as the second field when
looking for a secret to use in authenticating the peer. In addition, unless overridden with the user
option, name will be used as the name to send to the peer when authenticating the local system to the
peer. (Note that pppd does not append the domain name to name.)

noaccomp
Disable Address/Control compression in both directions (send and receive).

noauth Do not require the peer to authenticate itself. This option is privileged.

nobsdcomp
Disables BSD-Compress compression; pppd will not request or agree to compress packets using the BSD-
Compress scheme.

noccp Disable CCP (Compression Control Protocol) negotiation. This option should only be required if the
peer is buggy and gets confused by requests from pppd for CCP negotiation.

nocrtscts
Disable hardware flow control (i.e. RTS/CTS) on the serial port. If neither the crtscts nor the
nocrtscts nor the cdtrcts nor the nocdtrcts option is given, the hardware flow control setting for the
serial port is left unchanged.

nocdtrcts
This option is a synonym for nocrtscts. Either of these options will disable both forms of hardware
flow control.

nodefaultroute
Disable the defaultroute option. The system administrator who wishes to prevent users from 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.

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 possi‐
ble) the local IP address from the hostname. With this option, the peer will have to supply the local
IP address during IPCP negotiation (unless it specified explicitly on the command line or in an options
file).

noipx Disable the IPXCP and IPX protocols. This option should only be required if the peer is buggy and gets
confused by requests from pppd for IPXCP negotiation.

noktune
Opposite of the ktune option; disables pppd from changing system settings.

nolock Opposite of the lock option; specifies that pppd should not create a UUCP-style lock file for the
serial device. This option is privileged.

nolog Do not send log messages to a file or file descriptor. This option cancels the logfd and logfile
options.

nomagic
Disable magic number negotiation. With this option, pppd cannot detect a looped-back line. This
option should only be needed if the peer is buggy.

nomp Disables the use of PPP multilink. This option is currently only available under Linux.

nomppe Disables MPPE (Microsoft Point to Point Encryption). This is the default.

nomppe-40
Disable 40-bit encryption with MPPE.

nomppe-128
Disable 128-bit encryption with MPPE.

nomppe-stateful
Disable MPPE stateful mode. This is the default.

nompshortseq
Disables the use of short (12-bit) sequence numbers in the PPP multilink protocol, forcing the use of
24-bit sequence numbers. This option is currently only available under Linux, and only has any effect
if multilink is enabled.

nomultilink
Disables the use of PPP multilink. This option is currently only available under Linux.

nopcomp
Disable protocol field compression negotiation in both the receive and the transmit direction.

nopersist
Exit once a connection has been made and terminated. This is the default unless the persist or demand
option has been specified.

nopredictor1
Do not accept or agree to Predictor-1 compression.

notty Normally, pppd requires a terminal device. With this option, pppd will allocate itself a pseudo-tty
master/slave pair and use the slave as its terminal device. Pppd will create a child process to act as
a `character shunt' to transfer characters between the pseudo-tty master and its standard input and
output. Thus pppd will transmit characters on its standard output and receive characters on its stan‐
dard 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 identi‐
cal to the secret from the /etc/ppp/pap-secrets file.

pap-max-authreq n
Set the maximum number of PAP authenticate-request transmissions to n (default 10).

pap-restart n
Set the PAP restart interval (retransmission timeout) to n seconds (default 3).

pap-timeout n
Set the maximum time that pppd will wait for the peer to authenticate itself with PAP to n seconds (0
means no limit).

pass-filter filter-expression
Specifies a packet filter to applied to data packets being sent or received to determine which packets
should be allowed to pass. Packets which are rejected by the filter are silently discarded. This
option can be used to prevent specific network daemons (such as routed) using up link bandwidth, or to
provide a very basic firewall capability. The filter-expression syntax is as described for tcpdump(1),
except that qualifiers which are inappropriate for a PPP link, such as ether and arp, are not permit‐
ted. 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 con‐
straints to incoming and outgoing packets using the inbound and outbound qualifiers. This option is
currently only available under Linux, and requires that the kernel was configured to include PPP fil‐
tering support (CONFIG_PPP_FILTER).

