NAME
sl —
Serial Line IP (SLIP) network
interface
SYNOPSIS
pseudo-device sl
DESCRIPTION
The
sl interface allows asynchronous serial lines to be used
as IPv4 network interfaces using the SLIP protocol.
To use the
sl interface, the administrator must first create
the interface and assign a tty line to it. The
sl interface
is created using the
ifconfig(8)
create subcommand, and
slattach(8) is used to assign
a tty line to the interface. Once the interface is attached, network source
and destination addresses and other parameters are configured via
ifconfig(8).
The
sl interface can use Van Jacobson TCP header compression
and ICMP filtering. The following flags to
ifconfig(8) control these
properties of a SLIP link:
-
-
- link0
- Turn on Van Jacobson header compression.
-
-
- -link0
- Turn off header compression. (default)
-
-
- link1
- Don't pass through ICMP packets.
-
-
- -link1
- Do pass through ICMP packets. (default)
-
-
- link2
- If a packet with a compressed header is received,
automatically enable compression of outgoing packets. (default)
-
-
- -link2
- Don't auto-enable compression.
DIAGNOSTICS
- sl%d: af%d not supported.
- The interface was handed a message with addresses
formatted in an unsuitable address family; the packet was dropped.
SEE ALSO
inet(4),
intro(4),
ppp(4),
strip(4),
ifconfig(8),
slattach(8),
sliplogin(8),
slstats(8)
J. Romkey, A
Nonstandard for Transmission of IP Datagrams over Serial Lines: SLIP,
RFC, 1055,
June 1988.
Van Jacobson,
Compressing TCP/IP Headers for Low-Speed Serial
Links, RFC, 1144,
February 1990.
HISTORY
The
sl device appeared in
NetBSD 1.0.
BUGS
SLIP can only transmit IPv4 packets between preconfigured hosts on an
asynchronous serial link. It has no provision for address negotiation,
carriage of additional protocols (e.g. XNS, AppleTalk, DECNET), and is not
designed for synchronous serial links. This is why SLIP has been superseded by
the Point-to-Point Protocol (PPP), which does all of those things, and much
more.