SLIP (Serial Line Interface Protocol)

About this document
Planning SLIP addresses
Setting up SLIP
Bringing down a SLIP connection
Other notes on SLIP
Information on network address types (classes)

About this document

This document applies to AIX Versions 4.1 and later.

Planning SLIP addresses

One of the most important things to consider when planning your SLIP connection is the addressing. You should examine which address class you wish to use and then develop the actual numerical values. See the section "Information on network address types (classes)" for possible class types.

Please verify that your SLIP addresses do not conflict with any existing (network) addresses on your system. For simplicity, these addresses are used in the following instructions:

   1.1.1.2   for local system  "A" 
   1.1.1.1   for remote system "B"

This SLIP example starts SLIP from the command line. The following instructions add a tty via SMIT and then configure and start SLIP from the command line. It is good to first configure from the command line, as in these instructions, because command line options are easier to correct. After you get SLIP working correctly from the command line, bring it down, detach it to start cleanly, and reconfigure it through SMIT. Configuring it through SMIT will make the configuration permanent and allow SLIP to start automatically at each system reboot.

Setting up SLIP

Step 1: Configure/Add a tty port

Add a tty for a serial port on both machines A and B.

Special notes:

Set flow control to RTS (hardware): NOT Xon
If you are using an 8-wire cable off of a RAN port, set ALTERNATE RJ-45 to ENABLE.
Take note of the baud rate speed, for example 9600. It will be needed later.
Take note of the tty SMIT assigns the port, for example, tty1. It too will be needed later.
Verify that ENABLE LOGIN is set to disable so a getty will not be started on the port.

To add a tty to the system, log on as root or use the su command to become the root user. Then enter smit or smitty on the command line. Select the following order of options from each menu.

#smit

DEVICES

TTY

ADD A TTY

RS232

Select the parent adapter

Select the port number

Remember to set on the tty, the special settings found under "Special Notes" in the preceding section, when you enter the port number.

Step 2: Assign addresses for SLIP

Configure SLIP lines for both systems A and B using selected addresses. Here, 1.1.1.2 is the address for A and 1.1.1.1 is the address for B.

NOTE: sl# should match the tty# being used; that is, if tty1 is being used, sl# should be sl1.

On system A, enter:

       ifconfig  sl#  1.1.1.2   1.1.1.1   up

# equals the same number of the tty you made, for example, tty7 would be sl7.

On system B, enter:

       ifconfig  sl#  1.1.1.1   1.1.1.2   up

# equals the same number of the tty you made, for example, tty7 would be sl7.

Step 3: Verify

Check the status on both machines with the following command line entry:

   ifconfig  sl0

Output should be similar to the following:

sl0: flags=6000031<UP,POINTOPOINT,NOTRAILERS,GROUPRT,64BIT>
        inet 1.1.1.1 --> 1.1.1.2 netmask
0xff000000

Step 4: Make the SLIP connection

On the remote system to be dialed into, enter:

   slattach  tty#

Use the following command line option to dial out of the local system. Replace # with your tty number.

   slattach  tty#  9600  ' "" AT OK ATDT555-3346 CONNECT "" '

In informal terms, the preceding string is interpreted as "Use tty# at 9600 baud, send AT and I should get back an OK, dial 555-3346 and I should get a CONNECT back."

NOTES:

The tty ports MUST be disabled for use with SLIP and not set for share or delay (no getty).
DTR should be set so that the modem tracks the status of DTR and hangs up when a transition from on to off occurs. slattach will bring DTR up. (AT&D2)
CD should be set so the modem tracks the status of DTR (AT&C1).

Test the SLIP connection between system A and system B by using the ping command. On system A, enter:

   ping 1.1.1.1

The system should display packets being sent to and received from that address.

