Serial Line Internet Protocol

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Internet protocol suite

5. Application layer

DHCP • DNS • FTP • HTTP • IMAP4 • IRC • MIME • POP3 • SIP • SMTP • SNMP • SSH • TELNET • TLS/SSL • RPC • RTP • SDP • SOAP • …

4. Transport layer

TCP • UDP • RSVP • DCCP • SCTP • …

3. Network layer

IP (IPv4 • IPv6) • ARP • BGP • ICMP • IGMP • IGP • RARP • …

2. Data link layer

ATM • Bluetooth (PAN-Profile) • Ethernet • FDDI • Frame Relay • GPRS • Modems • PPP • Wi-Fi • …

1. Physical layer

Bluetooth RF • Ethernet physical layer • ISDN • Modems • RS232 • SONET/SDH • USB • Wi-Fi • …

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Not to be confused with SLIP programming language.

The Serial Line Internet Protocol (SLIP) is a mostly obsolete encapsulation of the Internet Protocol designed to work over serial ports and modem connections. It is documented in RFC 1055. On PCs, SLIP has been largely replaced by the Point-to-Point Protocol (PPP), which is better engineered, has more features and does not require its IP address configuration to be set before it is established. On microcontrollers, however, SLIP is still the preferred way of encapsulating IP packets due to its very small overhead.

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 either EIA hardware flow control, or CLOCAL mode (3-wire null-modem) UART operation settings.

SLIP does not provide error detection, being reliant on other higher-layer protocols for this. Therefore SLIP on its own is not satisfactory over a particularly error-prone dial-up connection. It is however still useful for testing OS' real-time capabilities under load (by looking at flood-ping statistics).

A version of SLIP with header compression is called CSLIP (Compressed SLIP).