Serial Line Internet Protocol (SLIP)

Definition of Serial Line Internet Protocol (SLIP) in Network Encyclopedia.

What is SLIP (Serial Line Internet Protocol)?

SLIP is an industry-standard protocol developed in 1984 for UNIX environments that supports TCP/IP networking over serial transmission lines. These serial lines are typically dial-up connections using a modem. Serial Line Internet Protocol (SLIP) can provide TCP/IP hosts with dial-up access to the Internet by using SLIP servers located at Internet service providers (ISPs).

SLIP - Serial Line Internet Protocol
SLIP – Serial Line Internet Protocol


SLIP is an older serial line protocol that doesn’t support automatic negotiation of network configurations. It has been largely replaced by the Point-to-Point Protocol (PPP) for the following reasons:

  • SLIP supports only TCP/IP, while PPP is a multiprotocol encapsulation protocol that can also support Internetwork Packet Exchange (IPX) and AppleTalk. This is not an issue, however, if you are connecting to the Internet, which is strictly TCP/IP-based.
  • SLIP generally requires that the host’s TCP/IP parameters be configured manually, while PPP can negotiate the parameters during session establishment. These parameters include the IP address of the host, the window size, and compression.
  • SLIP might require the user to write a script for automating the logon process, while PPP supports both the Password Authentication Protocol (PAP) and the Challenge Handshake Authentication Protocol (CHAP), which let you automatically forward your credentials to the PPP server for authentication.

Microsoft Windows NT and Windows 2000 can function as SLIP clients but not as SLIP servers. Windows NT Remote Access Service (RAS) and Windows 2000 Routing and Remote Access servers cannot accept connections from SLIP clients.