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Command: ppp_manual_setup | Section: 7 | Source: Digital UNIX | File: ppp_manual_setup.7.gz
ppp_manual_setup(7) Miscellaneous Information Manual ppp_manual_setup(7)
NAME
ppp_manual_setup - Describes how to manually set up Point-to-Point Pro-
tocol (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 charac-
teristics of the link. Using PPP, a serial link can be used to trans-
mit Internet Protocol (IP) datagrams, allowing TCP/IP connections be-
tween 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 inter-
face 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 mo-
dem), 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 con-
nect them using telephone line and modems. To use this kind of connec-
tion, 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 pro-
vide 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 authenti-
cating 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 ...] Name of the machine be-
ing authenticated. Name of the machine requiring authentication.
Password or CHAP secret known by both client and server. 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: Login in as root. Save the /vmunix file. Rebuild
the kernel by running the doconfig program and selecting the Point-to-
Point (PPP) option. Copy the new vmunix file to /vmunix. 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. 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 as-
signs addresses and identifies the interface as active. Whether you
run pppd manually on the remote machine or use a script file on the lo-
cal 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 Administra-
tion.
Establishing a PPP Dial-out Connection
To a PPP dial-out connection, do the following: Verify that you can
communicate with the modem. Do the following: Edit the /etc/remote
file and copy the kdebug entry. Modify the new entry, providing a sys-
tem 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. 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 Com-
mand and Shell User's Guide. If your modem is using the AT com-
mand language, enter the following command: AT <Return> If the
modem is not in quiet mode, it responds with an OK message.
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 In-
structions on how to log in and use the remote service
This information is used to create a chat script, which auto-
mates the dial-out process. 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. Edit
the /etc/ppp/options file and include the pppd options as re-
quired 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. Edit the /etc/sys-
log.conf file and do the following: 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.
Add the following entry to the file to create a ppp-log file:
local2.debug /etc/ppp/ppp-log Save the edits
and close the file.
See syslogd(8) for more information. 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. Stop and start syslogd by entering
the following commands: # /sbin/init.d/syslog stop #
/sbin/init.d/syslog start Invoke pppd on the local system to
connect to the remote system. For example, the following com-
mand 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'
Issue the following command to monitor the ppp-log file and de-
termine 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: Set up
your modem for dial-in accss. See modem(7) for more information. 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
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. Issue the init q command
to start the getty process immediately. 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 net-
work setup information and gated.conf(4) for gated options.
Edit the /etc/ppp/options file and include the pppd options re-
quired to support dial-in access for all remote users. See Net-
work 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. 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/pp-
pxx.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. Mc-
Gregor
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 delim off
ppp_manual_setup(7)