slip_manual_setup(7)slip_manual_setup(7)NAMEslip_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 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. Use the netsetup utility for the initial SLIP configura‐
tion. 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 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 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 pro‐
tocol.
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: Add a line such as
the following to your /etc/remote file:
REMSYS:dv=/dev/tty00:br#38400:pa=none
In this example: Is the name of the remote system to which you
want to connect. Specifies the tty. Note, if you are running
UUCP, tty00 is renamed to ttyd0. Specifies a baud rate of
38,400. Specifies no parity. Issue the tip command. For exam‐
ple, prompt> tip REMSYS
If the tip command is successful, you get a connected message.
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. Enter the slattach command.
For example: prompt> slattach /dev/tty00 38400 Use the ping com‐
mand to wake up the interface on the remote system. For exam‐
ple: 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: 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 configura‐
tions 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. 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 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 spec‐
ify the network mask.
For more information, see the ifconfig(8) reference page.
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 config‐
ured SLIP interface (one for which you issued an ifconfig com‐
mand) 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 slat‐
tach(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 net‐
work.
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 read‐
ies 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:
Issue the following command to stop the slattach connection: # kill
slattach Issue the ifconfig command to deactivate the interface. For
example: # ifconfig sl0 down Issue the ifconfig command to delete the
current local SLIP address. For example: # ifconfig sl0 delete
15.141.63.153 Issue the ifconfig command to configure the SLIP inter‐
face. 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. Issue the slattach command to attach the
serial line to the network interface.
SEE ALSO
Commands: ifconfig(8), netstat(1)
Network Administration: Connections
slip_manual_setup(7)
