opslip

OPSLIP, short for Original SLIP, is a historical protocol used to carry Internet Protocol over serial connections. It is an early variant of the Serial Line Internet Protocol (SLIP) and predates the widespread adoption of PPP. OPSLIP implementations appeared on many UNIX-like systems in the late 1980s and early 1990s, enabling dial-up links over serial lines.

OPSLIP provides basic IP packet framing over a serial link. It uses a simple delimiter to mark packet boundaries and offers no formal link negotiation, encryption, or robust error handling. Configuration was largely manual, with IP addresses and routes set via system utilities, and there was little standardization across implementations.

Limitations of OPSLIP included lack of dynamic addressing, limited support for non-IP protocols, and vulnerability to line noise and framing errors. Its simplicity made it easy to implement but also limited reliability and scalability for growing networks.

Decline and legacy: With the rise of PPP in the mid-to-late 1990s, OPSLIP was gradually phased out in favor of more capable protocols. Today it remains of historical interest, referenced in discussions of early Internet access and in archival documentation. Some vintage systems and emulators may still implement OPSLIP for compatibility with legacy software.

See also: SLIP, PPP, Serial communications.