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OSPF Routing & Network Design
This section prepares you for designing and implementing an OSPF network by providing in-depth, practical coverage of introductory, fundamental, and advanced OSPF topics. This information is conveyed in the following three chapters of the book:
Chapter 4, Introduction to OSPF, covers the background and evolution of the OSPF protocol by tracing the RFCs relating to OSPF. Understanding the functional environment of OSPF is of great importance in order to work within the mechanics of the protocol and design a network in which it will operate properly.
Chapter 5, The Fundamentals of OSPF Routing & Design, covers the fundamentals of OSPF routing and design, including attention to the following topics: OSPF algorithms, OSPF convergence, OSPF design guidelines, area design considerations, OSPF route selection, and OSPF IP addressing and route summarization.
Chapter 6, Advanced OSPF Design Concepts, provides documentation to experienced OSPF network designers on sought-after information, including OSPF redistribution, OSPF on-demand circuit design, OSPF configuration commands, and OSPF error messages.
Introduction to OSPF
Teamwork: If everyone is moving forward together, then the success takes care of itself.Successories
This chapter discusses in detail the background and evolution of the OSPF protocol by tracing the RFCs relating to OSPF. The functional environment of OSPF is of great importance in order to understand the workings of the protocol and design a network in which it will operate properly. As a hierarchical routing protocol, OSPF allows for a variety of different configurations and implementations. This hierarchical ability requires many different levels or areas and they are fully discussed. This chapter covers the following important objectives:
- OSPF Overview. This section discusses the earliest appearance and creation of the shortest path first algorithm. From the established beginnings of OSPF, the evolution and modifications applied to it will be traced through the RFCs. Each RFC relating directly and indirectly to the protocol will be summarized and discussed as needed.
- OSPF Functional Environment. The functional environment is a key element in understanding OSPF. This section discusses and explores several basics to the protocol: network types, router identification, adjacencies, designated routers, protocols within OSPF, and link-state advertisements.
- OSPF Routing Hierarchy. OSPFs capability to perform as a hierarchical routing protocol makes it a good candidate in many large networks. As a result of this capability, OSPF supports a variety of techniques and designations that make operation much smoother. This section discusses the types of OSPF routers and hierarchical design techniques, including how OSPF separates the hierarchy through the use of areas and autonomous systems.
OSPF is a link-state routing protocol. Such protocols are also referred to in literature and technical documents as shortest path first (SPF)-based or distributed database protocols. This section gives a brief description of the developments in link-state technologies that have influenced the evolution of the OSPF protocol.
What is a link state protocol?
OSPF is a link state protocol. You can, for example, 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 its IP address, mask, and the type of network to which it is connected. When you take this information for all the routers in your network, the information is compiled into a link-state database and the SPF algorithm is run against that data. Link state derives from the indication you would receive regarding whether or not the link is up or down.
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.
The Development and Evolution of OSPF
The ARPANET used one of the first distance vector routing protocols, which evolved into RIP, which is still in use today. Serious limitations and problems were encountered with RIP as networks grew. This caused a demand for a new protocol that could run within an autonomous system (AS) and had the capability to grow (scale) to a large-sized network comprised of many routers and network links.
Into this gap stepped OSPF version 1, published as Request for Comments (RFC) 1131 in October 1989 by John T. Moy and the OSPF Working Group. OSPF made use of the famous Dijkstra Algorithm. This algorithm was not new and had not been created specifically to fill the demand of the networking community. In reality, this mathematical formula was initially created to demonstrate the ARMAC computer in 1956, over 30 years before OSPF was ever considered!
Edsger W. Dijkstra was born in 1930 in the city of Rotterdam in the Netherlands. Born into a scientifically oriented family, he quickly excelled and achieved his Ph.D. in Computer Science in 1959 from the University of Amsterdam, Holland. By the time he was 32, he had achieved a full professorship in mathematics at the Eindhoren University. His achievement remains extremely impressive to this day.
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