Configuring the Serial Line Internet Protocol (SLIP)
SCO SLIP is a STREAMS-based computer networking
facility that provides for the transmission and reception of
IP packets over serial lines.
SLIP allows the use of TCP/IP networking
applications such as rlogin and telnet over serial lines.
SCO SLIP is an implementation of the Serial Line Internet Protocol
(SLIP) as defined in
RFC 1055 and RFC 1144.
SLIP can be used to connect one host to another via a
single, physical serial line connection between serial ports or
over longer distances using a modem at each end of a telephone line.
A computer that is running SLIP over one or more serial lines
and that is also connected to a computer
network (such as an Ethernet) can serve as a communication gateway between
computers on a network and computers at the far end of each
serial line.
SLIP is an old protocol with a limited number of features.
If you need any of the following features, you should use
PPP
rather than SLIP:
-
support for multiple physical conections within a link (multilink)
-
CHAP or PAP authentication
-
packet filtering
-
error detection
-
negotiation of IP addresses
-
bringup on demand of links
-
automatic reacquisition of links
-
timing out of inactive links
-
extensibility to network protocols other than IP
Configuring SLIP links
To configure a SLIP link
using the Network Configuration Manager:
-
Select
View WAN
and then select
Software Configure SLIP.
-
When presented with a list of currently configured SLIP link
definitions, click on Add to define a new link and
choose the desired type of link configuration:
When you have completed entering details for the link, click on
OK.
If you configure an incoming link,
you will then also be prompted to
enter the SLIP login account's
user ID and password.
To modify the configuration of a link,
highlight it in the list and click on Modify.
Click on OK when you have finished changing the
details of the link's configuration.
To delete a link configuration,
highlight it in the list and click on Delete.
Click on OK when asked to confirm the deletion.
NOTE:
If you modify or delete a link configuration and the link is currently
established, the changes you have made will only take effect when
you next reboot your system.
-
Click on Advanced Options
to configure advanced features
such as header compression.
-
If you need to configure a
Systems(4bnu)
file entry for an outgoing link,
select
Call Services Outgoing.
See
``The Dialup Systems Manager''
for more information.
-
If you need to configure a modem to be used for
an outgoing or an incoming link,
select
Hardware Add WAN device.
For incoming links, configure the serial port to accept incoming
connections and turn on logging in and auto-answer.
Configuring an outgoing link
An outgoing link can be configured to be connected over a
dedicated serial line, or to use the facilities offered by UUCP
to dial up a remote system over a modem and telephone line.
If configured to connect to a system in the UUCP
Systems(4bnu)
file, an outgoing SLIP link allows
the physical equipment, such as a modem and telephone line,
to be shared with other SLIP connections or other
WAN networking services, such as PPP and UUCP.
The remote end of the connection must configure an
incoming link. It must accept the
login and password information forwarded by
UUCP to establish the connection.
Provide the following information
to configure an outgoing link:
UUCP system name-
Enter the name of the entry for the remote system in the
Systems file
if the link will use this to establish UUCP connectivity.
Do not enter a name in this field if you want the system to establish
a SLIP link over a dedicated serial line.
Tty line for SLIP-
Baud rate for tty-
Enter values in these fields if you want the system to establish an
outgoing SLIP link over a dedicated serial line.
Do not enter values in these fields if
the SLIP link will be connected using entries in the
UUCP Systems file.
Local host name-
The name by which the local SLIP interface is known.
Host IP address-
The address by which the local SLIP interface is known.
The remote system must agree to use the specified address or the
local system will refuse to establish the link.
If both a local name and an IP address are entered, the
IP address takes precedence.
Destination name-
The name by which the host at the remote end of the SLIP interface
is known.
Destination IP address-
The IP address for the host at the remote end of the SLIP
interface.
The remote system must agree to use the specified address or the
local system will refuse to establish the link.
If both a destination name and an IP address are entered, the
IP address takes precedence.
Gateway-
If this network interface is not the first on your system, and
you want to be able to forward packets between the different interfaces,
select Yes.
Link configuration information is stored in the file
/etc/inet/slip.start referenced by an entry
in /etc/inet/config. When TCP/IP is started,
the slattach entries in the configuration file
are invoked to create outgoing SLIP links.
Configuring an incoming link
An incoming SLIP link permits the local system to
accept an incoming SLIP connection request from
a remote host.
This type of link requires a login account in
the /etc/passwd file on the local host.
A remote host wishing to initiate a SLIP link with the local
host must use an outgoing type of link, and must specify this
account name and its associated password in the chat script
in the entry for the local system in the remote system's UUCP
Systems(4bnu)
file.
When you use the Network Configuration Manager to configure this
type of link, it creates a SLIP login account
which uses a special shell script instead of a standard shell. The
shell script must execute an slattach
command to establish the SLIP link.
