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Before Layer-2 Switching

et's go back in time a bit and take a look at the condition of net-

works before switches and how switches have helped segment the corporate
LAN. Before LAN switching, the typical network design looked like the
network in Figure 2.1.

F I G U R E 2 . 1

Before switching

The design in Figure 2.1 was called a collapsed backbone because all hosts

would need to go to the corporate backbone to reach any network services--
both LAN and mainframe.

Going back even further, before networks like the one shown in Figure 2.1

had physical segmentation devices like routers and hubs, there was the main-
frame network. This network included the mainframe (IBM, Honeywell,
Sperry, DEC, etc.), controllers, and dumb terminals that connected into the
controller. Any remote sites were connected to the mainframe with bridges.

And then the PC began its rise to stardom, and the mainframe was con-

nected to the Ethernet or to a Token Ring LAN where the servers were
installed. These servers were usually O/S 2 or LAN Manager because this
was "pre-NT." Each floor of a building ran either coax or twisted-pair

Corporate

Remote Branch

Server Farm

Token Ring

Hubs

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