password password-string
Specifies the password to use for authenticating to the peer. Use of this option is discouraged, as
the password is likely to be visible to other users on the system (for example, by using ps(1)).

persist
Do not exit after a connection is terminated; instead try to reopen the connection. The maxfail option
still has an effect on persistent connections.

plugin filename
Load the shared library object file filename as a plugin. This is a privileged option. If filename
does not contain a slash (/), pppd will look in the /usr/lib/pppd/version directory for the plugin,

proxyarp
Add an entry to this system's ARP [Address Resolution Protocol] table with the IP address of the peer
and the Ethernet address of this system. This will have the effect of making the peer appear to other
systems to be on the local ethernet.

pty script
Specifies that the command script is to be used to communicate rather than a specific terminal device.
Pppd will allocate itself a pseudo-tty master/slave pair and use the slave as its terminal device. The
script will be run in a child process with the pseudo-tty master as its standard input and output. An
explicit device name may not be given if this option is used. (Note: if the record option is used in
conjunction with the pty option, the child process will have pipes on its standard input and output.)

receive-all
With this option, pppd will accept all control characters from the peer, including those marked in the
receive asyncmap. Without this option, pppd will discard those characters as specified in RFC1662.
This option should only be needed if the peer is buggy.

record filename
Specifies that pppd should record all characters sent and received to a file named filename. This file
is opened in append mode, using the user's user-ID and permissions. This option is implemented using a
pseudo-tty and a process to transfer characters between the pseudo-tty and the real serial device, so
it will increase the latency and CPU overhead of transferring data over the ppp interface. The charac‐
ters are stored in a tagged format with timestamps, which can be displayed in readable form using the
pppdump(8) program.

remotename name
Set the assumed name of the remote system for authentication purposes to name.

remotenumber number
Set the assumed telephone number of the remote system for authentication purposes to number.

refuse-chap
With this option, pppd will not agree to authenticate itself to the peer using CHAP.

refuse-mschap
With this option, pppd will not agree to authenticate itself to the peer using MS-CHAP.

refuse-mschap-v2
With this option, pppd will not agree to authenticate itself to the peer using MS-CHAPv2.

refuse-eap
With this option, pppd will not agree to authenticate itself to the peer using EAP.

refuse-pap
With this option, pppd will not agree to authenticate itself to the peer using PAP.

require-chap
Require the peer to authenticate itself using CHAP [Challenge Handshake Authentication Protocol]
authentication.

require-mppe
Require the use of MPPE (Microsoft Point to Point Encryption). This option disables all other compres‐
sion types. This option enables both 40-bit and 128-bit encryption. In order for MPPE to successfully

require-mschap-v2
Require the peer to authenticate itself using MS-CHAPv2 [Microsoft Challenge Handshake Authentication
Protocol, Version 2] authentication.

require-eap
Require the peer to authenticate itself using EAP [Extensible Authentication Protocol] authentication.

require-pap
Require the peer to authenticate itself using PAP [Password Authentication Protocol] authentication.

show-password
When logging the contents of PAP packets, this option causes pppd to show the password string in the
log message.

silent With this option, pppd will not transmit LCP packets to initiate a connection until a valid LCP packet
is received from the peer (as for the `passive' option with ancient versions of pppd).

srp-interval n
If this parameter is given and pppd uses EAP SRP-SHA1 to authenticate the peer (i.e., is the server),
then pppd will use the optional lightweight SRP rechallenge mechanism at intervals of n seconds. This
option is faster than eap-interval reauthentication because it uses a hash-based mechanism and does not
derive a new session key.

srp-pn-secret string
Set the long-term pseudonym-generating secret for the server. This value is optional and if set, needs
to be known at the server (authenticator) side only, and should be different for each server (or poll
of identical servers). It is used along with the current date to generate a key to encrypt and decrypt
the client's identity contained in the pseudonym.

