NAME
sl —
Serial Line IP (SLIP) network
interface
SYNOPSIS
pseudo-device sl
DESCRIPTION
Thesl 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 This is why SLIP has been superseded by the Point-to-Point Protocol (PPP), which does all of those things, and much more.