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PPPD(8) Unix Programmer's Manual PPPD(8)
NAME
pppd - Point to Point Protocol daemon
SYNOPSIS
pppd [ tty_name ] [ speed ] [ options ]
DESCRIPTION
The Point-to-Point Protocol (PPP) provides a method for transmitting
datagrams over serial point-to-point links. PPP is composed of three
parts: a method for encapsulating datagrams over serial links, an
extensible Link Control Protocol (LCP), and a family of Network Control
Protocols (NCP) for establishing and configuring different network-layer
protocols.
The encapsulation scheme is provided by driver code in the kernel. Pppd
provides the basic LCP, authentication support, and an NCP for
establishing and configuring the Internet Protocol (IP) (called the IP
Control Protocol, IPCP).
FREQUENTLY USED OPTIONS
<tty_name>
Communicate over the named device. The string "/dev/" is prepended
if necessary. 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.
This option is privileged if the noauth option is used.
<speed>
Set the baud rate to <speed> (a decimal number). On systems such as
4.4BSD and NetBSD, any speed can be specified. Other systems (e.g.
SunOS) allow only a limited set of speeds.
asyncmap <map>
Set the async character map to <map>. This map describes which
control characters cannot be successfully received over the serial
line. Pppd will ask the peer to send these characters as a 2-byte
escape sequence. The argument is a 32 bit hex number with each bit
representing a character to escape. Bit 0 (00000001) represents the
character 0x00; bit 31 (80000000) represents the character 0x1f or
^_. If multiple asyncmap options are given, the values are ORed
together. If no asyncmap option is given, no async character map
will be negotiated for the receive direction; the peer should then
escape all 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.
call name
Read 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.
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PPPD(8) Unix Programmer's Manual PPPD(8)
connect script
Use the executable or shell command specified by script to set up
the serial line. This script would typically use the chat(8)
program to dial the modem and start the remote ppp session. This
option is privileged if the noauth option is used.
crtscts
Use hardware flow control (i.e. RTS/CTS) to control the flow of data
on the serial port. If neither the crtscts nor the nocrtscts option
is given, the hardware flow control setting for the serial port is
left unchanged.
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
Run the executable or shell command specified by script after pppd
has terminated the link. This script 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. This option is privileged if
the noauth option is used.
escape xx,yy,...
Specifies that certain characters should be escaped on transmission
(regardless of whether the peer requests them to be escaped with its
async control character map). The characters to be escaped are
specified as a list of hex numbers separated by commas. Note that
almost any character can be specified for the escape option, unlike
the asyncmap option which only allows control characters to be
specified. The characters which may not be escaped are those with
hex values 0x20 - 0x3f or 0x5e.
file name
Read options from file name (the format is described below). The
file must be readable by the user who has invoked pppd.
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 minimum MRU value
is 128. The default MRU value is 1500. A value of 296 is
recommended for slow links (40 bytes for TCP/IP header + 256 bytes
of data).
mtu n
Set the MTU [Maximum Transmit Unit] value to n. Unless the peer
requests a smaller value via MRU negotiation, pppd will request that
the kernel networking code send data packets of no more than n bytes
through the PPP network interface.
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PPPD(8) Unix Programmer's Manual PPPD(8)
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.
bsdcomp nr,nt
Request that the peer compress packets that it sends, using the BSD-
Compress scheme, with a maximum code size of nr bits, and agree to
compress packets sent to the peer with a maximum code size of nt
bits. If nt is not specified, it defaults to the value given for
nr. Values in the range 9 to 15 may be used for nr and nt; larger
values give better compression but consume more kernel memory for
compression dictionaries. Alternatively, a value of 0 for nr or nt
disables compression in the corresponding direction. Use nobsdcomp
or bsdcomp 0 to disable BSD-Compress compression entirely.
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).
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.
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PPPD(8) Unix Programmer's Manual PPPD(8)
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 8 to 15 may be used for nr and nt;
larger values give better compression but consume more kernel memory
for compression dictionaries. Alternatively, a value of 0 for nr or
nt disables compression in the corresponding direction. Use
nodeflate or deflate 0 to disable Deflate compression entirely.