srp-use-pseudonym
When operating as an EAP SRP-SHA1 client, attempt to use the pseudonym stored in ~/.ppp_pseudonym first
as the identity, and save in this file any pseudonym offered by the peer during authentication.

sync Use synchronous HDLC serial encoding instead of asynchronous. The device used by pppd with this option
must have sync support. Currently supports Microgate SyncLink adapters under Linux and FreeBSD 2.2.8
and later.

unit num
Sets the ppp unit number (for a ppp0 or ppp1 etc interface name) for outbound connections.

updetach
With this option, pppd will detach from its controlling terminal once it has successfully established
the ppp connection (to the point where the first network control protocol, usually the IP control pro‐
tocol, has come up).

usehostname
Enforce the use of the hostname (with domain name appended, if given) as the name of the local system
for authentication purposes (overrides the name option). This option is not normally needed since the
name option is privileged.

usepeerdns
Ask the peer for up to 2 DNS server addresses. The addresses supplied by the peer (if any) are passed
to the /etc/ppp/ip-up script in the environment variables DNS1 and DNS2, and the environment variable
connect script (if any) has completed. A value for this option from a privileged source cannot be
overridden by a non-privileged user.

xonxoff
Use software flow control (i.e. XON/XOFF) to control the flow of data on the serial port.

OPTIONS FILES
Options can be taken from files as well as the command line. Pppd reads options from the files
/etc/ppp/options, ~/.ppprc and /etc/ppp/options.ttyname (in that order) before processing the options on the
command line. (In fact, the command-line options are scanned to find the terminal name before the
options.ttyname file is read.) In forming the name of the options.ttyname file, the initial /dev/ is removed
from the terminal name, and any remaining / characters are replaced with dots.

An options file is parsed into a series of words, delimited by whitespace. Whitespace can be included in a
word by enclosing the word in double-quotes ("). A backslash (\) quotes the following character. A hash (#)
starts a comment, which continues until the end of the line. There is no restriction on using the file or
call options within an options file.

SECURITY
pppd provides system administrators with sufficient access control that PPP access to a server machine can be
provided to legitimate users without fear of compromising the security of the server or the network it's on.
This control is provided through restrictions on which IP addresses the peer may use, based on its authenti‐
cated identity (if any), and through restrictions on which options a non-privileged user may use. Several of
pppd's options are privileged, in particular those which permit potentially insecure configurations; these
options are only accepted in files which are under the control of the system administrator, or if pppd is
being run by root.

The default behaviour of pppd is to allow an unauthenticated peer to use a given IP address only if the system
does not already have a route to that IP address. For example, a system with a permanent connection to the
wider internet will normally have a default route, and thus all peers will have to authenticate themselves in
order to set up a connection. On such a system, the auth option is the default. On the other hand, a system
where the PPP link is the only connection to the internet will not normally have a default route, so the peer
will be able to use almost any IP address without authenticating itself.

As indicated above, some security-sensitive options are privileged, which means that they may not be used by
an ordinary non-privileged user running a setuid-root pppd, either on the command line, in the user's ~/.ppprc
file, or in an options file read using the file option. Privileged options may be used in /etc/ppp/options
file or in an options file read using the call option. If pppd is being run by the root user, privileged
options can be used without restriction.

When opening the device, pppd uses either the invoking user's user ID or the root UID (that is, 0), depending
on whether the device name was specified by the user or the system administrator. If the device name comes
from a privileged source, that is, /etc/ppp/options or an options file read using the call option, pppd uses
full root privileges when opening the device. Thus, by creating an appropriate file under /etc/ppp/peers, the
system administrator can allow users to establish a ppp connection via a device which they would not normally
have permission to access. Otherwise pppd uses the invoking user's real UID when opening the device.

