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ppp_manual_setup(7)
NAME
ppp_manual_setup - Describes how to manually set up Point-to-Point Protocol
(PPP) connections
DESCRIPTION
The Point-to-Point Protocol (PPP) provides a standard way to transmit IP
datagrams over a serial link and a standard way for the systems (peers) at
either end of the link to negotiate various optional characteristics of the
link. Using PPP, a serial link can be used to transmit Internet Protocol
(IP) datagrams, allowing TCP/IP connections between the peers.
Note that although you do not use a network interface with PPP, you must
have a network interface configured on your system for the network daemons
(such as nfsd and rwhod) to run properly. The network interface must be
configured with a new IP address. For example, if you have a personal
computer that you use at home and in the office, do not use the same IP
address for the network interface at home as you use in the office.
Managing Routing
You can use the gated daemon to manage routing, if you are not using the
PPP connection solely to communicate between the two systems making the
connection.
If you plan to use a system as an IP router, it must be configured to allow
the forwarding of IP packets. For more information on setting a system up
as an IP router, see the Network Administration manual and iprsetup(8).
PPP Physical Connections
You can connect systems either directly to each other (using a null modem),
if they are in close proximity, or over telephone lines using modems, if
they are not.
If you connect the systems directly, use a null modem cable, such as
Digital BC22D-xx (where xx varies depending on the length of the cable) to
connect the serial ports on the two hosts. The maximum length of this type
of connection is defined by the RS-232 standard.
If the systems are not in close proximity to each other, you can connect
them using telephone line and modems. To use this kind of connection,
attach a modem to a serial port on both hosts so that the two hosts can
establish a serial connection between them. You can use an RS-232 cable
connected to the serial port on the host. This cable must be a straight-
through cable such as Digital BC22E-xx or BC22F-xx and the modems must be
set to 8 bit, no parity.
Modems
PPP works best when hardware flow control is used. High speed modems often
fall-back to a lower data rate when line degradation occurs. To support
hardware flow control you must use cables with a sufficient number of wires
for full modem control. DECconnect cables do not provide a sufficient
number of wires. Therefore, do not use them. See modem(7) for a list of
modem cables to use and modem guidelines.
Note
Do not use XON/XOFF flow control. It will corrupt the data stream
causing the TCP layer over IP to issue retransmit requests for over-
runs.
Authentication
PPP provides two protocols for authenticating hosts and for authenticating
your host system to others:
· Password Authentication Protocol (PAP)
· Cryptographic Authentication Protocol (CHAP)
Both protocols exchange secrets in order to complete the authentication
process. PAP secrets are contained in the /etc/ppp/pap-secrets file; CHAP
secrets are contained in the /etc/ppp/chap-secrets file. Only root should
be able to read these files. Both files have the following format:
[client server secret[ip_address ...]
client
Name of the machine being authenticated.
server
Name of the machine requiring authentication.
secret
Password or CHAP secret known by both client and server.
ip_address ...
Zero or more IP addresses that the client may use (this field is used
only on the server).
See Network Administration for information on authentication.
Verifying PPP Support in the Kernel
Verify that PPP is supported in the kernel by entering the following
command:
# sysconfig -s | grep ppp
If it is not loaded and configured, do the following:
1. Login in as root.
2. Save the /vmunix file.
3. Rebuild the kernel by running the doconfig program and selecting the
Point-to-Point (PPP) option.
4. Copy the new vmunix file to /vmunix.
5. Edit the /etc/sysconfigtab file amd add the following lines:
ppp:
nppp=2
This provides for 2 PPP connections (ppp0 and ppp1). If your system
requires a greater number of PPP connections, increase the number.
For more information, see the section on configuring the kernel in the
System Administration manual.
6. Reboot the system
PPP Connections
A PPP connection between two systems involves setting up a serial link and
running the PPP daemon, pppd, on both ends of the link. Guidelines for
running pppd are as follows:
· If you want the local address of the PPP link to differ from the IP
address for the local host's Ethernet or other broadcast interface,
putthe desired address on the pppd command line with a colon appended
as follows:
local_addr:
· Do not use ifconfig to configure the addresses of the PPP interface.
The pppd daemon assigns addresses and identifies the interface as
active.
· Whether you run pppd manually on the remote machine or use a script
file on the local machine to run pppd on the remote machine, do not
provide a device name to pppd; it uses the controlling tty by default.
For information on pppd options, see pppd(8) and Network Administration.
Establishing a PPP Dial-out Connection
To a PPP dial-out connection, do the following:
1. Verify that you can communicate with the modem. Do the following:
a.
Edit the /etc/remote file and copy the kdebug entry.
b.
Modify the new entry, providing a system name for the entry, the
correct DIGITAL UNIX device (tty00 or tty01 depending on your
system), the correct baud rate, and correct parity. See remote(4)
for more information.
c.
Use the tip command to access the modem as follows:
% tip system_name
system_name is the system name from the /etc/remote file.