(Note: pppd requests Deflate compression in preference to BSD-
Compress if the peer can do either.)
demand
Initiate the link only on demand, i.e. when data traffic is present.
With this option, the remote IP address 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 conjuction with the
demand option.
domain d
Append the domain name d to the local host name for authentication
purposes. For example, if gethostname() returns the name porsche,
but the fully qualified domain name is porsche.Quotron.COM, you
could specify domain Quotron.COM. Pppd would then use the name
porsche.Quotron.COM for looking up secrets in the secrets file, and
as the default name to send to the peer when authenticating itself
to the peer. This option is privileged.
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.
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PPPD(8) Unix Programmer's Manual PPPD(8)
ipx Enable the IPXCP and IPX protocols. Under Linux, this is the
default condition if your kernel supports IPX. This option is
presently only supported under Linux.
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.
ipx-network n
Set the IPX network number in the IPXCP configure request frame to
n, a hexadecimal number (without a leading 0x). There is no valid
default. If this option is not 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.
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PPPD(8) Unix Programmer's Manual PPPD(8)
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 permit the peer to override the entry of the
node number.
ipxcp-accept-remote
Use the peer's network number specified in the configure request
frame. If a node number was specified for the peer and this option
was not specified, the peer will be forced to use the value which
you have specified.
ipxcp-max-configure n
Set the maximum number of IPXCP configure request frames which the
system will send to n. The default is 10.
ipxcp-max-failure n
Set the maximum number of IPXCP NAK frames which the local system
will send before it rejects the options. The default value is 3.
ipxcp-max-terminate n
Set the maximum nuber of IPXCP terminate request frames before the
local system considers that the peer is not listening to them. The
default value is 3.
kdebug n
Enable debugging code in the kernel-level PPP driver. The argument
n is a number which is the sum of the following values: 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.
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.
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PPPD(8) Unix Programmer's Manual PPPD(8)
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).
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.
login
Use the system password database for authenticating the peer using
PAP, and record the user in the system wtmp file. Note that if the
/etc/ppp/pap-secrets file exists, the peer must have an entry in
that file as well as the system password database to be allowed
access.
maxconnect n
Terminate the connection after n seconds.
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.
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.)
7
PPPD(8) Unix Programmer's Manual PPPD(8)
name name
Set the name of the local system for authentication purposes to
name. This is a privileged option. With this option, pppd will use
lines in the secrets files which have name as the second field when
looking for a secret to use in authenticating the peer. In
addition, unless overridden with the user option, name will be used
as the name to send to the peer when authenticating the local system
to the peer. (Note that pppd does not append the domain name to
name.)
netmask n
Set the interface netmask to n, a 32 bit netmask in "decimal dot"
notation (e.g. 255.255.255.0). If this option is given, the value
specified is ORed with the default netmask. The default netmask is
chosen based on the negotiated remote IP address; it is the
appropriate network mask for the class of the remote IP address,
ORed with the netmasks for any non point-to-point network interfaces
in the system which are on the same network.
noaccomp
Disable Address/Control compression in both directions (send and
receive).
noauth
Do not require the peer to authenticate itself. This option is
privileged if the auth option is specified in /etc/ppp/options.
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 option is given, the hardware
flow control setting for the serial port is left unchanged.
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.
8
PPPD(8) Unix Programmer's Manual PPPD(8)
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.
noipdefault
Disables the default behaviour when no local IP address is
specified, which is to determine (if possible) the local IP address
from the hostname. With this option, the peer will have to supply
the local IP address during IPCP negotiation (unless it specified
explicitly on the command line or in an options file).
noipx
Disable the IPXCP and IPX protocols. This option should only be
required if the peer is buggy and gets confused by requests from
pppd for IPXCP negotiation.
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.
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 comprssion.
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.
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).
9
PPPD(8) Unix Programmer's Manual PPPD(8)
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).
persist
Do not exit after a connection is terminated; instead try to reopen
the connection.
predictor1
Request that the peer compress frames that it sends using Predictor-
1 compression, and agree to compress transmitted frames with
Predictor-1 if requested. This option has no effect unless the
kernel driver supports Predictor-1 compression.
