Cisco capitulo 1

Chapter 1
Internetworking

TECHNOLOGY
• Describe network communications using layered models
• Compare and contrast key characteristics of LAN environments
• Describe the components of network devices
• Evaluate rules for packet control

• Internetworking basics
• Network segmentation
• How bridges, switches, and routers are used to physically segment anetwork
• How routers are employed to create an internetwork

Internetworking Basics

Before we explore internetworking models and the specifications of the OSI reference model, you’ve got to understand the big picture and learn the answer to the key question, “Why is it so important to learn Cisco internetworking?”

LAN traffic congestion reached overwhelming proportions. Breaking up alarger network into a number of smaller ones is called network segmentation, and it’s accomplished using routers, switches, and bridges
.
Possible causes of LAN traffic congestion are

• Too many hosts in a broadcast domain
• Broadcast storms
• Multicasting
• Low bandwidth
• Adding hubs for connectivity to the network
• A large amount ofARP or IPX traffic (IPX is a Novell routing protocol that is like IP, but really, really chatty)

Even though routers are known for breaking up broadcast domains by default, it’s important to remember that they break up collision domains as well.

Two advantages of using routers in your network are
• They don’t forward broadcasts by default.
• They can filter the networkbased on layer 3 (Network layer) information (i.e., IP address).

Four router functions in your network can be listed as

• Packet switching
• Packet filtering
• Internetwork communication
• Path selection

Switches create separate collision domains, but a single broadcast domain.
Routers provide a separate broadcast domain for each interface.

Theterm bridging was introduced before routers and hubs were implemented, so it’s pretty common to hear people referring to bridges as “switches.” That’s because bridges and switches basically do the same thing—break up collision domains on a LAN

You would use a bridge in a network to reduce collisions within broadcast domains and to increase the number of collision domains in your network.

Doingthis provides more bandwidth for users. And keep in mind that using hubs in your network can contribute to congestion on your Ethernet network.

As always, plan your network design carefully!

The term bridging was introduced before routers and hubs were implemented, so it’s pretty common to hear people referring to bridges as “switches.” That’s because bridges and switches basically do thesame thing—break up collision domains on a LAN

You would use a bridge in a network to reduce collisions within broadcast domains and to increase the number of collision domains in your network.

Doing this provides more bandwidth for users. And keep in mind that using hubs in your network can contribute to congestion on your Ethernet network.
As always, plan your network design carefully!Figure 1.1 shows how a network would look with all these internetwork devices in place.

Remember that the router will not only break up broadcast domains for every LAN interface, but break up collision domains as well.

Although bridges are used to segment networks, they will not isolate broadcast or multicast packets.

Internetworking Models

The OSI model was meant to help vendorscreate interoperable network devices and software in the form of protocols so that different vendor networks could work with each other.

Like world peace, it’ll probably never happen completely, but it’s still a great goal.

The OSI model is the primary architectural model for networks. It describes how data and network information are communicated from an application on one computer, through...