pppd(8) - Linux man page
DISCLAIMER
This page is derived from the Linux pppd manual page. Several sections
have been omitted since they are not applicable to the implementation of
pppd in the Trimble NetRS product. For the complete page, consult
any Linux system or look on the web.
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).
Note that on the Trimble NetRS, the command line invocation is
done automatically when the PPP Dialout function is activated. The
tty_name, speed and options are determined from the user defined
specifications.
FREQUENTLY USED OPTIONS
- <tty_name>
- Communicate over the named device.
On the Trimble NetRS, this value is automatically filled in, based on
which serial port the PPP Dialout function is activated.
- <speed>
- Set the baud rate to <speed> (a decimal number).
On the Trimble NetRS, this value is automatically filled in, based on
the baud rate selected when the PPP Dialout function is activated.
- 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. 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.
On the Trimble NetRS, the noauth option is always forced.
- call name
- Not available in the Trimble NetRS.
- connect script
- Not available in the Trimble NetRS.
- crtscts
- Use hardware flow control (i.e. RTS/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 unidirectional flow control. The serial port will suspend
transmission when requested by the modem (via CTS) but will be
unable to request the modem stop sending to the computer. This mode
retains the ability to use DTR as a modem control line.
- defaultroute
- Add a default route to the system routing tables, using the
peer as the gateway, when IPCP negotiation is successfully
completed. This entry is removed when the PPP connection is broken.
This option is privileged if the nodefaultroute option has
been specified.
- disconnect script
- Not available in the Trimble NetRS.
- 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
- Not available in the Trimble NetRS.
- init script
- Not available in the Trimble NetRS.
- lock
- Specifies that pppd should create a UUCP-style lock file for
the serial device to ensure exclusive access to the device.
Always forced on the Trimble NetRS.
- 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). (Note that for IPv6 MRU must be at least 1280)
- mtu n
- Set the MTU [Maximum Transmit Unit] value to n. Unless
the peer requests a smaller value via MRU negotiation, pppd will
request that the kernel networking code send data packets of no
more than n bytes through the PPP network interface. (Note
that for IPv6 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>
- Not available in the Trimble NetRS.
- active-filter filter-expression
- Specifies a packet filter to be applied to data packets to
determine which packets are to be regarded as link activity, and
therefore reset the idle timer, or cause the link to be brought up
in demand-dialling mode. This option is useful in conjunction with
the idle option if there are packets being sent or received
regularly over the link (for example, routing information packets)
which would otherwise prevent the link from ever appearing to be
idle. The filter-expression syntax is as described for tcpdump(1),
except that qualifiers which are inappropriate for a PPP link, such
as ether and arp, are not permitted. Generally the
filter expression should be enclosed in single-quotes to prevent
whitespace in the expression from being interpreted by the shell.
This option is currently only available under NetBSD, and then only
if both the kernel and pppd were compiled with PPP_FILTER defined.
- allow-ip address(es)
- Allow peers to use the given IP address or subnet without
authenticating themselves. The parameter is parsed as for each
element of the list of allowed IP addresses in the secrets files
(see the AUTHENTICATION section below).
- 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.
- cdtrcts
- Use a non-standard hardware flow control (i.e. DTR/CTS) to
control the flow of data on the serial port. If neither the
crtscts, the nocrtscts, the cdtrcts nor the
nocdtrcts option is given, the hardware flow control setting
for the serial port is left unchanged. Some serial ports (such as
Macintosh serial ports) lack a true RTS output. Such serial ports
use this mode to implement true bi-directional flow control. The
sacrifice is that this flow control mode does not permit using DTR
as a modem control line.
- chap-interval n
- If this option is given, pppd will rechallenge the peer every
n seconds.
- chap-max-challenge n
- Set the maximum number of CHAP challenge transmissions to
n (default 10).
- chap-restart n
- Set the CHAP restart interval (retransmission timeout for
challenges) to n seconds (default 3).
- connect-delay n
- Wait for up n milliseconds after the connect script
finishes for a valid PPP packet from the peer. At the end of this
time, or when a valid PPP packet is received from the peer, pppd
will commence negotiation by sending its first LCP packet. The
default value is 1000 (1 second). This wait period only applies if
the connect or pty option is used.
