CCNA (R & S) Module 03 - Routing & Switching Essentials - Chapter 4

© 2008 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 1
Chapter 4: Switched
Networks
Routing and Switching Essentials v6.0

4.1 LAN Design

Presentation_ID 3© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Converged Networks
Growing Complexity of Networks
 Our digital world is
changing.
 Information must be
accessed from
anywhere in the
world.

Converged Networks
Elements of a Converged Network
 To support collaboration, networks
employ converged solutions.
 Data services include voice systems, IP
phones, voice gateways, video support,
and video conferencing.
 Call control, voice messaging, mobility,
and automated attendant are also
common features.
 Multiple types of traffic; only one network
to manage.
 Substantial savings over installation and
management of separate voice, video,
and data networks.
 Integrates IT management.

Converged Networks
Cisco Borderless Networks
 A network architecture
that allows organizations
to connect anyone,
anywhere, anytime, and
on any device securely,
reliably, and seamlessly.
 Designed to address IT
and business challenges,
such as supporting the
converged network and
changing work patterns.

Converged Networks
Hierarchy in the Borderless Switched Network
Borderless switched network
design guidelines are built
upon the following principles:
 Hierarchical
 Modularity
 Resiliency
 Flexibility

Converged Networks
Access, Distribution, and Core Layers

Switched Networks
Role of Switched Networks
 Switching technologies are
crucial to network design.
 Switching allows traffic to
be sent only where it is
needed in most cases,
using fast methods.
 A switched LAN:
 Allows more flexibility
 Allows more traffic
management
 Supports quality of service,
additional security, wireless,
IP telephony, and mobility
services

Switched Networks
Form Factors
Fixed
Configuration
Switches

Switched Networks
Form Factors
Modular
Platform

Switched Networks
Form Factors
Stackable
Configuration
Switches

4.2 The Switched Environment

Frame Forwarding
Switching as a General Concept in Networking and
Telecommunications
 A switch makes a decision based on ingress and a destination port.
 A LAN switch keeps a table that it uses to determine how to forward
traffic through the switch.
 Cisco LAN switches forward Ethernet frames based on the
destination MAC address of the frames.

Frame Forwarding
Dynamically Populating a Switch MAC Address
Table
 A switch must first learn which devices exist on each port before it
can transmit a frame.
 As a switch learns the relationship of ports to devices, it builds a table
called a MAC address or content addressable memory (CAM) table.
 CAM is a special type of memory used in high-speed searching
applications.
 The information in the MAC address table is used to send frames.
 When a switch receives an incoming frame with a MAC address that
is not found in the CAM table, it floods it to all ports, except the one
that received the frame.

Frame Forwarding
Switch Forwarding Methods

Frame Forwarding
Store-and-Forward Switching
 Allows the switch to:
 Check for errors
(via FCS check)
 Perform automatic
buffering
 Slower forwarding
process

Frame Forwarding
Cut-Through Switching
 Allows the switch to
start forwarding in
about 10
microseconds
 No FCS check
 No automatic
buffering

Switching Domains
Collision Domains
Ethernet switch port:
 Operating in half
duplex, each segment
is in its own collision
domain.
 Operating in full duplex
eliminates collisions.
 By default, will auto-
negotiate full duplex
when the adjacent
device can also
operate in full duplex.
Collision domain - Segment where devices compete to communicate.

Switching Domains
Broadcast Domains
A broadcast domain is the extent of the network where a broadcast
frame can be heard.
 Switches forward broadcast frames to all ports; therefore, switches
do not break broadcast domains.
 All ports of a switch, with its default configuration, belong to the same
broadcast domain.
 If two or more switches are connected, broadcasts are forwarded to
all ports of all switches, except for the port that originally received the
broadcast.

Switching Domains
Alleviating Network Congestion
Switches help alleviate network congestion by:
 Facilitating the segmentation of a LAN into separate collision
domains.
 Providing full-duplex communication between devices.
 Taking advantage of their high-port density.
 Buffering large frames.
 Employing high-speed ports.
 Taking advantage of their fast internal switching process.
 Having a low, per-port cost.

4.3 Chapter Summary

 The trend in networks is towards convergence using a single set of wires and devices to
handle voice, video, and data transmission.
 There has been a dramatic shift in the way businesses operate.
 There are no physical offices or geographic boundaries constraints. Resources must now
be seamlessly available anytime and anywhere.
 The Cisco Borderless Network architecture enables different elements, from access
switches to wireless access points, to work together and allow users to access resources
from any place, at any time.
 The traditional, three-layer hierarchical design model divides the network into core,
distribution, and access layers, and allows each portion of the network to be optimized for
specific functionality.
 It provides modularity, resiliency, and flexibility, which provides a foundation that allows
network designers to overlay security, mobility, and unified communication features.
 Switches use either store-and-forward or cut-through switching.
 Every port on a switch forms a separate collision domain allowing for extremely high-
speed, full-duplex communication.
 Switch ports do not block broadcasts and connecting switches can extend the size of the
broadcast domain, often resulting in degraded network performance.
Chapter Summary
Summary

CCNA (R & S) Module 03 - Routing & Switching Essentials - Chapter 4

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