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.
remotename name
Set the assumed name of the remote system for authentication
purposes to name.
refuse-chap
With this option, pppd will not agree to authenticate itself to the
peer using CHAP.
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-pap
Require the peer to authenticate itself using PAP [Password
Authentication Protocol] authentication.
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).
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).
10
PPPD(8) Unix Programmer's Manual PPPD(8)
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. This option is privileged if the noauth option is used.
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 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.
PRIVILEGED OPTIONS
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.
The normal way that pppd should be set up is to have the auth option in
the /etc/ppp/options file. (This may become the default in later
releases.) If users wish to use pppd to dial out to a peer which will
refuse to authenticate itself (such as an internet service provider), the
system administrator should create an options file under /etc/ppp/peers
containing the noauth option, the name of the serial port to use, and the
connect option (if required), plus any other appropriate options. In
this way, pppd can be set up to allow non-privileged users to make
unauthenticated connections only to trusted peers.
11
PPPD(8) Unix Programmer's Manual PPPD(8)
AUTHENTICATION
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. In part this is provided by the /etc/ppp/options file, where
the administrator can place options to restrict the ways in which pppd
can be used, and in part by the PAP and CHAP secrets files, where the
administrator can restrict the set of IP addresses which individual users
may use.
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.
Authentication is based on secrets, which are selected from secrets files
(/etc/ppp/pap-secrets for PAP, /etc/ppp/chap-secrets for CHAP). Both
secrets files have the same format, and both can store secrets for
several combinations of server (authenticating peer) and client (peer
being authenticated). Note that pppd can be both a server and client,
and that different protocols can be used in the two directions if
desired.
A secrets file is parsed into words as for a options file. A secret is
specified by a line containing at least 3 words, in the order client
name, server name, secret. 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, it is assumed that any IP address is OK; to
disallow all IP addresses, 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. 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.
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 column and the name of
the local system in the second column. 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
(unless the usehostname option is used.)
When pppd is choosing a secret to use in authenticating itself to the
peer, it looks for a secret with the local name in the first column and
the name of the remote system in the second column. The local name is
determined as described in the previous paragraph, except that it may be
overridden with the user option. The remote name will have been received
from the peer if CHAP authentication is being used. However, with PAP,
pppd does not know the remote name at the time when it has to look for
the secret. In this case, it will use the value given for the remotename
12
PPPD(8) Unix Programmer's Manual PPPD(8)
option if specified. Failing that, if the remote IP address was given as
a name (rather than in numeric form), it will use that name. Failing
that, it will use the empty string.
When authenticating the peer with PAP, a secret of "" matches any
password supplied by the peer. 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 the papcrypt option is given, the first (unencrypted)
comparison is omitted, for better security.
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 "", to avoid the need to have the same secret in two
places.
Authentication must be satisfactorily completed before IPCP (or any other
Network Control Protocol) can be started. If the peer is required to
authenticate itself, and fails to do so, pppd will terminated the link
(by closing LCP). If IPCP negotiates an unacceptable IP address for the
remote host, IPCP will be closed. IP packets can only be sent or
received when IPCP is open.
In some cases it is desirable to allow some hosts which can't
authenticate themselves to connect and use one of a restricted set of IP
addresses, even when the local host generally requires authentication.
If the peer refuses to authenticate itself when requested, pppd takes
that as equivalent to authenticating with PAP using the empty string for
the username and password. Thus, by adding a line to the pap-secrets
file which specifies the empty string for the client and password, it is
possible to allow restricted access to hosts which refuse to authenticate
themselves.
ROUTING
When IPCP negotiation is completed successfully, pppd will inform the
kernel of the local and remote IP addresses for the ppp interface. This
is sufficient to create a host route to the remote end of the link, which
will enable the peers to exchange IP packets. Communication with other
machines generally requires further modification to routing tables and/or
ARP (Address Resolution Protocol) tables. In most cases the defaultroute
and/or proxyarp options are sufficient for this, but in some cases
further intervention is required. The /etc/ppp/ip-up script can be used
for this.