- debug
- Enables connection debugging facilities. If this option is
given, pppd will log the contents of all control packets sent or
received in a readable form. The packets are logged through syslog
with facility daemon and level debug. This
information can be directed to a file by setting up
/etc/syslog.conf appropriately (see syslog.conf(5)).
- default-asyncmap
- Disable asyncmap negotiation, forcing all control characters to
be escaped for both the transmit and the receive direction.
- default-mru
- Disable MRU [Maximum Receive Unit] negotiation. With this
option, pppd will use the default MRU value of 1500 bytes for both
the transmit and receive direction.
- deflate nr,nt
- Request that the peer compress packets that it sends, using the
Deflate scheme, with a maximum window size of 2**nr bytes,
and agree to compress packets sent to the peer with a maximum
window size of 2**nt bytes. If nt is not specified,
it defaults to the value given for nr. Values in the range 9
to 15 may be used for nr and nt; larger values give
better 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.
- 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.
- 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.
- hide-password
- When logging the contents of PAP packets, this option causes
pppd to exclude the password string from the log. This is the
default.
- holdoff n
- Specifies how many seconds to wait before re-initiating the
link after it terminates. This option only has any effect if the
persist or demand option is used. The holdoff period
is not applied if the link was terminated because it was idle.
- idle n
- Specifies that pppd should disconnect if the link is idle for
n seconds. The link is idle when no data packets (i.e. IP
packets) are being sent or received. Note: it is not advisable to
use this option with the persist option without the
demand option. If the active-filter option is given,
data packets which are rejected by the specified activity filter
also count as the link being idle.
- ipcp-accept-local
- With this option, pppd will accept the peer's idea of our local
IP address, even if the local IP address was specified in an
option.
- ipcp-accept-remote
- With this option, pppd will accept the peer's idea of its
(remote) IP address, even if the remote IP address was specified in
an option.
- ipcp-max-configure n
- Set the maximum number of IPCP configure-request transmissions
to n (default 10).
- ipcp-max-failure n
- Set the maximum number of IPCP configure-NAKs returned before
starting to send configure-Rejects instead to n (default
10).
- ipcp-max-terminate n
- Set the maximum number of IPCP terminate-request transmissions
to n (default 3).
- ipcp-restart n
- Set the IPCP restart interval (retransmission timeout) to
n seconds (default 3).
- ipparam string
- Provides an extra parameter to the ip-up and ip-down scripts.
If this option is given, the string supplied is given as the
6th parameter to those scripts.
- ipv6cp-max-configure n
- Not available in the Trimble NetRS.
- ipv6cp-max-failure n
- Not available in the Trimble NetRS.
- ipv6cp-max-terminate n
- Not available in the Trimble NetRS.
- ipv6cp-restart n
- Not available in the Trimble NetRS.
- ipx
- Not available in the Trimble NetRS.
- ipx-network n
- Not available in the Trimble NetRS.
- ipx-node n:m
- Not available in the Trimble NetRS.
- ipx-router-name <string>
- Not available in the Trimble NetRS.
- ipx-routing n
- Not available in the Trimble NetRS.
- ipxcp-accept-local
- Not available in the Trimble NetRS.
- ipxcp-accept-network
- Not available in the Trimble NetRS.
- ipxcp-accept-remote
- Not available in the Trimble NetRS.
- ipxcp-max-configure n
- Not available in the Trimble NetRS.
- ipxcp-max-failure n
- Not available in the Trimble NetRS.
- ipxcp-max-terminate n
- Not available in the Trimble NetRS.
- kdebug n
- Enable debugging code in the kernel-level PPP driver. The
argument values depend on the specific kernel driver, but in
general a value of 1 will enable general kernel debug messages.
(Note that these messages are usually only useful for debugging the
kernel driver itself.) For the Linux 2.2.x kernel driver, the value
is a sum of bits: 1 to enable general debug messages, 2 to request
that the contents of received packets be printed, and 4 to request
that the contents of transmitted packets be printed. On most
systems, messages printed by the kernel are logged by syslog(1) to a
file as directed in the /etc/syslog.conf configuration file.
- ktune
- Not available in the Trimble NetRS.
