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XRPi Documentation -
PPP -- Point to Point Protocol
DESCRIPTION
Point to Point Protocol (PPP) is a protocol suite intended for
use over simple links which transport packets between two
peers, such as an RS232 link (or pair of virtual COM ports).
Unlike SLIP, it includes facilities for link control (e.g.
management of a dial up link), user authentication,
negotiation of IP addresses, and the multiplexing of several
protocols across a common link.
PPP is designed to be self configuring. Most of the options
have standard default values, and peers negotiate anything
which differs from the default.
XRPi currently implements the most common PPP sub-protocols:
- Link Control Protocol (LCP)
- Password Authentication Protocol (PAP)
- IP Control Protocol (IPCP)
Most sysops will have no need to remember these protocol names
and acronyms. However, for those who wish to experiment, each
protocol has its own set of commands.
PPP has largely replaced SLIP for dial-up Internet access, and
the interconnection of peers via RS232.
If you want to know more about the internal workings of PPP,
it is specified in RFC1661.
Configuring XRPi for PPP
~~~~~~~~~~~~~~~~~~~~~~~~~~~
There are three ways in which PPP may be used:
- RS232 (and virtual COM port) links.
- Dial-in.
- Dial-out.
The first case requires an INTERFACE to be configured to use
PPP, but the other two cases temporarily establish a PPP link
on a MODEM interface. Each case is described in more detail
below:
Using PPP on Wire / Virtual COM Links
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In XROUTER.CFG, define an interface with TYPE=ASYNC and
PROTOCOL=PPP. For example:
INTERFACE=1
TYPE=ASYNC
COM=/dev/ttyUSB1 ; 1-4 or specify INTNUM/IOADDR
SPEED=19200 ; Adjust as necessary
PROTOCOL=PPP
MTU=1600
ENDINTERFACE
Then "bind" a port to that interface thus:
PORT=1
ID=PPP link to Win98 ; Text to identify port
INTERFACENUM=1 ; Bind to PPP interface
IPADDRESS=192.168.0.4 ; Optional (see below)
ENDPORT
The use of IPADDRESS is optional. If the keyword is omitted,
XRPi's "global" IP address will be used on that port. If the
address is specified as 0.0.0.0, it signifies that a "dynamic"
IP address should be obtained from the peer, otherwise the
specified address will be used.
The port is now ready for PPP using the standard PPP defaults,
but if it requires any further configuration you may include
the relevant PPP configuration commands in the file
BOOTCMDS.SYS, which is read by XRPi at boot-up, after it has
finished reading XROUTER.CFG.
Using PPP on Dial-in links
~~~~~~~~~~~~~~~~~~~~~~~~~~
The INTERFACE and PORT should be configured for PROTOCOL=MODEM
as described in the manual section "PSTN Modem Support".
When a logged-in caller issues the command XLINK PPP, XRPi
automatically re-configures the port to support PPP. It then
looks for the file "PPPHOST.n", where n is the port number,
and if found, the PPP configuration commands within the file
are executed. The file may optionally contain NAT
configuration commands if required. The PPPHOST file is
optional. If not present, PPP will be initialised to the
standard defaults.
When the hardware link disconnects (e.g. user says goodbye or
hangs up, link times out, or sysop kills it), the port is
automatically re-configured back to its original MODEM
protocol.
Using PPP on Dial-out links
~~~~~~~~~~~~~~~~~~~~~~~~~~~
The INTERFACE and PORT should be configured for PROTOCOL=MODEM
as described in the manual section "PSTN Modem Support". The
local IP address follows the same rules as the wire-link case
above, but may be overridden temporarily by IPCP commands.
The dialler script (see DUN section) must contain the command
"MODE PPP" plus any required PPP configuration commands. Here
is an extract from a typical connection script:
; Link will use PPP
mode ppp
;
; Configure my authentication username and password
ppp pap user gb7pzt bsfjflavs
;
; Set inactivity timeout to 2 minutes
ppp idle 120
;
; Enable ppp state logging
ppp log 1
;
; Set my (static) IP address for the duration of this call
ppp ipcp local address 194.123.110.4
;
; Now dial the host
send ATDT07979654234
;
etc...
The PPP configuration will persist until the call terminates,
then the port will revert back to MODEM protocol to await the
next incoming or outgoing call.
PPP Configuration Commands
~~~~~~~~~~~~~~~~~~~~~~~~~~
All PPP configuration commands start with "PPP", and are
described in the sysop command reference section. When used
from the command line, or with a BOOTCMDS.SYS file, the first
argument must be a port number. However, PPP commands used
within PPPHOST and dialler scripts *do not* include a port
number, because XRPi knows which port is executing the script.
e.g. at the command line: PPP 3 IDLE 300
in a dialler script: PPP IDLE 300
IP Routing with PPP
~~~~~~~~~~~~~~~~~~~
When a PPP link opens, a route to the peer is automatically
added to XRPi's IP routing table. If the peer indicates that
it knows the addresses of a primary and secondary DNS, those
are added to Xrouter's DNS list.
PPP Logging
~~~~~~~~~~~
PPP system activity can be recorded in file PPPLOG.TXT for
diagnostic purposes. The amount of detail is controlled by
the number specified in the "PPP LOG n" command as
follows:
0 No logging
1 PPP start / stop / timeout events
2 As 1, plus layer up / down events
3 As 2, plus layer start / stop events
4 as 3, plus option accept / reject events
5 as 4, plus hexdump of configuration packets
You are advised against using the higher levels other than on
a temporary basis because they can create very large logfiles.
If logging is in use, you should regularly remove the logfiles
to prevent them growing too large.
SEE ALSO
BOOTCMDS.SYS(8) -- Bootup Configuration Commands File.
DIAL(1) -- Dial a PSTN connection.
DUN(1) -- Dial Up Networking Configuration Commands.
DUN(9) -- Dial-Up Networking.
PPP(1) -- PPP Configuration Commands.
PPPHOST.n(8) -- PPP Configuration File(s)
PSTN(9) -- PSTN Modem Support.
SCRIPT(9) -- Dialer Scripts.
XLINK(1) -- Establish a Temporary SLIP / PPP Interlink.
XROUTER.CFG(8) -- Main Configuration File.