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Serial Line Internet Protocol (SLIP)

Serial Line Internet Protocol (SLIP) was originally designed for UNIX environments for point-to- point communications between computers, servers, and hosts using TCP/IP. SLIP is used, for example, when a user wants to communicate between a remote home computer and a UNIX/Linux computer that is on a LAN at the office. That user can employ a telephone line, for example, to connect to the UNIX/Linux computer, and then transmit packets using TCP/IP encapsulated within SLIP.

SLIP merely acts as the host WAN protocol, coordinating the connection session over the telephone wire and modems. After the protocol (with its data payload) reaches the destination, the SLIP header and trailer are removed, leaving TCP/IP.

Older Remote Communications Protocol

Note that SLIP is an older remote communications protocol with more overhead than PPP (discussed in the next section). Compressed Serial Line Internet Protocol (CSLIP) is a more recent extension of SLIP that compresses header information in each packet sent across a remote link. CSLIP reduces the overhead of a SLIP connection by decreasing the header size and thus increasing the speed of communications. However, the header still must be decompressed at the receiving end.

No Network Connect Authentication

Both SLIP and CSLIP are limited in that they do not support network connection authentication to prevent someone from intercepting a communication. They also do not support automatic setup of the network connection at multiple OSI layers at the same time for a faster connection. Another disadvantage is that SLIP and CSLIP are intended for asynchronous communications, as found, for example, in a modem-to-modem connection. They do not support synchronous connections, such as the creation of a connection strictly through the Internet from a modem to an ISP.

Note: Many dial-up or remote communication services do not support SLIP or CSLIP because these protocols do not provide authentication. In addition, because of the lack of security, use SLIP only if necessary when the computer operating system you are configuring does not support PPP.


Published on Thu 21 March 2002 by Daisy Batty in Networking with tag(s): slip