CCNA 3 Labs and Study Guide - BINARYBB.INFO – @jagalbraith

Introduction to LAN Switching
In the past, repeaters were used in most Ethernet networks. Because Ethernet is a broadcast topology,
adding repeaters enlarged the domain in which collisions can occur causing a reduction in the bandwidth
available for data transfer. Bridges were soon introduced to create multiple collision domains. Bridges
evolved into switches capable of microsegmenting a LAN, effectively creating a collision-free environment.
Many modern switches are capable of performing varied and complex tasks in the network. For example,
some switches are capable of performing both Layer 2 and Layer 3 functions. The exercises in this section
focus on how a switch or router makes a decision to forward data on its way to the intended destination.
This section provides an introduction to network segmentation and describes the basics of switch operation.
Vocabulary Exercise: Completion
Directions: Complete the paragraphs that follow by filling in appropriate words and phrases.
Networks can be divided into smaller units by a bridge or a switch. These smaller units are called segments.
Each unit is its own collision domain.
Bridges and switches are Layer 2 devices that forward data frames based on the MAC address. Bridges
read the source MAC address of the data packets to discover the devices that are on each segment. The
source MAC address is used to populate the MAC address table.
Bridges and switches provide segmentation within a single network or subnetwork. Routers provide connectivity
between networks and subnetworks. Routers do not forward broadcasts, whereas switches and
bridges do forward broadcast frames.
When a switch or bridge is first initialized, the MAC address table is empty. With an empty MAC address
table, the switch or bridge must forward each frame to all connected ports other than the one on which the
frame arrived. Sending a frame out all connected ports except the incoming port is called flooding the
frame. Once a switch or a bridge has learned the topology, it can stop frames from propagating onto segments
where the destination does not exist. This process is called filtering.
Building the MAC Address Table Exercise
Assume that the bridge in Figure 4-3 was just installed and powered on. The MAC address table is empty.
Answer the following questions and complete the table as the bridge would build it.
Figure 4-3 Building the MAC Address Table
A
0260.8c01.1111
0260.8c01.2222
E0
E1
Chapter 4: Switching Concepts 225
C
0260.8c01.3333
B D
0260.8c01.4444