1.\" $NetBSD: sl.4,v 1.17 2020/01/19 01:25:03 thorpej Exp $ 2.\" 3.\" Copyright (c) 1983, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" From: @(#)lo.4 8.1 (Berkeley) 6/5/93 31.\" 32.Dd January 18, 2020 33.Dt SL 4 34.Os 35.Sh NAME 36.Nm sl 37.Nd Serial Line IP (SLIP) network interface 38.Sh SYNOPSIS 39.Cd pseudo-device sl 40.Sh DESCRIPTION 41The 42.Nm 43interface allows asynchronous serial lines to be used as 44.Tn IPv4 45network interfaces using the 46.Tn SLIP 47protocol. 48.Pp 49To use the 50.Nm 51interface, the administrator must first create the interface and assign 52a tty line to it. 53The 54.Nm 55interface is created using the 56.Xr ifconfig 8 57.Cm create 58subcommand, and 59.Xr slattach 8 60is used to assign a tty line to the interface. 61Once the interface is attached, network source and destination addresses and 62other parameters are configured via 63.Xr ifconfig 8 . 64.Pp 65The 66.Nm 67interface can use Van Jacobson 68.Tn TCP 69header compression and 70.Tn ICMP 71filtering. 72The following flags to 73.Xr ifconfig 8 74control these properties of a SLIP link: 75.Bl -tag -width Ar 76.It Ar link0 77Turn on Van Jacobson header compression. 78.It Ar -link0 79Turn off header compression. (default) 80.It Ar link1 81Don't pass through ICMP packets. 82.It Ar -link1 83Do pass through ICMP packets. (default) 84.It Ar link2 85If a packet with a compressed header is received, automatically enable 86compression of outgoing packets. (default) 87.It Ar -link2 88Don't auto-enable compression. 89.El 90.Sh DIAGNOSTICS 91.Bl -diag 92.It sl%d: af%d not supported . 93The interface was handed 94a message with addresses formatted in an unsuitable address 95family; the packet was dropped. 96.El 97.Sh SEE ALSO 98.Xr inet 4 , 99.Xr intro 4 , 100.Xr ppp 4 , 101.Xr ifconfig 8 , 102.Xr slattach 8 , 103.Xr sliplogin 8 , 104.Xr slstats 8 105.Rs 106.%A J. Romkey 107.%R RFC 108.%N 1055 109.%D June 1988 110.%T "A Nonstandard for Transmission of IP Datagrams over Serial Lines: SLIP" 111.Re 112.Rs 113.%A Van Jacobson 114.%R RFC 115.%N 1144 116.%D February 1990 117.%T "Compressing TCP/IP Headers for Low-Speed Serial Links" 118.Re 119.Sh HISTORY 120The 121.Nm 122device appeared in 123.Nx 1.0 . 124.Sh BUGS 125.Tn SLIP 126can only transmit 127.Tn IPv4 128packets between preconfigured hosts on an asynchronous serial link. 129It has no provision for address negotiation, 130carriage of additional protocols (e.g. 131.Tn XNS , 132.Tn AppleTalk , 133.Tn DECNET ) , 134and is not designed for synchronous serial links. 135This is why 136.Tn SLIP 137has been superseded by the Point-to-Point Protocol 138.Pq Tn PPP , 139which does all of those things, and much more. 140