pppd
Point-to-Point Protocol Daemon
see also :
chat - pppstats
Synopsis
pppd [
options ]
add an example, a script, a trick and tips
examples
The following examples assume that the /etc/ppp/options file
contains the auth option (as in the default
/etc/ppp/options file in the ppp distribution).
Probably the most common use of pppd is to dial out to an ISP.
This can be done with a command such as
pppd call isp
where the /etc/ppp/peers/isp file is set up by the system
administrator to contain something like this:
ttyS0 19200 crtscts
connect ’/usr/sbin/chat -v -f /etc/ppp/chat-isp’
noauth
In this example, we are using chat to dial the ISP’s modem and go
through any logon sequence required. The /etc/ppp/chat-isp file
contains the script used by chat; it could for example contain
something like this:
ABORT "NO CARRIER"
ABORT "NO DIALTONE"
ABORT "ERROR"
ABORT "NO ANSWER"
ABORT "BUSY"
ABORT "Username/Password Incorrect"
"" "at"
OK "at&d0&c1"
OK "atdt2468135"
"name:" "^Umyuserid"
"word:" "\qmypassword"
"ispts" "\q^Uppp"
"~-^Uppp-~"
See the chat(8) man page for details of chat scripts.
Pppd can also be used to provide a dial-in ppp service for users.
If the users already have login accounts, the simplest way to set
up the ppp service is to let the users log in to their accounts
and run pppd (installed setuid-root) with a command such as
pppd proxyarp
To allow a user to use the PPP facilities, you need to allocate
an IP address for that user’s machine and create an entry in
/etc/ppp/pap-secrets, /etc/ppp/chap-secrets, or
/etc/ppp/srp-secrets (depending on which 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 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.
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.
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
Enable the IPv6CP and IPv6 protocols.
ipv6
<local_interface_identifier>,<remote_interface_identifier>
Set the local and/or remote
64-bit interface identifier. Either one may be omitted. The
identifier must be specified in standard ascii notation of
IPv6 addresses (e.g. ::dead:beef). If the
ipv6cp-use-ipaddr option is given, the
local identifier is the local IPv4 address (see above). On
systems which supports a unique persistent id, such as
EUI-48 derived from the Ethernet MAC address,
ipv6cp-use-persistent option can be used
to replace the ipv6 <local>,<remote>
option. Otherwise the identifier is randomized.
active-filter
filter-expression
Specifies a packet filter to be
applied to data packets to determine which packets are to be
regarded as link activity, and therefore reset the idle
timer, or cause the link to be brought up in demand-dialling
mode. This option is useful in conjunction with the
idle option if there are packets being sent or
received regularly over the link (for example, routing
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 Linux, and requires that
the kernel was configured to include PPP filtering support
(CONFIG_PPP_FILTER). Note that it is possible to apply
different constraints to incoming and outgoing packets using
the inbound and outbound qualifiers.
allow-ip
address(es)
Allow peers to use the given IP
address or subnet without authenticating themselves. The
parameter is parsed as for each element of the list of
allowed IP addresses in the secrets files (see the
AUTHENTICATION section below).
allow-number
number
Allow peers to connect from the
given telephone number. A trailing ’*’ character
will match all numbers beginning with the leading part.
bsdcomp nr,nt
Request that the peer compress
packets that it sends, using the BSD-Compress scheme, with a
maximum code size of nr bits, and agree to compress
packets sent to the peer with a maximum code size of
nt bits. If nt is not 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).
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 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 conjunction 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.
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 number of EAP
Requests to which pppd will respond (as a client) without
hearing EAP Success or Failure. (Default is 20.)
eap-max-sreq
n
Set the maximum number of EAP
Requests that pppd will issue (as a server) while attempting
authentication. (Default is 10.)
eap-restart
n
Set the retransmit timeout for
EAP Requests when acting as a server (authenticator).