- lcp-echo-failure n
- If this option is given, pppd will presume the peer to be dead
if n LCP echo-requests are sent without receiving a valid
LCP echo-reply. If this happens, pppd will terminate the
connection. Use of this option requires a non-zero value for the
lcp-echo-interval parameter. This option can be used to
enable pppd to terminate after the physical connection has been
broken (e.g., the modem has hung up) in situations where no
hardware modem control lines are available.
- lcp-echo-interval n
- If this option is given, pppd will send an LCP echo-request
frame to the peer every n seconds. Normally the peer should
respond to the echo-request by sending an echo-reply. This option
can be used with the lcp-echo-failure option to detect that
the peer is no longer connected.
- lcp-max-configure n
- Set the maximum number of LCP configure-request transmissions
to n (default 10).
- lcp-max-failure n
- Set the maximum number of LCP configure-NAKs returned before
starting to send configure-Rejects instead to n (default
10).
- lcp-max-terminate n
- Set the maximum number of LCP terminate-request transmissions
to n (default 3).
- lcp-restart n
- Set the LCP restart interval (retransmission timeout) to
n seconds (default 3).
- linkname name
- Sets the logical name of the link to name. Pppd will
create a file named ppp-name.pid in /var/run
(or /etc/ppp on some systems) containing its 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.
- 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
- Not available in the Trimble NetRS.
- login
- Use the system password database for authenticating the peer
using PAP, and record the user in the system wtmp file. Note that
the peer must have an entry in the /etc/ppp/pap-secrets file as
well as the system password database to be allowed access.
- maxconnect n
- Terminate the connection when it has been available for network
traffic for n seconds (i.e. n seconds after the first
network control protocol comes up).
- maxfail n
- Terminate after n consecutive failed connection
attempts. A value of 0 means no limit. The default value is 10.
- modem
- Use the modem control lines. This option is the default. With
this option, pppd will wait for the CD (Carrier Detect) signal from
the modem to be asserted when opening the serial device (unless a
connect script is specified), and it will drop the DTR (Data
Terminal Ready) signal briefly when the connection is terminated
and before executing the connect script.
This option is forced in the Trimble NetRS.
- mp
- Not available in the Trimble NetRS.
- mpshortseq
- Not available in the Trimble NetRS.
- mrru n
- Sets the Maximum Reconstructed Receive Unit to n. The
MRRU is the maximum size for a received packet on a multilink
bundle, and is analogous to the MRU for the individual links. This
option is currently only available under Linux, and only has any
effect if multilink is enabled (see the multilink option).
- ms-dns <addr>
- Not available in the Trimble NetRS.
- ms-wins <addr>
- Not available in the Trimble NetRS.
- multilink
- Not available in the Trimble NetRS.
- 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. (Note: on some platforms, pppd will always use
255.255.255.255 for the netmask, if that is the only appropriate
value for a point-to-point interface.)
- noaccomp
- Disable Address/Control compression in both directions (send
and receive).
- noauth
- Do not require the peer to authenticate itself. This option is
always forced in the Trimble NetRS.
- 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.
- 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.
This option is always forced on the Trimble NetRS.
- noendpoint
- Disables pppd from sending an endpoint discriminator to the
peer or accepting one from the peer (see the MULTILINK section
below). This option should only be required if the peer is buggy.
- noip
- Disable IPCP negotiation and IP communication. This option
should only be required if the peer is buggy and gets confused by
requests from pppd for IPCP negotiation.
- noipv6
- Disable IPv6CP negotiation and IPv6 communication. This option
should only be required if the peer is buggy and gets confused by
requests from pppd for IPv6CP negotiation.
- noipdefault
- Disables the default behaviour when no local IP address is
specified, which is to determine (if possible) the local IP address
from the hostname. With this option, the peer will have to supply
the local IP address during IPCP negotiation (unless it specified
explicitly on the command line or in an options file).
- noipx
- Disable the IPXCP and IPX protocols. This option should only be
required if the peer is buggy and gets confused by requests from
pppd for IPXCP negotiation.
- noktune
- Opposite of the ktune option; disables pppd from
changing system settings.
- nolog
- Do not send log messages to a file or file descriptor. This
option cancels the logfd and logfile options.
- nomagic
- Disable magic number negotiation. With this option, pppd cannot
detect a looped-back line. This option should only be needed if the
peer is buggy.