You must configure the remote side to use an outgoing
link type for its end of the link.
Provide the following information
to configure an incoming link:
Login name for SLIP-
The name of the account used to service SLIP sessions.
Login shell script-
The name of the script containing the
slattach command that is used to establish the link.
You must create the login shell script for the user that you name.
The script should be owned by the SLIP user and it must be
executable by them. It
should contain a line to start slattach similar to the following:
/usr/sbin/slattach /dev/term/00 132.147.118.6 132.147.246.12 255.255.0.0 38400 &
In this example, SLIP accepts incoming requests from
the system 132.147.246.12 via the interface 132.147.118.6
on a modem connected to /dev/term/00. The baud rate in this example
is 38400. For more information, see
slattach(1Mtcp).
Advanced SLIP configuration
Advanced configuration of SLIP may be performed
using the Advanced Options available
from the Network Configuration Manager.
Proxy ARP-
If set to On,
add a proxy entry for the IP address of the remote end of
the SLIP link in the ARP table. This will allow
other hosts on the local network to contact the remote system if
its IP address belongs to the local subnet.
TCP/IP header compression-
If set to On,
TCP/IP header compression is enabled and the interface sends
compressed packets. The remote end of the link must be willing
to accept such packets.
Auto detect header compression-
If set to On,
the interface will attempt to detect compressed packets. If it does,
it will respond with compressed packets.
Auto-detection has no effect if TCP/IP header compression is already
configured on.
Hardware flow control-
If set to On, use hardware flow control on the serial line.
ICMP packet suppression-
If set to On, stop ICMP packets
(such as those used for redirects, ping, traceroute,
and router discovery) from passing through the interface.
Maximum transmission unit-
Enter the size of the maximum transmission unit (MTU) in bytes.
The default MTU value is 296. Increasing this value
may increase throughput
as packets can contain more data. However, it may also decrease throughput
if packets are routed through systems with lower MTU values,
as each packet is split (fragmented) into smaller packets for transmission.
You can experiment with this value to obtain the most desirable
results.
NOTE:
The suggested value for the MTU is 40 plus some power of
2. For example, the default value, 296, is 40 plus 2^8.
Other possible values include 552, 1064, and 2088.
Debugging-
If set to On,
enable logging of SLIP debug messages about the state of the link
to the system console.
Deleting all SLIP links
To delete all SLIP link definitions using
the Network Configuration Manager:
-
Select
View WAN
and then select
Software Delete SLIP.
-
When asked if you want to delete all SLIP link definitions,
click on OK.
Administering SLIP
The
slattach(1Mtcp)
command establishes a connection over a
pre-defined SLIP link. Each time slattach is executed,
a new slattach process is created
to control the additional SLIP link in use.
slattach creates a
network interface based on the local and remote IP addresses
that are passed to it as parameters.
Parameters to the slattach command define:
-
the serial communication path for a link by specifying either a tty device
or a UUCP site name (the latter requires the -d option)
-
an IP address for the local side of the communication path and an
IP address for the remote side of the communication path
-
other IP and serial line attributes for the link
Multiple applications (or multiple instances of the same
application) on a local host can communicate with the same remote host using
the same SLIP link.
Use of the same SLIP link requires only that the applications use
the same IP address to specify the remote host.
By using different IP addresses to specify the
same remote host, two applications can also use individual
SLIP links to the same host, provided a separate SLIP link
exists for each remote IP address.
Once a SLIP link is established, it remains active until:
-
you mark the associated SLIP interface down using
ifconfig(1Mtcp).
For example, the command to mark the first SLIP interface down
would be:
ifconfig sl0 down
CAUTION:
Marking an interface down using ifconfig does not remove the link.
Therefore, marking down the interface for an outgoing link
that uses a modem and telephone line does not hang up the line.
The costs of the line usage continue until the link is removed.
-
you kill the associated slattach process to remove
the SLIP interface.
Once a link has been removed, you may need to
remove the associated route from the routing table using the
route(1Mtcp)
command:
route delete destination_address gateway_address
This should only be necessary if the system is not running a routing daemon
such as
routed(1Mtcp).
For more about SLIP
To obtain more information about SLIP
files and commands, consult the following manual pages:
Manual page
|
Information provided
|
slattach(1Mtcp)
|
Command for assigning a tty line to a network interface
|
slip(7tcp)
|
Serial Line Internet Protocol (SLIP) and driver
|
To get more information about SLIP,
see the following Request for Comments (RFCs).
For information on how to obtain RFCs, see
``Obtaining RFCs from the Internet''.
RFC
|
Title
|
1055
|
Nonstandard for transmission of IP datagrams over serial lines: SLIP
|
1144
|
Compressing TCP/IP headers for low-speed serial links
|
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 22 April 2004