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Ebook Ethernet networks (4th edition): Part 2

(BQ) Part 2 book "Ethernet networks" has contents: Bridging and switching methods and performance issues, routers, wireless ethernet, managing the network, the future of ethernet, security. | Ethernet Networks: Design, Implementation, Operation, Management. Gilbert Held Copyright 2003 John Wiley & Sons, Ltd. ISBN: 0-470-84476-0 chapter six Bridging and Switching Methods and Performance Issues In Chapter 5, an overview of bridge operations was presented, along with information concerning the functionality of other local area network hardware and software components. That chapter deferred until now a detailed examination of bridging methods, to include their network use and performance issues. In this chapter, we will focus our attention on those issues, examining different methods that bridges use for routing frames, performance issues that govern their ability to examine and forward frames without introducing network bottlenecks, and their typical employment for interconnecting LANs. Because LAN switches represent a special type of multiport bridge, we will also focus our attention upon this topic later in this chapter. Thus, once we have an appreciation for the operation and utilization of bridges, we will turn our attention to LAN switches. 6.1 Bridging Methods Bridges operate by examining MAC layer addresses, using the destination and source addresses within a frame as a decision criterion to make their forwarding decisions. Operating at the MAC layer, bridges are not addressed, and must therefore examine all frames that flow on a network. Because bridges operate at the MAC layer, they in effect terminate a collision domain. That is, if a collision is detected upon one port of a bridge, it is not propagated onto any output port. This means that, unlike a repeater, a bridge can be used to extend the span of a LAN. 279 280 chapter six Address Issues Since bridges connect networks, it is important to ensure that duplicate MAC addresses do not occur on joined internal networks — a topology we will refer to as an intranet. While duplicate addresses will not occur when universally administered addressing is used, when locally administered .