- nomp
- Disables the use of PPP multilink. This option is currently
only available under Linux.
- 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.
- noproxyarp
- Disable the proxyarp option. The system administrator
who wishes to prevent users from creating proxy ARP entries with
pppd can do so by placing this option in the /etc/ppp/options file.
- notty
- Normally, pppd requires a terminal device. With this option,
pppd will allocate itself a pseudo-tty master/slave pair and use
the slave as its 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 standard input even if they are not terminal devices. This
option increases the latency and CPU overhead of transferring data
over the ppp interface as all of the characters sent and received
must flow through the character shunt process. An explicit device
name may not be given if this option is used.
- novj
- Disable Van Jacobson style TCP/IP header compression in both
the transmit and the receive direction.
- novjccomp
- Disable the connection-ID compression option in Van Jacobson
style TCP/IP header compression. With this option, pppd will not
omit the connection-ID byte from Van Jacobson compressed TCP/IP
headers, nor ask the peer to do so.
- papcrypt
- Indicates that all secrets in the /etc/ppp/pap-secrets file
which are used for checking the identity of the peer are encrypted,
and thus pppd should not accept a password which, before
encryption, is identical to the secret from the
/etc/ppp/pap-secrets file.
- pap-max-authreq n
- Set the maximum number of PAP authenticate-request
transmissions to n (default 10).
- pap-restart n
- Set the PAP restart interval (retransmission timeout) to
n seconds (default 3).
- pap-timeout n
- Set the maximum time that pppd will wait for the peer to
authenticate itself with PAP to n seconds (0 means no
limit).
- pass-filter filter-expression
- Specifies a packet filter to applied to data packets being sent
or received to determine which packets should be allowed to pass.
Packets which are rejected by the filter are silently discarded.
This option can be used to prevent specific network daemons (such
as routed) using up link bandwidth, or to provide a 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 permitted. Generally the
filter expression should be enclosed in single-quotes to prevent
whitespace in the expression from being interpreted by the shell.
Note that it is possible to apply different constraints to incoming
and outgoing packets using the inbound and outbound
qualifiers. This option is currently only available under NetBSD,
and then only if both the kernel and pppd were compiled with
PPP_FILTER defined.
- persist
- Do not exit after a connection is terminated; instead try to
reopen the connection.
- plugin filename
- Load the shared library object file filename as a
plugin. This is a privileged option.
- 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.
- privgroup group-name
- Allows members of group group-name to use privileged
options. This is a privileged option. Use of this option requires
care as there is no guarantee that members of group-name
cannot use pppd to become root themselves. Consider it equivalent
to putting the members of group-name in the kmem or disk
group.
- proxyarp
- Add an entry to this system's ARP [Address Resolution Protocol]
table with the IP address of the peer and the Ethernet address of
this system. This will have the effect of making the peer appear to
other systems to be on the local ethernet.
- pty script
- Specifies that the command script is to be used to
communicate rather than a specific terminal device. Pppd will
allocate itself a pseudo-tty master/slave pair and use the slave as
its terminal device. The script will be run in a child
process with the pseudo-tty master as its standard input and
output. An explicit device name may not be given if this option is
used. (Note: if the record option is used in conjuction with
the pty option, the child process will have pipes on its
standard input and output.)
- receive-all
- With this option, pppd will accept all control characters from
the peer, including those marked in the receive asyncmap. Without
this option, pppd will discard those characters as specified in
RFC1662. This option should only be needed if the peer is buggy.
- record filename
- Specifies that pppd should record all characters sent and
received to a file named filename. This file is opened in
append mode, using the user's user-ID and permissions. This option
is implemented using a pseudo-tty and a process to transfer
characters between the pseudo-tty and the real serial device, so it
will increase the latency and CPU overhead of transferring data
over the ppp interface. The characters are stored in a tagged
format with timestamps, which can be displayed in readable form
using the pppdump(8)
program.
- remotename name
- Set the assumed name of the remote system for 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.
- 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).
- 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.
- updetach
- With this option, pppd will detach from its controlling
terminal once it has successfully established the ppp connection
(to the point where the first network control protocol, usually the
IP control protocol, has come up).
