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

314 Switching Basics and Intermediate Routing CCNA 3 Labs and Study Guide
Study Guide
Redundant Topologies
Redundancy in a network is required to protect against loss of connectivity due to the failure of an individual
component. However, this provision can result in physical topologies with loops. Physical layer loops
can cause serious problems in switched networks. This section includes exercises to reinforce your understanding
of redundant networks and the unique problem of broadcast storms.
Vocabulary Exercise: Completion
Complete the paragraphs that follow by filling in appropriate words and phrases.
Redundancy allows networks to be fault tolerant, which protects against network downtime. Focusing
specifically on networking, list a few things that can cause network downtime:
Failure of a link
Failure of a port or NIC
Failure of a networking device
Network engineers are often required to balance the cost of redundancy with the need for network availability.
Networks that demand close to 100 percent uptime often strive for “five nines” uptime, a network
that is available 99.999 percent of the time. A goal of redundant topologies is to eliminate network outages
caused by a single point of failure.
However, redundancy in switched topologies introduces a new problem called broadcast storms, which is
when frames loop endlessly through the network, eventually consuming all the available bandwidth.
Concept Questions
List and describe three of the problems that can occur with redundant links and devices in switched or
bridged networks.
■ Broadcast storms—Endless flooding of frames when no loop-avoidance technique is employed.
■ Multiple frame transmission—Multiple copies of unicast frames may cause unrecoverable errors.
■ MAC database instability—Results from copies of the same frame being received on different ports of
the switch.
What mechanism does the IP have to stop packets from endlessly looping throughout an internetwork?
IP uses an 8-bit field called the Time to Live (TTL) that is decremented by each router as the packet travels
from the source to the destination. If this field’s value reaches zero, the packet is dropped. Layer 2 has
no such mechanism.