AUTHENTICATION
Authentication is the process whereby one peer convinces the other of its identity. This involves the first
peer sending its name to the other, together with some kind of secret information which could only come from
the genuine authorized user of that name. In such an exchange, we will call the first peer the "client" and
the other the "server". The client has a name by which it identifies itself to the server, and the server
also has a name by which it identifies itself to the client. Generally the genuine client shares some secret
(or password) with the server, and authenticates itself by proving that it knows that secret. Very often, the
case, two separate and independent authentication exchanges will occur. The two exchanges could use different
authentication protocols, and in principle, different names could be used in the two exchanges.

The default behaviour of pppd is to agree to authenticate if requested, and to not require authentication from
the peer. However, pppd will not agree to authenticate itself with a particular protocol if it has no secrets
which could be used to do so.

Pppd stores secrets for use in authentication in secrets files (/etc/ppp/pap-secrets for PAP,
/etc/ppp/chap-secrets for CHAP, MS-CHAP, MS-CHAPv2, and EAP MD5-Challenge, and /etc/ppp/srp-secrets for EAP
SRP-SHA1). All secrets files have the same format. The secrets files can contain secrets for pppd to use in
authenticating itself to other systems, as well as secrets for pppd to use when authenticating other systems
to itself.

Each line in a secrets file contains one secret. A given secret is specific to a particular combination of
client and server - it can only be used by that client to authenticate itself to that server. Thus each line
in a secrets file has at least 3 fields: the name of the client, the name of the server, and the secret.
These fields may be followed by a list of the IP addresses that the specified client may use when connecting
to the specified server.

A secrets file is parsed into words as for a options file, so the client name, server name and secrets fields
must each be one word, with any embedded spaces or other special characters quoted or escaped. Note that case
is significant in the client and server names and in the secret.

If the secret starts with an `@', what follows is assumed to be the name of a file from which to read the
secret. A "*" as the client or server name matches any name. When selecting a secret, pppd takes the best
match, i.e. the match with the fewest wildcards.

Any following words on the same line are taken to be a list of acceptable IP addresses for that client. If
there are only 3 words on the line, or if the first word is "-", then all IP addresses are disallowed. To
allow any address, use "*". A word starting with "!" indicates that the specified address is not acceptable.
An address may be followed by "/" and a number n, to indicate a whole subnet, i.e. all addresses which have
the same value in the most significant n bits. In this form, the address may be followed by a plus sign ("+")
to indicate that one address from the subnet is authorized, based on the ppp network interface unit number in
use. In this case, the host part of the address will be set to the unit number plus one.

Thus a secrets file contains both secrets for use in authenticating other hosts, plus secrets which we use for
authenticating ourselves to others. When pppd is authenticating the peer (checking the peer's identity), it
chooses a secret with the peer's name in the first field and the name of the local system in the second field.
The name of the local system defaults to the hostname, with the domain name appended if the domain option is
used. This default can be overridden with the name option, except when the usehostname option is used. (For
EAP SRP-SHA1, see the srp-entry(8) utility for generating proper validator entries to be used in the "secret"
field.)

When pppd is choosing a secret to use in authenticating itself to the peer, it first determines what name it
is going to use to identify itself to the peer. This name can be specified by the user with the user option.
If this option is not used, the name defaults to the name of the local system, determined as described in the
previous paragraph. Then pppd looks for a secret with this name in the first field and the peer's name in the
second field. Pppd will know the name of the peer if CHAP or EAP authentication is being used, because the
peer will have sent it in the challenge packet. However, if PAP is being used, pppd will have to determine
the peer's name from the options specified by the user. The user can specify the peer's name directly with
the remotename option. Otherwise, if the remote IP address was specified by a name (rather than in numeric
form), that name will be used as the peer's name. Failing that, pppd will use the null string as the peer's
name.

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 speci‐
fies 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 fur‐
ther modification to routing tables and/or ARP (Address Resolution Protocol) tables. In most cases the
defaultroute and/or proxyarp options are sufficient for this, but in some cases further intervention is
required. The /etc/ppp/ip-up script can be used for this.

Sometimes it is desirable to add a default route through the remote host, as in the case of a machine whose
only connection to the Internet is through the ppp interface. The defaultroute option causes pppd to create
such a default route when IPCP comes up, and delete it when the link is terminated.