- usehostname
- Enforce the use of the hostname (with domain name appended, if
given) as the name of the local system for authentication purposes
(overrides the name option). This option is not normally
needed since the name option is privileged.
- usepeerdns
- Ask the peer for up to 2 DNS server addresses. The addresses
supplied by the peer (if any) are passed to the /etc/ppp/ip-up
script in the environment variables DNS1 and DNS2. In addition,
pppd will create an /etc/ppp/resolv.conf file containing one or two
nameserver lines with the address(es) supplied by the peer.
- user name
- Sets the name used for authenticating the local system to the
peer to name.
- vj-max-slots n
- Sets the number of connection slots to be used by the Van
Jacobson TCP/IP header compression and decompression code to
n, which must be between 2 and 16 (inclusive).
- welcome script
- Run the executable or shell command specified by script
before initiating PPP negotiation, after the connect script (if
any) has completed. A value for this option from a privileged
source cannot be overridden by a non-privileged user.
- xonxoff
- Use software flow control (i.e. XON/XOFF) to 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
authenticated identity (if any), and through restrictions on which
options a non-privileged user may use. Several of pppd's options
are privileged, in particular those which permit potentially
insecure configurations; these options are only accepted in files
which are under the control of the system administrator, or if pppd
is being run by root.
The default behaviour of pppd is to allow an unauthenticated
peer to use a given IP address only if the system does not already
have a route to that IP address. For example, a system with a
permanent connection to the wider internet will normally have a
default route, and thus all peers will have to authenticate
themselves in order to set up a connection. On such a system, the
auth option is the default. On the other hand, a system
where the PPP link is the only connection to the 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 names
used for authentication correspond to the internet hostnames of the
peers, but this is not essential.
At present, pppd supports two authentication protocols: the
Password Authentication Protocol (PAP) and the Challenge Handshake
Authentication Protocol (CHAP). PAP involves the client sending its
name and a cleartext password to the server to authenticate itself.
In contrast, the server initiates the CHAP authentication exchange
by sending a challenge to the client (the challenge packet includes
the server's name). The client must respond with a response which
includes its name plus a hash value derived from the shared secret
and the challenge, in order to prove that it knows the secret.
The PPP protocol, being symmetrical, allows both peers to
require the other to authenticate itself. In that case, two
separate and independent authentication exchanges will occur. The
two exchanges could use different authentication protocols, and in
principle, different names could be used in the two exchanges.
The default behaviour of pppd is to agree to authenticate if
requested, and to not require authentication from the peer.
However, pppd will not agree to authenticate itself with a
particular protocol if it has no secrets which could be used to do
so.
Pppd stores secrets for use in authentication in secrets files
(/etc/ppp/pap-secrets for PAP, /etc/ppp/chap-secrets for CHAP).
Both 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.
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 authentication is being
used, because the peer will have sent it in the challenge packet.
However, if PAP is being used, pppd will have to determine the
peer's name from the options specified by the user. The user can
specify the peer's name directly with the remotename option.
Otherwise, if the remote IP address was specified by a name (rather
than in numeric form), that name will be used as the peer's name.
Failing that, pppd will use the null string as the peer's name.
When authenticating the peer with PAP, the supplied password is
first compared with the secret from the secrets file. If the
password doesn't match the secret, the password is encrypted using
crypt() and checked against the secret again. Thus secrets for
authenticating the peer can be stored in encrypted form if desired.
If the papcrypt option is given, the first (unencrypted)
comparison is omitted, for better security.
Furthermore, if the login option was specified, the
username and password are also checked against the system password
database. Thus, the system administrator can set up the pap-secrets
file to allow PPP access only to certain users, and to restrict the
set of IP addresses that each user can use. Typically, when using
the login option, the secret in /etc/ppp/pap-secrets would
be "", which will match any password supplied by the peer. This
avoids the need to have the same secret in two places.
Authentication must be satisfactorily completed before IPCP (or
any other Network Control Protocol) can be started. If the peer is
required to authenticate itself, and fails to do so, pppd will
terminated the link (by closing LCP). If IPCP negotiates an
unacceptable IP address for the remote host, IPCP will be closed.
IP packets can only be sent or received when IPCP is open.
