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slip_manual_setup(7)
NAME
slip_manual_setup - Describes how to manually set up the Serial Line
Internet Protocol (SLIP)
DESCRIPTION
The Serial Line Internet Protocol (SLIP) is a protocol used to run IP over
serial lines, including RS-232 cables connecting two systems and telephone
circuits. Unlike Ethernet, a serial line provides a point-to-point
connection between only two hosts. Like Ethernet, TCP/IP commands (such as
rlogin, ftp, and ping) can be run over the SLIP connection.
Note that although you do not use a network interface with SLIP, 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. Use
the netsetup utility for the initial SLIP configuration. If you need to
change the IP address, see the Changing the IP Address section in this
reference page.
MANAGING ROUTING
You can use either the routed or the gated daemon to manage routing, if you
are not using the SLIP 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: Connections manual and
iprsetup(8).
You should restart the routed or gated process if either was running prior
configuring the SLIP interface with the ifconfig command. This ensures that
the SLIP interface is recognized by the routed or gated daemon.
USING SLIP PHYSICAL CONNECTIONS
You can use SLIP to connect systems either directly (using a null modem) or
over telephone lines using modems.
If you connect the systems directly, use an RS-232 cable to connect the
serial ports on the two hosts. The cable used must be a null modem cable,
such as BC22D-xx, (where xx varies depending on the length of the cable).
You can use this method for hosts in close proximity to each other. 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 BC22E-xx or BC22F-xx and the modems must be set to 8
bit no parity.
MODEMS
SLIP works best when hardware control flow 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 25 pin connectors.
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.
The modems you use with SLIP should be able to handle a baud rate of
38,400. If the modems you plan to use cannot handle a baud rate of 38,400,
you should set them to the highest baud rate to which they can be set. For
example, DEC V32 modems can handle baud rates up to 19,200; however, they
cannot be locked at this baud rate. The highest baud rate they can be set
to is 9,600.
The modems should also be V32bis compliant with V42bis compression.
Alternatively, the modems can support the Microcom Network Protocol (MNP),
because both V42bis and MNP implement a subset of the other protocol.
Use either the tip or kermit command to connect the modem.
Note
Be sure you do not have a getty process running on the port to which
the modem is connected.
To use the tip command, perform the following steps:
1. Add a line such as the following to your /etc/remote file:
REMSYS:dv=/dev/tty00:br#38400:pa=none
In this example:
REMSYS
Is the name of the remote system to which you want to connect.
dv=/dev/tty00
Specifies the tty. Note, if you are running UUCP, tty00 is renamed
to ttyd0.
br#38400
Specifies a baud rate of 38,400.
pa=none
Specifies no parity.
2. Issue the tip command. For example,
prompt> tip REMSYS
If the tip command is successful, you get a connected message.
3. Suspend the process and return to local mode.
If you used the tip command to initiate the connection, issue the
Ctrl/Z key sequence. (If you use Kermit, issue the Ctrl/C followed by
Ctrl/Z key sequence.
4. Enter the slattach command. For example:
prompt> slattach /dev/tty00 38400
5. Use the ping command to wake up the interface on the remote system.
For example:
prompt> ping REMSYS
It may take a few ping messages to wake up the remote interface.
Alternatively, you can leave slattach running on the remote system and rely
on modem passwords and callback for security.
For more information on the tip command, see the tip(1) reference page and
the Command and Shell User's Guide.
SETTING UP SLIP
To configure your system to use SLIP, perform the following steps:
1. Add the SLIP option to the host's kernel.
By default, an entry for SLIP exists in the system configuration file,
/sys/conf/HOSTNAME (where HOSTNAME is the name of your system).
Note
The SLIP option is not included by default on 24 MB configurations
systems. On these systems, you must configure the SLIP option into
the kernel.
The entry appears as follows:
options SL
This entry provides the host with one SLIP interface (sl0). You can
override this option by specifying the nslip parameter in the
/etc/sysconfigtab file. For example, the following example specifies
two SLIP interfaces (sl0 and sl1):
net:
nslip=2
For more information, see the section on configuring the kernel in the
System Administration manual.
