(SLIP) Software allowing the Internet Protocol (IP), normally used on Ethernet, to be used over a serial line, e.g. an EIA-232 serial port connected to a modem. It is defined in RFC 1055.

SLIP modifies a standard Internet datagram by appending a special SLIP END character to it, which allows datagrams to be distinguished as separate. SLIP requires a port configuration of 8 data bits, no parity, and EIA or hardware flow control. SLIP does not provide error detection, being reliant on other high-layer protocols for this. Over a particularly error-prone dial-up link therefore, SLIP on its own would not be satisfactory.

A SLIP connection needs to have its IP address configuration set each time before it is established whereas Point-to-Point Protocol (PPP) can determine it automatically once it has started.

See also SLiRP.