In some cases it is desirable to use proxy ARP, for example on a server machine connected to a LAN, in order
to allow other hosts to communicate with the remote host. The proxyarp option causes pppd to look for a net‐
work interface on the same subnet as the remote host (an interface supporting broadcast and ARP, which is up
and not a point-to-point or loopback interface). If found, pppd creates a permanent, published ARP entry with
the IP address of the remote host and the hardware address of the network interface found.

When the demand option is used, the interface IP addresses have already been set at the point when IPCP comes
up. If pppd has not been able to negotiate the same addresses that it used to configure the interface (for
example when the peer is an ISP that uses dynamic IP address assignment), pppd has to change the interface IP
addresses to the negotiated addresses. This may disrupt existing connections, and the use of demand dialling
with peers that do dynamic IP address assignment is not recommended.

MULTILINK
Multilink PPP provides the capability to combine two or more PPP links between a pair of machines into a sin‐
gle `bundle', which appears as a single virtual PPP link which has the combined bandwidth of the individual
links. Currently, multilink PPP is only supported under Linux.

Pppd detects that the link it is controlling is connected to the same peer as another link using the peer's
endpoint discriminator and the authenticated identity of the peer (if it authenticates itself). The endpoint
discriminator is a block of data which is hopefully unique for each peer. Several types of data can be used,
including locally-assigned strings of bytes, IP addresses, MAC addresses, randomly strings of bytes, or E-164
phone numbers. The endpoint discriminator sent to the peer by pppd can be set using the endpoint option.

In some circumstances the peer may send no endpoint discriminator or a non-unique value. The bundle option
adds an extra string which is added to the peer's endpoint discriminator and authenticated identity when
matching up links to be joined together in a bundle. The bundle option can also be used to allow the estab‐
lishment of multiple bundles between the local system and the peer. Pppd uses a TDB database in
/var/run/pppd2.tdb to match up links.

Assuming that multilink is enabled and the peer is willing to negotiate multilink, then when pppd is invoked
to bring up the first link to the peer, it will detect that no other link is connected to the peer and create

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 cre‐
ate an entry in /etc/ppp/pap-secrets, /etc/ppp/chap-secrets, or /etc/ppp/srp-secrets (depending on which
authentication method the PPP implementation on the user's machine supports), so that the user's machine can
authenticate itself. For example, if Joe has a machine called "joespc" that is to be allowed to dial in to
the machine called "server" and use the IP address joespc.my.net, you would add an entry like this to
/etc/ppp/pap-secrets or /etc/ppp/chap-secrets:

joespc server "joe's secret" joespc.my.net

(See srp-entry(8) for a means to generate the server's entry when SRP-SHA1 is in use.) Alternatively, you can
create a username called (for example) "ppp", whose login shell is pppd and whose home directory is /etc/ppp.
Options to be used when pppd is run this way can be put in /etc/ppp/.ppprc.

If your serial connection is any more complicated than a piece of wire, you may need to arrange for some con‐
trol characters to be escaped. In particular, it is often useful to escape XON (^Q) and XOFF (^S), using
PAP, CHAP, EAP, or IPCP packets. This can be useful if the PPP negotiation does not succeed or if authentica‐
tion fails. If debugging is enabled at compile time, the debug option also causes other debugging messages to
be logged.

Debugging can also be enabled or disabled by sending a SIGUSR1 signal to the pppd process. This signal acts
as a toggle.

EXIT STATUS
The exit status of pppd is set to indicate whether any error was detected, or the reason for the link being
terminated. The values used are:

0 Pppd has detached, or otherwise the connection was successfully established and terminated at the
peer's request.

1 An immediately fatal error of some kind occurred, such as an essential system call failing, or running
out of virtual memory.

