SPF Overview

OSPF is a link-state routing protocol. Such protocols are also referred to in the literature and technical documents as SPF-based or distributed database protocols. This section discusses the developments in link-state technologies that have influenced the evolution of the OSPF protocol.

64 Chapter 2: Introduction to OSPF

What Is a Link-State Protocol?

OSPF is a link-state protocol. For example, you can think of a link as being an interface on the router. The state of the link is a description of that interface. This description would include the interface's IP address and mask, and the type of network to which it is connected. This information is compiled for all the routers in your network into a link-state database, and the SPF algorithm is run against that data. Link-state derives from the indication of a link, in that a link has either an up status or a down status.

The first link-state routing protocol was developed for use in the ARPAnet packet-switching network. This protocol formed the starting point for all other link-state protocols. The homogeneous ARPAnet environment (that is, single-vendor packet switches connected by synchronous serial lines) simplified the design and implementation of the original protocol.

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