In some cases it is desirable to allow some hosts which can't
authenticate themselves to connect and use one of a restricted set
of IP addresses, even when the local host generally requires
authentication. If the peer refuses to authenticate itself when
requested, pppd takes that as equivalent to authenticating with PAP
using the empty string for the username and password. Thus, by
adding a line to the pap-secrets file which specifies the empty
string for the client and password, it is possible to allow
restricted access to hosts which refuse to authenticate themselves.
ROUTING
When IPCP negotiation is completed successfully, pppd will
inform the kernel of the local and remote IP addresses for the ppp
interface. This is sufficient to create a host route to the remote
end of the link, which will enable the peers to exchange IP
packets. Communication with other machines generally requires
further modification to routing tables and/or ARP (Address
Resolution Protocol) tables. In most cases the defaultroute
and/or proxyarp options are sufficient for this, but in some
cases further intervention is required. The /etc/ppp/ip-up script
can be used for this.
Sometimes it is desirable to add a default route through the
remote host, as in the case of a machine whose only connection to
the Internet is through the ppp interface. The defaultroute
option causes pppd to create such a default route when IPCP comes
up, and delete it when the link is terminated.
In some cases it is desirable to use proxy ARP, for example on a
server machine connected to a LAN, in order to allow other hosts to
communicate with the remote host. The proxyarp option causes
pppd to look for a network interface on the same subnet as the
remote host (an interface supporting broadcast and ARP, which is up
and not a point-to-point or loopback interface). If found, pppd
creates a permanent, published ARP entry with the IP address of the
remote host and the hardware address of the 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
This section is not applicable on the Trimble NetRS.
EXAMPLES
The following examples assume that the /etc/ppp/options file
contains the auth option (as in the default /etc/ppp/options
file in the ppp distribution).
Probably the most common use of pppd is to dial out to an ISP.
This can be done with a command such as
- pppd call isp
where the /etc/ppp/peers/isp file is set up by the system
administrator to contain something like this:
- ttyS0 19200 crtscts
connect '/usr/sbin/chat -v -f /etc/ppp/chat-isp'
noauth
In this example, we are using chat to dial the ISP's modem and
go through any logon sequence required. The /etc/ppp/chat-isp file
contains the script used by chat; it could for example contain
something like this:
- ABORT "NO CARRIER"
ABORT "NO DIALTONE"
ABORT "ERROR"
ABORT "NO ANSWER"
ABORT "BUSY"
ABORT "Username/Password Incorrect"
"" "at"
OK "at&d0&c1"
OK "atdt2468135"
"name:" "^Umyuserid"
"word:" "\qmypassword"
"ispts" "\q^Uppp"
"~-^Uppp-~"
See the chat(8) man page
for details of chat scripts.
Pppd can also be used to provide a dial-in ppp service for
users. If the users already have login accounts, the simplest way
to set up the ppp service is to let the users log in to their
accounts and run pppd (installed setuid-root) with a command such
as
- pppd proxyarp
To allow a user to use the PPP facilities, you need to allocate
an IP address for that user's machine and create an entry in
/etc/ppp/pap-secrets or /etc/ppp/chap-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" which 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
Alternatively, you can create a username called (for example)
"ppp", whose login shell is pppd and whose home directory is
/etc/ppp. Options to be used when pppd is run this way can be put
in /etc/ppp/.ppprc.
If your serial connection is any more complicated than a piece
of wire, you may need to arrange for some control characters to be
escaped. In particular, it is often useful to escape XON (^Q) and
XOFF (^S), using asyncmap a0000. If the path includes a
telnet, you probably should escape ^] as well (asyncmap
200a0000). If the path includes an rlogin, you will need to use
the escape ff option on the end which is running the rlogin
client, since many rlogin implementations are not transparent; they
will remove the sequence [0xff, 0xff, 0x73, 0x73, followed by any 8
bytes] from the stream.
DIAGNOSTICS
Messages are sent to the syslog daemon using facility
LOG_DAEMON. (This can be 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.
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.
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).
- 19
- We failed to authenticate ourselves to the peer.
SCRIPTS
This section is not applicable on the Trimble NetRS.
FILES
This section is not applicable on the Trimble NetRS.
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.
- RFC2472
- Haskin, D. IP Version 6 over PPP December 1998.
NOTES
This section is not applicable on the Trimble NetRS.
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.