(Default is 3 seconds.)
eap-timeout
n
Set the maximum time to wait
for the peer to send an EAP Request when acting as a client
(authenticatee). (Default is 20 seconds.)
hide-password
When logging the contents of
PAP packets, this option causes pppd to exclude the password
string from the log. This is the default.
holdoff n
Specifies how many seconds to
wait before re-initiating the link after it terminates. This
option only has any effect if the persist or
demand option is used. The holdoff period is not
applied if the link was terminated because it was idle.
idle n
Specifies that pppd should disconnect if the link is
idle for n seconds. The link is idle when no data
packets (i.e. IP packets) are being sent or received. Note:
it is not advisable to use this option with the
persist option without the demand option. If
the active-filter option is given, data packets
which are rejected by the specified activity filter also
count as the link being idle.
ipcp-accept-local
With this option, pppd will
accept the peer’s idea of our local IP address, even
if the local IP address was 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-accept-local
With this option, pppd will
accept the peer’s idea of our local IPv6 interface
identifier, even if the local IPv6 interface identifier was
specified in an option.
ipv6cp-max-configure
n
Set the maximum number of
IPv6CP configure-request transmissions to n (default
10).
ipv6cp-max-failure
n
Set the maximum number of
IPv6CP configure-NAKs returned before starting to send
configure-Rejects instead to n (default 10).
ipv6cp-max-terminate
n
Set the maximum number of
IPv6CP terminate-request transmissions to n (default
3).
ipv6cp-restart
n
Set the IPv6CP restart interval
(retransmission timeout) to n seconds (default
3).
ipx
Enable the IPXCP and IPX protocols. This option is
presently only supported under Linux, and only if your
kernel has been configured to include IPX support.
ipx-network
n
Set the IPX network number in
the IPXCP configure request frame to n, a hexadecimal
number (without a leading 0x). There is no valid default. If
this option is not specified, the network number is obtained
from the peer. If the peer does not have the network number,
the IPX protocol will not be started.
ipx-node
n:m
Set the IPX node numbers. The
two node numbers are separated from each other with a colon
character. The first number n is the local node
number. The second number m is the peer’s node
number. Each node number is a hexadecimal number, at most 10
digits long. The node numbers on the ipx-network must
be unique. There is no valid default. If this option is not
specified then the node numbers are obtained from the
peer.
ipx-router-name
<string>
Set the name of the router.
This is a string and is sent to the peer as information
data.
ipx-routing
n
Set the routing protocol to be
received by this option. More than one instance of
ipx-routing may be specified. The
’none’ option (0) may be specified as the
only instance of ipx-routing. The values may be
0 for NONE, 2 for RIP/SAP, and
4 for NLSP.
ipxcp-accept-local
Accept the peer’s NAK for
the node number specified in the ipx-node option. If a
node number was specified, and non-zero, the default is to
insist that the value be used. If you include this option
then you will permit the peer to override the entry of the
node number.
ipxcp-accept-network
Accept the peer’s NAK for
the network number specified in the ipx-network
option. If a network number was specified, and non-zero, the
default is to insist that the value be used. If you include
this option then you will permit the peer to override the
entry of the node number.
ipxcp-accept-remote
Use the peer’s network
number specified in the configure request frame. If a node
number was specified for the peer and this option was not
specified, the peer will be forced to use the value which
you have specified.
ipxcp-max-configure
n
Set the maximum number of IPXCP
configure request frames which the system will send to
n. The default is 10.
ipxcp-max-failure
n
Set the maximum number of IPXCP
NAK frames which the local system will send before it
rejects the options. The default value is 3.
ipxcp-max-terminate
n
Set the maximum nuber of IPXCP
terminate request frames before the local system considers
that the peer is not listening to them. The default value is
3.
kdebug n
Enable debugging code in the
kernel-level PPP driver. The argument values depend on the
specific kernel driver, but in general a value of 1 will
enable general kernel debug messages. (Note that these
messages are usually only useful for debugging the kernel
driver itself.) For the Linux 2.2.x kernel driver, the value
is a sum of bits: 1 to enable general debug messages, 2 to
request that the contents of received packets be printed,
and 4 to request that the contents of transmitted packets be
printed. On most systems, messages printed by the kernel are
logged by syslog(1) to a file as directed in the
/etc/syslog.conf configuration file.
ktune
Enables pppd to alter kernel settings as appropriate.
