Chapter 5. Ethernet LANs

What You Will Learn

On completing this chapter, you will be able to:

  • List the different Ethernet LAN types

  • Describe the addressing used in Ethernet LANs

  • Describe half-and full-duplex Ethernet LAN operation

  • List the different hardware types found in Ethernet LANs

  • Describe how each hardware device works in an Ethernet LAN

The most widely used local-area network (LAN) access method, defined by the Institute of Electrical and Electronics Engineers (IEEE), is the 802.3 standard. Ethernet has become so popular that most Apple computers and many PCs come with 10/100 Ethernet ports for home use. These ports enable you not just to create a small home network but to connect to the Internet via a Digital Subscriber Line (DSL) or cable modem, which requires an Ethernet connection. A 10/100 port means that the network interface supports both 10BASE-T at 10 megabits per second (Mbps) and 100BASE-T at 100 Mbps.

Ethernet is often a shared-media LAN, which means that all stations on the segment use part of the total bandwidth. Depending on the type of Ethernet implemented, this total bandwidth is a 10 Mbps (Ethernet), 100 Mbps (Fast Ethernet), or 1000 Mbps (Gigabit Ethernet). In a shared Ethernet environment, each device has to contend for network bandwidth using the carrier sense multiple access with collision detect (CSMA/CD) mechanism. In a switched Ethernet environment, each sender and receiver pair has the full bandwidth available for use.

Ethernet LANs use the Media Access Control, or MAC, address to determine how traffic is moved between network segments. Ethernet hubs, defined by the Open System Interconnection (OSI) model physical layer (Layer 1), repeat only the physical signal; the hub does not look at a source or destination address. Ethernet bridges and switches use the source and destination MAC address, defined by the OSI data link layer (Layer 2) to build an interface table and to determine which segment should receive the frame. Routers use the network address, found at the OSI network layer (Layer 3) to build a routing table.

This chapter discusses how the MAC address, the Layer 2 and Layer 3 operations, and the Ethernet hardware fit into an Ethernet LAN environment.