Sometimes it is desirable to add a default route through the remote host,
as in the case of a machine whose only connection to the Internet is
through the ppp interface. The defaultroute option causes pppd to create
such a default route when IPCP comes up, and delete it when the link is
terminated.
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In some cases it is desirable to use proxy ARP, for example on a server
machine connected to a LAN, in order to allow other hosts to communicate
with the remote host. The proxyarp option causes pppd to look for a
network interface on the same subnet as the remote host (an interface
supporting broadcast and ARP, which is up and not a point-to-point or
loopback interface). If found, pppd creates a permanent, published ARP
entry with the IP address of the remote host and the hardware address of
the network interface found.
EXAMPLES
In the simplest case, you can connect the serial ports of two machines
and issue a command like
pppd /dev/ttya 9600 passive
to each machine, assuming there is no getty running on the serial ports.
If one machine has a getty running, you can use kermit or tip on the
other machine to log in to the first machine and issue a command like
pppd passive
Then exit from the communications program (making sure the connection
isn't dropped), and issue a command like
pppd /dev/ttya 9600
The process of logging in to the other machine and starting pppd can be
automated by using the connect option to run chat, for example:
pppd /dev/ttya 38400 connect 'chat "" "" "login:" "username"
"Password:" "password" "% " "exec pppd passive"'
(Note however that running chat like this will leave the password visible
in the parameter list of pppd and chat.)
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 overriden by recompiling pppd with the macro LOG_PPP defined as
the desired facility.) In order to see the error and debug messages, you
will need to edit your /etc/syslog.conf file to direct the messages to
the desired output device or file.
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PPPD(8) Unix Programmer's Manual PPPD(8)
The debug option causes the contents of all control packets sent or
received to be logged, that is, all LCP, PAP, CHAP 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.
FILES
/var/run/pppn.pid (BSD or Linux), /etc/ppp/pppn.pid (others)
Process-ID for pppd process on ppp interface unit n.
/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
and with its standard input, output and error redirected to
/dev/null. This program or script is executed with the real and
effective user-IDs set to root, and with an empty environment.
(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
and with its standard input, output and error streams redirected to
/dev/null.
This program or script is executed with the real and effective user-
IDs set to root. This is so that it can be used to manipulate
routes, run privileged daemons (e.g. sendmail), etc. Be careful
that the contents of the /etc/ppp/ip-up and /etc/ppp/ip-down scripts
do not compromise your system's security.
This program or script is executed with an empty environment, so you
must either specify a PATH or use full pathnames.
/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
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PPPD(8) Unix Programmer's Manual PPPD(8)
invoked in the same manner and with the same parameters as the ip-up
script, and the same security considerations apply.
/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
and with its standard input, output and error streams redirected to
/dev/null.
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
This program or script is executed with the real and effective user-
IDs set to root, and with an empty environment. This is so that it
can be used to manipulate routes, run privileged daemons (e.g.
ripd), etc. Be careful that the contents of the /etc/ppp/ipx-up and
/etc/ppp/ipx-down scripts do not compromise your system's security.
/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, and the same security considerations apply.
/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 authentication. As for
/etc/ppp/pap-secrets, this file should be owned by root and not
readable or writable by any other user. Pppd will log a warning if
this is not the case.
/etc/ppp/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.
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/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.
SEE ALSO
RFC1144
Jacobson, V. Compressing TCP/IP headers for low-speed serial links.
February 1990.
RFC1321
Rivest, R. The MD5 Message-Digest Algorithm. April 1992.
RFC1332
McGregor, G. PPP Internet Protocol Control Protocol (IPCP). May
1992.
RFC1334
Lloyd, B.; Simpson, W.A. PPP authentication protocols. October
1992.
RFC1661
Simpson, W.A. The Point-to-Point Protocol (PPP). July 1994.
RFC1662
Simpson, W.A. PPP in HDLC-like Framing. July 1994.
NOTES
The following signals have the specified effect when sent to pppd.
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.)
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AUTHORS
Paul Mackerras (Paul.Mackerras@cs.anu.edu.au), based on earlier work by
Drew Perkins, Brad Clements, Karl Fox, Greg Christy, and Brad Parker.
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