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SL(4)                        Device Drivers Manual                       SL(4)

     sl - Serial Line IP (SLIP) network interface

     pseudo-device sl

     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

     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.

     -link2        Don't auto-enable compression.

     sl%d: af%d not supported.  The interface was handed a message with
     addresses formatted in an unsuitable address family; the packet was

     inet(4), intro(4), ppp(4), ifconfig(8), slattach(8), sliplogin(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.

     The sl device appeared in NetBSD 1.0.

     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     superseded by the Point-to-Point Protocol (PPP), which does all of those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.

NetBSD 10.99                   January 18, 2020                   NetBSD 10.99