Note
Be sure you do not have a getty process running on the port to
which the modem is connected.
For more information on the tip command, see tip(1) and the Command
and Shell User's Guide.
d.
If your modem is using the AT command language, enter the following
command:
AT <Return>
If the modem is not in quiet mode, it responds with an OK message.
2. Contact the remote system administrator or your Internet Service
Provider (ISP) and obtain the following information:
·
Your remote IP address and netmask, unless the remote system assigns
the IP address dynamically
·
Characters that might need to be escaped
·
Instructions on how to log in and use the remote service
This information is used to create a chat script, which automates the
dial-out process.
3. Create a file for commands that the hat program uses to direct the
modem what number to dial and what to send the remote system in order
to start pppd. This file is called a chat script. Each entry in a
chat script has the following format:
[string_chat_expects string_chat_sends]
See chat(8) for more information on chat and chat scripts.
4. Edit the /etc/ppp/options file and include the pppd options as
required by the remote system or ISP. See pppd(8) for a complete list
of pppd options. See Network Administration for a sample
/etc/ppp/options file for dial-out access.
5. Edit the /etc/syslog.conf file and do the following:
a.
Add the local2 facility (used by pppd and chat) to the line that
specifies /dev/console as the message destination as follows:
kern.debug;local2.notice /dev/console
In this example, the notice level is specified.
b.
Add the following entry to the file to create a ppp-log file:
local2.debug /etc/ppp/ppp-log
c.
Save the edits and close the file.
See syslogd(8) for more information.
6. Create the ppp-log file by issuing the following command:
# touch /etc/ppp/ppp-log
This file must be created before the next step to ensure that PPP
event logging is started.
7. Stop and start syslogd by entering the following commands:
# /sbin/init.d/syslog stop
# /sbin/init.d/syslog start
8. Invoke pppd on the local system to connect to the remote system. For
example, the following command starts a link on tty01 and specifies
the connect option to run the chat program using the specified chat
script file.
% pppd /dev/tty01 38400 connect 'chat -v -f /etc/ppp/chat-script'
9. Issue the following command to monitor the ppp-log file and determine
whether the PPP connection is active:
% tail -f /etc/ppp/ppp-log
If any problems occur while using PPP, see the Network Administration
manual.
Establishing a Dial-In Connection
To configure a PPP dial-in system, complete the following steps:
1. Set up your modem for dial-in accss. See modem(7) for more
information.
2. Edit the /etc/passwd file and create a dedicated entry for a PPP user.
For the login shell field, specify /usr/sbin/startppp; for example:
ppp1:password:10:20:Remote PPP User:/usr/users/guest:/usr/sbin/startppp
3. Edit the /etc/inittab file and create an entry for each terminal
device that is to run PPP. For example:
modem:3:respawn:/usr/sbin/getty /dev/tty00 M38400 vt100
See inittab(4) for more information.
4. Issue the init q command to start the getty process immediately.
5. If the dial-in system is going to be a gateway for the dial-out system
to reach other systems on the LAN, the dial-in system must be
configured as an IP router and must also run gated. Edit the
/etc/gated.conf file and delete the nobroadcast option (if specified)
in the rip statement. See the Network Administration manual for basic
network setup information and gated.conf(4) for gated options.
6. Edit the /etc/ppp/options file and include the pppd options required
to support dial-in access for all remote users. See Network
Administration for a sample /etc/ppp/options file for dial-in access.
If you want to specify options for each individual serial port, create
a /etc/ppp/options.ttyxx file and include the remote IP address and
any other options that apply to that specific serial port. See
pppd(8) for a complete list of pppd options.
7. After an incoming call is received and a connection established,
startppp runs in the background. The process ID is logged in the
/etc/ppp/pppxx.pid file.
If any problems occur while using PPP, see the Network Administration
manual.
Stopping and Restarting PPP
To terminate the PPP link, send a TERM or INTR signal to one of the pppd
daemons by issuing the following command:
# kill `cat /etc/ppp/pppxx.pid`
In this command, pppxx specifies the pppd used for the PPP connection. The
pppd specified in the command also instructs other pppd daemons to
terminate.
If pppd is attached to a hardware serial port that is connected to a modem,
the daemon should gev a HUP signal when the modem hangs up, which will
cause it to clean up and exit. This action depends on the driver and its
current settings.
RELATED INFORMATION
Files: gated.conf(4), inittab(4), remote(4).
Commands: tip(1), chat(8), iprsetup(8), pppd(8), syslogd(8).
Networks: modem(7).
Network Administration
RFC 1332, "The PPP Internet Protocol Control Protocol (IPCP)", G. McGregor
RFC 1334, "PPP Authentication Protocols", B. Lloyd, W. Simpson
RFC 1661, "The Point-to-Point Protocol (PPP)", W. Simpson
RFC 1662, "PPP in HDLC-like Framing", W. Simpson