Under Linux, pppd will enable IP forwarding (i.e. set
/proc/sys/net/ipv4/ip_forward to 1) if the proxyarp
option is used, and will enable the dynamic IP address
option (i.e. set /proc/sys/net/ipv4/ip_dynaddr to 1) in
demand mode if the local address changes.
lcp-echo-adaptive
If this option is used with the
lcp-echo-failure option then pppd will
send LCP echo-request frames only if no traffic was
received from the peer since the last echo-request was
sent.
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. 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 system wtmp file.
Note that the peer must have an entry in the
/etc/ppp/pap-secrets file as well as the system
password database to be allowed access. See also the
enable-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 currently
only available under Linux.
mppe-stateful
Allow MPPE to use stateful
mode. Stateless mode is still attempted first. The default
is to disallow stateful mode.
mpshortseq
Enables the use of short
(12-bit) sequence numbers in multilink headers, as opposed
to 24-bit sequence numbers. This option is only available
under Linux, and only has any effect if multilink is enabled
(see the multilink option).
mrru n
Sets the Maximum Reconstructed Receive Unit to n.
The MRRU is the maximum size for a received packet on a
multilink bundle, and is analogous to the MRU for the
individual links. This option is currently only available
under Linux, and only has any effect if multilink is enabled
(see the multilink option).
ms-dns
<addr>
If pppd is acting as a server
for Microsoft Windows clients, this option allows pppd to
supply one or two DNS (Domain Name Server) addresses to the
clients. The first instance of this option specifies the
primary DNS address; the second instance (if given)
specifies the secondary DNS address. (This option was
present in some older versions of pppd under the name
dns-addr.)
ms-wins
<addr>
If pppd is acting as a server
for Microsoft Windows or "Samba" clients, this
option allows pppd to supply one or two WINS (Windows
Internet Name Services) server addresses to the clients. The
first instance of this option specifies the primary WINS
address; the second instance (if given) specifies the
secondary WINS address.
multilink
Enables the use of the PPP
multilink protocol. If the peer also supports multilink,
then this link can become part of a bundle between the local
system and the peer. If there is an existing bundle to the
peer, pppd will join this link to that bundle, otherwise
pppd will create a new bundle. See the MULTILINK section
below. This option is currently only available under
Linux.
name name
Set the name of the local
system for authentication 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 adding a default route with pppd can do so by placing
this option in the /etc/ppp/options file.
noreplacedefaultroute
Disable the
replacedefaultroute option. The system administrator
who wishes to prevent users from replacing a default route
with pppd can do so by placing this option in the
/etc/ppp/options file.
nodeflate
Disables Deflate compression;
pppd will not request or agree to compress packets using the
Deflate scheme.
nodetach
Don’t detach from the
controlling terminal. Without this option, if a serial
device other than the terminal on the standard input is
specified, pppd will fork to become a background
process.
noendpoint
Disables pppd from sending an
endpoint discriminator to the peer or accepting one from the
peer (see the 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.
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.
noproxyarp
Disable the proxyarp
option. The system administrator who wishes to prevent users
from creating proxy ARP entries with pppd can do so by
placing this option in the /etc/ppp/options file.
noremoteip
Allow pppd to operate without
having an IP address for the peer. This option is only
available under Linux. Normally, pppd will request the
peer’s IP address, and if the peer does not supply it,
pppd will not bring up the link for IP traffic. With this
option, if the peer does not supply its IP address, pppd
will not ask the peer for it, and will not set the
destination address of the ppp interface. In this situation,
the ppp interface can be used for routing by creating device
routes, but the peer itself cannot be addressed directly for
IP traffic.
notty
Normally, pppd requires a terminal device. With this
option, pppd will allocate itself a pseudo-tty 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 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 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 Linux, and requires that
the kernel was configured to include PPP filtering support
(CONFIG_PPP_FILTER).
password
password-string
Specifies the password to use
for authenticating to the peer. Use of this option is
discouraged, as the password is likely to be visible to
other users on the system (for example, by using ps(1)).