2. Add entries to the /etc/hosts file for the network adapters at both
ends of the SLIP network.
For example:
129.34.0.1 sys2_sl sys2_sl.sl.abc.com
129.34.0.2 hst2_sl hst2_sl.sl.abc.com
3. Configure the SLIP interfaces by using the ifconfig command. For
example:
# ifconfig sl0 129.34.0.1 129.34.0.2 netmask 255.255.0.0
On hst2 , you could issue the following command:
# ifconfig sl0 129.34.0.2 129.34.0.1 netmask 255.255.0.0
In these examples, the first argument is the name of the SLIP
pseudodevice, the second argument is the local address of the SLIP
interface, the third argument is the address of the SLIP interface on
the remote host, and the remaining arguments specify the network mask.
For more information, see the ifconfig(8) reference page.
4. Attach a serial line to a SLIP interface by using the slattach
command.
You use the slattach command to select the serial line that will be
attached to the SLIP interface. The slattach command is also used to
enable or disable the SLIP options. For more information on specifying
options, see the slattach(8) reference page.
When you use the slattach command, you do not specify the SLIP
interface to be used (sl0, sl1,...). Instead, the first configured
SLIP interface (one for which you issued an ifconfig command) that is
not already attached is used. You also specify the baud rate for the
serial connection with the slattach command. If you do not specify a
rate, it uses the default rate of 9600 baud. The following is an
example of using the slattach command:
# slattach tty00 9600
In this example, tty00 attaches to a SLIP interface and sets the baud
rate to 9600. The connection will use the options that were previously
set. (When you boot the system, no SLIP options are enabled.)
The following is another example of the slattach command:
# slattach +c -i tty00
In this example, tty00 attaches to a SLIP interface running at 9600
baud (the default speed). TCP header compression is enabled and ICMP
traffic suppression is disabled. (Disabling an option has no effect,
if it was previously disabled.)
For more information on the slattach command, refer to the slattach(8)
reference page.
After completing these steps, the SLIP network is available as long as the
physical connection is ready and the slattach command is running. The ps
command can be used to ensure the slattach command is running. If at any
time the slattach command exits (due to a system or network error), the
command can be executed again to reestablish the SLIP network.
The physical connection is always ready if a direct connection is being
used. For phone connections, the connection is readied by manually dialing
the modem on the local system to connect to the modem on the remote system.
Once the remote modem answers, the data/talk button (or equivalent) should
be pressed to allow the modem on the local host to assume control of the
connection. Depending on the type of modem used, the connection might take
a few seconds while the modems negotiate speeds, protocols, and other
session parameters before it is ready for use. The connection should stay
up until one side hangs up due to some error or a user intentionally
disconnects by pressing the data/talk button.
STOPPING AND RESTARTING SLIP
You stop the SLIP network by using the kill command to stop the running
slattach process that has attached a serial line to SLIP. You can restart
the SLIP network by reissuing the slattach command, which readies the
physical connection. When disabling a SLIP network that runs over a phone
connection, press the data/talk button on the modem to hang up the line.
CHANGING THE IP ADDRESS
To change the IP addresses used on a SLIP interface do the following:
1. Issue the following command to stop the slattach connection:
# kill slattach
2. Issue the ifconfig command to deactivate the interface. For example:
# ifconfig sl0 down
3. Issue the ifconfig command to delete the current local SLIP address.
For example:
# ifconfig sl0 delete 15.141.63.153
4. Issue the ifconfig command to configure the SLIP interface. For
example:
# ifconfig sl0 15.142.63.153 15.143.65.163
In this example, 15.142.63.153 is the local SLIP IP address and
17.143.65.163 is SLIP IP address on the remote system to which you
will connect.
5. Issue the slattach command to attach the serial line to the network
interface.
SEE ALSO
Commands: ifconfig(8), netstat(1)
Network Administration: Connections
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