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Chapter 2

Layer-2 Switching

wiring to the corporate backbone, and was then connected to a router. PCs
ran an emulating software program that allowed them to connect to the
mainframe services, giving those PCs the ability to access services from
the mainframe and LAN simultaneously. Eventually the PC became robust
enough to allow application developers to port applications more effectively
than they could ever before--an advance that markedly reduced networking
prices and enabled businesses to grow at a much faster rate.

When Novell became more popular in the late 1980s and early 1990s,

O/S 2 and LAN Manager servers were by and large replaced with NetWare
services. This made the Ethernet network even more popular, because that's
what Novell 3.

servers used to communicate with client/server software.

So that's the story about how the network in Figure 2.1 came into being.

There was only one problem the corporate backbone grew and grew, and as
it grew, network services became slower. A big reason for this was that, at
the same time this huge burst in growth was taking place, LAN services
needed even faster service, and the network was becoming totally saturated.
Everyone was dumping the Macs and dumb terminals used for the main-
frame service in favor of those slick new PCs so they could more easily
connect to the corporate backbone and network services.

All this was taking place before the Internet's momentous popularity

(Al Gore was still inventing it?), so everyone in the company needed to access
the corporate network's services. Why? Because without the Internet, all
network services were internal--exclusive to the company network. This
created a screaming need to segment that one humongous and plodding cor-
porate network, connected with sluggish old routers. At first, Cisco just
created faster routers (no doubt about that), but more segmentation was
needed, especially on the Ethernet LANs. The invention of FastEthernet
was a very good and helpful thing too, but it didn't address that network
segmentation need at all.

But devices called bridges did, and they were first used in the network

to break up collision domains. Bridges were sorely limited by the amount
of ports and other network services they could provide, and that's when
layer-2 switches came to the rescue. These switches saved the day by break-
ing up collision domains on each and every port, and switches could provide
hundreds of them! This early, switched LAN looked like the network
pictured in Figure 2.2.

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