persist
Do not exit after a connection
is terminated; instead try to reopen the 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, where version is the
version number of pppd (for example, 2.4.2).
predictor1
Request that the peer compress
frames that it sends using Predictor-1 compression, and
agree to compress 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 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 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.
remotenumber
number
Set the assumed telephone
number of the remote system for authentication purposes to
number.
refuse-chap
With this option, pppd will not
agree to authenticate itself to the peer using CHAP.
refuse-mschap
With this option, pppd will not
agree to authenticate itself to the peer using
MS-CHAP.
refuse-mschap-v2
With this option, pppd will not
agree to authenticate itself to the peer using
MS-CHAPv2.
refuse-eap
With this option, pppd will not
agree to authenticate itself to the peer using EAP.
refuse-pap
With this option, pppd will not
agree to authenticate itself to the peer using PAP.
require-chap
Require the peer to
authenticate itself using CHAP [Challenge Handshake
Authentication Protocol] authentication.
require-mppe
Require the use of MPPE
(Microsoft Point to Point Encryption). This option disables
all other compression types. This option enables both 40-bit
and 128-bit encryption. In order for MPPE to successfully
come up, you must have authenticated with either
MS-CHAP or MS-CHAPv2. This option is presently
only supported under Linux, and only if your kernel has been
configured to include MPPE support.
require-mppe-40
Require the use of MPPE, with
40-bit encryption.
require-mppe-128
Require the use of MPPE, with
128-bit encryption.
require-mschap
Require the peer to
authenticate itself using MS-CHAP [Microsoft Challenge
Handshake Authentication Protocol] authentication.
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 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, and the environment
variable USEPEERDNS will be set to 1. In addition, pppd will
create an /etc/ppp/resolv.conf file containing one or two
nameserver lines with the address(es) supplied by the
peer.
user name
Sets the name used for
authenticating the local system to the peer to
name.
vj-max-slots
n
Sets the number of connection
slots to be used by the Van Jacobson TCP/IP header
compression and decompression code to n, which must
be between 2 and 16 (inclusive).
welcome
script
Run the executable or shell
command specified by script before initiating PPP
negotiation, after the connect script (if any) has
completed. A value for this option from a privileged source
cannot be overridden by a non-privileged user.
xonxoff
Use software flow control (i.e.
XON/XOFF) to control the flow of data on the serial
port.
authentication
Authentication is the process whereby one peer convinces the
other of its identity. This involves the first peer sending its
name to the other, together with some kind of secret information
which could only come from the genuine authorized user of that
name. In such an exchange, we will call the first peer the
"client" and the other the "server". The client has a name by
which it identifies itself to the server, and the server also has
a name by which it identifies itself to the client. Generally the
genuine client shares some secret (or password) with the server,
and authenticates itself by proving that it knows that secret.
Very often, the names used for authentication correspond to the
internet hostnames of the peers, but this is not essential.
At present, pppd supports three authentication protocols: the
Password Authentication Protocol (PAP), Challenge Handshake
Authentication Protocol (CHAP), and Extensible Authentication
Protocol (EAP). PAP involves the client sending its name and a
cleartext password to the server to authenticate itself. In
contrast, the server initiates the CHAP authentication exchange
by sending a challenge to the client (the challenge packet
includes the server’s name). The client must respond with a
response which includes its name plus a hash value derived from
the shared secret and the challenge, in order to prove that it
knows the secret. EAP supports CHAP-style authentication, and
also includes the SRP-SHA1 mechanism, which is resistant to
dictionary-based attacks and does not require a cleartext
password on the server side.
The PPP protocol, being symmetrical, allows both peers to require
the other to authenticate itself. In that case, two separate and
independent authentication exchanges will occur. The two
exchanges could use different authentication 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.
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.
copyright
Pppd is copyrighted and made available under conditions which
provide that it may be copied and used in source or binary forms
provided that the conditions listed below are met. Portions of
pppd are covered by the following copyright notices:
Copyright (c) 1984-2000 Carnegie Mellon University. All rights
reserved.
Copyright (c) 1993-2004 Paul Mackerras. All rights reserved.