2 An error was detected in processing the options given, such as two mutually exclusive options being
used.

3 Pppd is not setuid-root and the invoking user is not root.

4 The kernel does not support PPP, for example, the PPP kernel driver is not included or cannot be
loaded.

5 Pppd terminated because it was sent a SIGINT, SIGTERM or SIGHUP signal.

6 The serial port could not be locked.

7 The serial port could not be opened.

8 The connect script failed (returned a non-zero exit status).

9 The command specified as the argument to the pty option could not be run.

10 The PPP negotiation failed, that is, it didn't reach the point where at least one network protocol
(e.g. IP) was running.

11 The peer system failed (or refused) to authenticate itself.

12 The link was established successfully and terminated because it was idle.

13 The link was established successfully and terminated because the connect time limit was reached.

14 Callback was negotiated and an incoming call should arrive shortly.

15 The link was terminated because the peer is not responding to echo requests.

16 The link was terminated by the modem hanging up.

17 The PPP negotiation failed because serial loopback was detected.

18 The init script failed (returned a non-zero exit status).

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 con‐
nection:

CONNECT_TIME
The number of seconds from when the PPP negotiation started until the connection was terminated.

BYTES_SENT
The number of bytes sent (at the level of the serial port) during the connection.

BYTES_RCVD
The number of bytes received (at the level of the serial port) during the connection.

LINKNAME
The logical name of the link, set with the linkname option.

DNS1 If the peer supplies DNS server addresses, this variable is set to the first DNS server address sup‐
plied.

DNS2 If the peer supplies DNS server addresses, this variable is set to the second DNS server address sup‐
plied.

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

(that is, IPCP has come up). It is executed with the parameters

interface-name tty-device speed local-IP-address remote-IP-address ipparam

/etc/ppp/ip-down
A program or script which is executed when the link is no longer available for sending and receiving IP
packets. This script can be used for undoing the effects of the /etc/ppp/ip-up and /etc/ppp/ip-pre-up
scripts. It is invoked in the same manner and with the same parameters as the ip-up script.

/etc/ppp/ipv6-up
Like /etc/ppp/ip-up, except that it is executed when the link is available for sending and receiving
IPv6 packets. It is executed with the parameters

interface-name tty-device speed local-link-local-address remote-link-local-address ipparam

/etc/ppp/ipv6-down
Similar to /etc/ppp/ip-down, but it is executed when IPv6 packets can no longer be transmitted on the
link. It is executed with the same parameters as the ipv6-up script.

/etc/ppp/ipx-up
A program or script which is executed when the link is available for sending and receiving IPX packets
(that is, IPXCP has come up). It is executed with the parameters

interface-name tty-device speed network-number local-IPX-node-address remote-IPX-node-address
local-IPX-routing-protocol remote-IPX-routing-protocol local-IPX-router-name remote-IPX-router-name
ipparam pppd-pid

The local-IPX-routing-protocol and remote-IPX-routing-protocol field may be one of the following:

NONE to indicate that there is no routing protocol
RIP to indicate that RIP/SAP should be used
NLSP to indicate that Novell NLSP should be used
RIP NLSP to indicate that both RIP/SAP and NLSP should be used

/etc/ppp/ipx-down
A program or script which is executed when the link is no longer available for sending and receiving
IPX packets. This script can be used for undoing the effects of the /etc/ppp/ipx-up script. It is
invoked in the same manner and with the same parameters as the ipx-up script.

FILES
/var/run/pppn.pid (BSD or Linux), /etc/ppp/pppn.pid (others)
Process-ID for pppd process on ppp interface unit n.

/var/run/ppp-name.pid (BSD or Linux),
/etc/ppp/ppp-name.pid (others) Process-ID for pppd process for logical link name (see the linkname
option).

/var/run/pppd2.tdb
Database containing information about pppd processes, interfaces and links, used for matching links to
bundles in multilink operation. May be examined by external programs to obtain information about run‐
ning pppd instances, the interfaces and devices they are using, IP address assignments, etc.
/etc/ppp/pap-secrets Usernames, passwords and IP addresses for PAP authentication. This file should be
owned by root and not readable or writable by any other user. Pppd will log a warning if this is not
the case.
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.