slip_manual_setup - Describes how to manually set up the Serial Line Internet Protocol (SLIP)
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.
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 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.
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 Digital 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 Digital BC22E-xx or BC22F-xx and the modems must be set to 8 bit no parity.
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.
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.
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 example, prompt> tip REMSYS If the tip command is successful, you get a connected message. Suspend the process and return to local mode.
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.
To configure your system to use SLIP, perform the following steps: Add the SLIP option to the host's kernel.
# 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.)
# 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.)
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.
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.
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 126.96.36.199 Issue the ifconfig command to configure the SLIP interface. For example: # ifconfig sl0 188.8.131.52 184.108.40.206 In this example, 220.127.116.11 is the local SLIP IP address and 18.104.22.168 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.
Commands: ifconfig(8), netstat(1)
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