Copyright (c) 1995 Pedro Roque Marques. All rights reserved.
Copyright (c) 1995 Eric Rosenquist. All rights reserved.
Copyright (c) 1999 Tommi Komulainen. All rights reserved.
Copyright (C) Andrew Tridgell 1999
Copyright (c) 2000 by Sun Microsystems, Inc. All rights
reserved.
Copyright (c) 2001 by Sun Microsystems, Inc. All rights
reserved.
Copyright (c) 2002 Google, Inc. All rights reserved.
The copyright notices contain the following statements.
Redistribution and use in source and binary forms, with or
without modification, are permitted provided that the following
conditions are met:
1. Redistributions of source code must retain the above
copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above
copyright
notice, this list of conditions and the following disclaimer
in
the documentation and/or other materials provided with the
distribution.
3. The name "Carnegie Mellon University" must not be used to
endorse or promote products derived from this software
without
prior written permission. For permission or any legal
details, please contact
Office of Technology Transfer
Carnegie Mellon University
5000 Forbes Avenue
Pittsburgh, PA 15213-3890
(412) 268-4387, fax: (412) 268-7395
tech-transfer[:at:]andrew.cmu[:dot:]edu
3b. The name(s) of the authors of this software must not be used
to
endorse or promote products derived from this software
without
prior written permission.
4. Redistributions of any form whatsoever must retain the
following
acknowledgments:
"This product includes software developed by Computing
Services
at Carnegie Mellon University
(http://www.cmu.edu/computing/)."
"This product includes software developed by Paul Mackerras
<paulus[:at:]samba[:dot:]org>".
"This product includes software developed by Pedro Roque
Marques
<pedro_m[:at:]yahoo[:dot:]com>".
"This product includes software developed by Tommi Komulainen
<Tommi.Komulainen[:at:]iki[:dot:]fi>".
CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD
TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON
UNIVERSITY BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL
DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE
USE OR PERFORMANCE OF THIS SOFTWARE.
THE AUTHORS OF THIS SOFTWARE DISCLAIM ALL WARRANTIES WITH REGARD
TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL THE AUTHORS BE
LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY
DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
PERFORMANCE OF THIS SOFTWARE.
device
The name of the serial tty device being used.
|
IPLOCAL
The IP address for the local end of the link. This is only set
when IPCP has come up.
IPREMOTE
The IP address for the remote end of the link. This is only set
when IPCP has come up.
PEERNAME
The authenticated name of the peer. This is only set if the peer
authenticates itself.
SPEED
The baud rate of the tty device.
ORIG_UID
The real user-id of the user who invoked pppd.
PPPLOGNAME
The username of the real user-id that invoked pppd. This is
always set.
For the ip-down and auth-down scripts, pppd also sets the
following variables giving statistics for the connection:
CONNECT_TIME
The number of seconds from when the PPP 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.
CALL_FILE
The value of the call option.
DNS1
If the peer supplies DNS server addresses, this variable is set
to the first DNS server address supplied.
DNS2
If the peer supplies DNS server addresses, this variable is set
to the second DNS server address supplied.
Pppd invokes the following scripts, if they exist. It is not an
error if they don’t exist.
/etc/ppp/auth-up
A program or script which is executed after the remote system
successfully authenticates itself. It is executed with the
parameters
interface-name peer-name user-name tty-device speed
Note that this script is not executed if the peer doesn’t
authenticate itself, for example when the noauth option is
used.
/etc/ppp/auth-down
A program or script which is executed when the link goes down, if
/etc/ppp/auth-up was previously executed. It is executed in the
same manner with the same parameters as /etc/ppp/auth-up.
/etc/ppp/ip-pre-up
A program or script which is executed just before the ppp network
interface is brought up. It is executed with the same parameters
as the ip-up script (below). At this point the interface exists
and has IP addresses assigned but is still down. This can be used
to add firewall rules before any IP traffic can pass through the
interface. Pppd will wait for this script to finish before
bringing the interface up, so this script should run quickly.
/etc/ppp/ip-up
A program or script which is executed when the link is available
for sending and receiving IP packets (that is, IPCP has come up).
