Karthikeyan Ramasamy

Routing Protocols: Framework and Principles

Routing protocols are mechansims by which routing information is exchanged between routers so that routing decisions can be made. In the Internet, there are three types of routing protocols commonly used. They are: distance vector, link state, and path vector. In this chapter, we present the basic concepts and fundamentals behind each of these three types of protocols in a generic framework. Routing protocols, being distributed mechanisms, can face pitfalls during a transient period such as looping. Thus, we also discuss such issues and how various efforts are made to address them. Steps to translate these protocols to actual routing protocol specifications on the Internet are discussed in later chapters.

IP Packet Filtering and Classification

Packet classification provides a way to discriminate packets and enables many differentiated functionalities. In this chapter, we present how packet classification is accomplished by expressing rules in a classfier. We list the key performance requirements of a packet classification algorithm as the number of memory accesses it needs and the amount of storage it occupies. We then present a number of algorithms that are extensions of trie based algorithms used for IP address lookup. We also outline various approaches for classifying a packet in an arbitrary number of dimensions: divide and conquer, cross-producting, tuple space, and decision tree. We then describe algorithms using each approach. Finally, we conclude the chapter with a discussion of hardware solutions using TCAMs.

IP Traffic Engineering

In this chapter, we discuss traffic engineering for IP intra-domain networks. The role of traffic engineering is to optimize an operational network so that performance requirements are met, yet network resources are well utilized. Traffic engineering is an essential component of IP intra-domain operational networks, especially if the network is large. The main goal of IP traffic engineering is to determine link metrics (weights) in an optimal manner so that the primary goal for the network such as reducing congestion or delay is met through efficient traffic flows. We present multicommodity network flow models with duality for various objectives applicable to IP traffic engineering to show how link weights can be obtained from the dual solution. The models are complemented with small illustrative examples to show weights are obtained.

IP Address Lookup Algorithms

The primary function of routers is to forward packets toward their final destination. To accomplish this, a router must decide for each incoming packet where to send it to next. To do this, the router must do a lookup function to determine the match for the destination address so that it knows which interface to forward the packet to. This chapter describes a number of algorithms that can be used for IP address lookup; their advantages and disavantages are also discussed. Finally, a discussion on hardware-based approaches are also included.

IP Routing and Distance Vector Protocol Family

In this chapter, we start with the basics of IP routing. In doing so, we present how the routing table is formed at routers for IP addresses. We then present the IP distance vector routing protocol family: Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), and Enhanced Interior Gateway Routing Protocol (EIGRP). For each of these protocols, general operations and message formats are presented. Finally, route redistribution between two networks, each using a different routing protool (such as RIP and IGRP), is discussed.

Chapter 6 – OSPF and Integrated IS–IS

In this chapter, we present two important link state routing protocols: Open Shortest Path First (OSPF) and Intermediate System-to-Intermediate System (IS–IS). They are interior gateway protocols (IGPs) used in an autonomous system (AS). They are often deployed by large Internet service providers within their networks. For each of these protocols, general operations and message structures are presented. Their differences are also highlighted.