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CCNA Certification All-In-One For Dummies by Silviu Angelescu

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Chapter 1: Introducing Layer 2 Switches

Exam Objectives

Describing data link OSI Layer 2 and how it relates to Layer 2 switches

Describing the purpose of a Layer 2 switch

Differentiating a Layer 2 switch from a hub or a bridge

Describing the basic Layer 2 switch functions

Managing Layer 2 switch port security

Describing how a Layer 2 switch handles unicast, multicast, and broadcast transmissions

Describing MAC address table thrashing and broadcast storms

Read this chapter to find out about Layer 2 switches.

Layer 2 — Data Link Layer Review

Layer 2 in the Open Systems Interconnection (OSI) and TCP/IP network models is the data link layer. The data link layer transmits data on the physical medium. The data link layer uses physical addresses assigned to each physical network device in the local network to route data from one physical device to another. These addresses are called Media Access Control (MAC) addresses in TCP/IP. MAC addresses uniquely identify a specific network device, such as a switch or a router, or a network interface card (NIC), in a host device.

The data link layer has the following features:

Receives each packet from the network layer on the sending host

Wraps up the packet in a data frame along with local routing data (the physical MAC address)

Sends the data frame to the physical layer to code an electrical or optical signal

The physical layer transmits the data frame over a wire or over the air (wireless transmission).

On the receiving host, the data ...

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