It is 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.
diagnostics
Messages are sent to the syslog daemon using facility LOG_DAEMON.
(This can be overridden by recompiling pppd with the macro
LOG_PPP defined as the desired facility.) See the syslog(8)
documentation for details of where the syslog daemon will write
the messages. On most systems, the syslog daemon uses the
/etc/syslog.conf file to specify the destination(s) for syslog
messages. You may need to edit that file to suit.
The debug option causes the contents of all control
packets sent or received to be logged, that is, all LCP, PAP,
CHAP, EAP, or IPCP packets. This can be useful if the PPP
negotiation does not succeed or if authentication fails. If
debugging is enabled at compile time, the debug option
also causes other debugging messages to be logged.
Debugging can also be enabled or disabled by sending a SIGUSR1
signal to the pppd process. This signal acts as a toggle.
exit status
The exit status of pppd is set to indicate whether any error was
detected, or the reason for the link being terminated. The values
used are:
0
Pppd has detached, or otherwise the connection was successfully
established and terminated at the peer’s request.
1
An immediately fatal error of some kind occurred, such as an
essential 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.
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 running 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.
/etc/ppp/chap-secrets
Names, secrets and IP addresses for CHAP/MS-CHAP/MS-CHAPv2
authentication. As for /etc/ppp/pap-secrets, this file should be
owned by root and not readable or writable by any other user.
Pppd will log a warning if this is not the case.
/etc/ppp/srp-secrets
Names, secrets, and IP addresses for EAP authentication. As for
/etc/ppp/pap-secrets, this file should be owned by root and not
readable or writable by any other user. Pppd will log a warning
if this is not the case.
~/.ppp_pseudonym
Saved client-side SRP-SHA1 pseudonym. See the
srp-use-pseudonym option for details.
/etc/ppp/options
System default options for pppd, read before user default options
or 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.
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
appropriate phone number. This option specifies an command for
pppd to execute (by passing it to a shell) before attempting to
start PPP negotiation. The chat (8) program is often useful here,
as it provides a way to send arbitrary strings to a modem and
respond to received characters. A value for this option from a
privileged source cannot be overridden by a non-privileged user.
crtscts
Specifies that pppd should set the serial port to use hardware
flow control using the RTS and CTS signals in the RS-232
interface. If neither the crtscts, the nocrtscts,
the cdtrcts nor the nocdtrcts option is given, the
hardware flow control setting for the serial port is left
unchanged. Some serial ports (such as Macintosh serial ports)
lack a true RTS output. Such serial ports use this mode to
implement unidirectional flow control. The serial port will
suspend transmission when requested by the modem (via CTS) but
will be unable to request the modem to stop sending to the
computer. This mode retains the ability to use DTR as a modem
control line.
defaultroute
Add a default route to the system routing tables, using the peer
as the gateway, when IPCP negotiation is successfully completed.
This entry is removed when the PPP connection is broken. This
option is privileged if the nodefaultroute option has been
specified.
replacedefaultroute
This option is a flag to the defaultroute option. If defaultroute
is set and this flag is also set, pppd replaces an existing
default route with the new default route.
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 specified for the
escape option, unlike the asyncmap option which
only allows control characters to be specified. The characters
which may not be escaped are those with hex values 0x20 - 0x3f or
0x5e.
file name
Read options from file name (the format is described
below). The file must be readable by the user who has invoked
pppd.
init script
Execute the command specified by script, by passing it to
a shell, to initialize the serial line. This script would
typically use the chat(8) program to configure the modem to
enable auto answer. A value for this option from a privileged
source cannot be overridden by a non-privileged user.
lock
Specifies that pppd should create a UUCP-style lock file for the
serial device to ensure exclusive access to the device. By
default, pppd will not create a lock file.
mru n
Set the MRU [Maximum Receive Unit] value to n. Pppd will
ask the peer to send packets of no more than n bytes. The
value of n must be between 128 and 16384; the default is
1500. A value of 296 works well on very slow links (40 bytes for
TCP/IP header + 256 bytes of data). Note that for the IPv6
protocol, the MRU must be at least 1280.
mtu n
Set the MTU [Maximum Transmit Unit] value to n. Unless the
peer requests a smaller value via MRU negotiation, pppd will
request that the kernel networking code send data packets of no
more than n bytes through the PPP 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.
multilink
Multilink PPP provides the capability to combine two or more PPP
links between a pair of machines into a single ’bundle’, which
appears as a single virtual PPP link which has the combined
bandwidth of the individual links. Currently, multilink PPP is
only supported under Linux.
