Serial Line Internet Protocol (SLIP) is a communication protocol used to connect a computer to the Internet over a serial connection.
When engineers and researchers were first developing TCP/IP networking, they needed a simple communication protocol that could be used to send data between computers linked together by a serial connection. SLIP was the very simple method used to accomplish this.
As Internet connections became more commonplace, and Internet Service Providers (ISP) sprang up offering dial-up Internet connections to the general public, SLIP was also used to establish network connections between ISPs and individual customers. However, this arrangement necessitated a very specifically configured network connection since SLIP lacks the ability to dynamically assign IP addresses.
From its inception, SLIP was never intended to gain wide acceptance as a long-term networking standard. Instead, it was designed to be a short-term stopgap measure while other protocols, such as Point-to-Point Protocol (PPP), were developed to serve the same function.
Frequently Asked Questions
When was SLIP first described in a published specification?
SLIP was first described in the 1988 paper titled A Nonstandard For Transmission of IP Datagrams Over Serial Lines: SLIP. As you can tell from the name of the paper, SLIP was never intended to gain acceptance as the standardized way that TCP/IP network connections are established.
Why was SLIP never formally standardized?
When SLIP was developed and released, work was already underway on more advanced and capable successors, including PPP. Therefore, there was never a reason to standardize SLIP, and the authors intentionally called the paper published in support of SLIP a Nonstandard. Another reason why SLIP was never standardized is that it suffered from several problems that meant that long-term adoption was SLIP would be a very poor choice.
What were some of the problems and limitations of SLIP?
SLIP does not support many of the functions deemed mandatory by modern networks such as error detection, dynamic assignment of IP addresses, or compression of data. In addition, more robust protocols like PPP are actually faster and more reliable, meaning there are very few upsides and noteworthy downsides to using SLIP to establish Internet connections.
What protocol has replaced SLIP?
SLIP has been replaced for nearly all applications by Point-to-Point Protocol (PPP). Initially defined in 1990, PPP development followed close on the heals of SLIP, and supplanted it as the dominant protocol for Internet connections in short order. Today, PPP is used by ISPs to provide dial-up and DSL Internet connections.
The only place SLIP is regularly used today is in microcontrollers, where SLIP's small overhead makes it a preferable protocol for encapsulating IP packets.