Bringing down a SLIP connection

Enter ps -ef | grep slatt to search for processes associated with SLIP.
WARNING:
Kill these processes WITHOUT the -9 option. The proper way to kill a slattach is with the commandkill <slip pid number>. If SLIP has been defined via SMIT, severe problems could occur if you use kill -9. Problems can affect your system and may cause a crash with LED 888.
Should your system crash with LED 888, a reboot will not correct the problem. Use SMIT to remove the SLIP interface and associated tty. Use SMIT again to reconfigure tty and SLIP.
On the command line, enter ifconfig sl# down where # is the number of your SLIP interface (sl0, sl1, and so on).
To completely remove the SLIP configuration from your system, enter:
```
   ifconfig  sl#  detach 
```
If SMIT was used to add the SLIP line, use SMIT again to remove it. This does not, however, kill the slattach.

Other notes on SLIP

A SLIP connection, when configured from the command line, will stay in effect only until the system is reset or powered down. This is because nothing is permanently added to the system's startup files or the ODM database.
For this reason, experimenting with SLIP on the command line first is recommended. Then, once the configuration is understood, add it through SMIT.
On a SLIP direct connect, no baud rate or dial string is needed. A direct connect is where a serial cable is run directly between two systems. Modems are not involved.
On a SLIP connection over a leased line, no dial string is needed. Leased line is where there is a dedicated phone line between two modems.
Ports must be disabled for SLIP. They cannot be shared or delayed, so a getty is not running on the port.
When slattach is used to link a tty to a SLIP interface, it will take the first available SLIP interface. If more than one exists, a problem might occur during bootup when links to ttys might occur in the wrong order. For example, the right tty may be linked to the wrong interface and vice-versa.
If you cannot ping or access a remote machine, the most likely causes are:
- Incorrect modem or port settings
  A common reason SLIP connects but does not allow ping or other network commands is one or more modems or ttys involved are not using RTS appropriately.
- Malfunctioning cables or phone lines
  Test the connection with ATE or cu by dialing the other system and seeing if you are able to log in. This would be a first test but does not eliminate the chance of port or modem problems. Use IBM cabling or a cable that has adequate shielding.
- Check the modem profile. If the Quiet Enable, or Q value, is set to 1, as with most Hayes compatibles, try changing it to 0 (for example, AT&Q0). If the TD and RD lights flicker when you ping across SLIP, this is likely the problem.
- Incorrect or conflicting network addresses
  Issue the command netstat -i to examine them.
- A port is not set to disable.

Information on network address types (classes)

Network address classes fall into the following ranges:

   Class A:   0   to 128 
   Class B:   128 to 191 
   Class C:   192 to 255

Class A address

   ######.#####.####.### 
     |      |____|____|______ Host Address 
     |_______________________ Network Name

A Class A address consists of an 8-bit network address and a 24-bit local or host address. The first bit in the network address is dedicated to indicating the network class, leaving 7 bits for the actual network address. Since the highest number that 7 bits can represent in binary is 128, there are 128 possible Class A network addresses. Of the 128 possible network addresses, two are reserved for special cases: the network address 127 is reserved for local loopback addresses, and a network address consisting of ones (1s) indicates a broadcast address.

Class B address

   ######.#####.####.### 
      |     |    |____|_______ Host Address 
      |_____|_________________ Network Name

A Class B address consists of a 16-bit network address and a 16-bit local or host address. The first two bits in the network address are dedicated to indicating the network class, leaving 14 bits for the actual network address. Therefore, there are 16,384 possible network addresses and 65,536 local host addresses.

Class C address

   ######.#####.####.### 
      |     |    |    |_______ Host Address 
      |_____|____|____________ Network Name

A Class C address consists of a 24-bit network address and an 8-bit local host address. The first two bits in the network address are dedicated to indicating the network class, leaving 22 bits for the actual network address. Therefore, there are 2,097,152 possible network addresses and 256 possible local host addresses.

Class D address

NOTE: Other systems may support Class D addresses, which are multicast addresses with the highest order bits set to 1-1-1. TCP/IP does not support Class D addresses.

[ Doc Ref: 90605222314632 Publish Date: Apr. 06, 2001 4FAX Ref: 8256 ]

SLIP (Serial Line Interface Protocol)

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