Pppd detects that the link it is controlling is connected to the
same peer as another link using the peer’s endpoint discriminator
and the authenticated identity of the peer (if it authenticates
itself). The endpoint discriminator is a block of data which is
hopefully unique for each peer. Several types of data can be
used, including locally-assigned strings of bytes, IP addresses,
MAC addresses, randomly strings of bytes, or E-164 phone numbers.
The endpoint discriminator sent to the peer by pppd can be set
using the endpoint option.
In 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 establishment of multiple bundles between the local system
and the peer. Pppd uses a TDB database in /var/run/pppd2.tdb to
match up links.
Assuming that multilink is enabled and the peer is willing to
negotiate multilink, then when pppd is invoked to bring up the
first link to the peer, it will detect that no other link is
connected to the peer and create a new bundle, that is, another
ppp network interface unit. When another pppd is invoked to bring
up another link to the peer, it will detect the existing bundle
and join its link to it.
If the first link terminates (for example, because of a hangup or
a received LCP terminate-request) the bundle is not destroyed
unless there are no other links remaining in the bundle. Rather
than exiting, the first pppd keeps running after its link
terminates, until all the links in the bundle have terminated. If
the first pppd receives a SIGTERM or SIGINT signal, it will
destroy the bundle and send a SIGHUP to the pppd processes for
each of the links in the bundle. If the first pppd receives a
SIGHUP signal, it will terminate its link but not the bundle.
Note: demand mode is not currently supported with multilink.
notes
Some limited degree of control can be exercised over a running
pppd process by sending it a signal from the list below.
SIGINT, SIGTERM
These signals cause pppd to terminate the link (by closing LCP),
restore the serial device settings, and exit. If a connector or
disconnector process is currently running, pppd will send the
same signal to its process group, so as to terminate the
connector or disconnector process.
SIGHUP
This signal causes pppd to terminate the link, restore the serial
device settings, and close the serial device. If the
persist or demand option has been specified, pppd
will try to reopen the serial device and start another connection
(after the holdoff period). Otherwise pppd will exit. If this
signal is received during the holdoff period, it causes pppd to
end the holdoff period immediately. If a connector or
disconnector process is running, pppd will send the same signal
to its process group.
SIGUSR1
This signal toggles the state of the debug option.
SIGUSR2
This signal causes pppd to renegotiate 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.)
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.
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.
scripts
Pppd invokes scripts at various stages in its processing which
can be used to perform site-specific ancillary processing. These
scripts are usually shell scripts, but could be executable code
files instead. Pppd does not wait for the scripts to finish
(except for the ip-pre-up script). The scripts are executed as
root (with the real and effective user-id set to 0), so that they
can do things such as update routing tables or run privileged
daemons. Be careful that the contents of these scripts do not
compromise your system’s security. Pppd runs the scripts with
standard input, output and error redirected to /dev/null, and
with an environment that is empty except for some environment
variables that give information about the link. The environment
variables that pppd sets are:
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.
see also
chat ,
pppstats
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.
RFC2284
Blunk, L.; Vollbrecht, J.,
PPP Extensible Authentication Protocol (EAP). March
1998.
RFC2472
Haskin, D. IP Version 6 over
PPP December 1998.
RFC2945
Wu, T., The SRP
Authentication and Key Exchange System September
2000.
draft-ietf-pppext-eap-srp-03.txt
Carlson, J.; et al., EAP
SRP-SHA1 Authentication Protocol. July 2001.
authors
Paul Mackerras
(paulus[:at:]samba[:dot:]org), based on earlier work by Drew Perkins,
Brad Clements, Karl Fox, Greg Christy, and Brad Parker.