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Chapter 2
Layer-2 Switching
F I G U R E 2 . 3
The typical switched network design
Switching Services
L
ayer-2 switching is hardware based, which means it uses the MAC
address from the host's NIC cards to filter the network. Unlike bridges that
use software to create and manage a filter table, switches use application-
specific integrated circuits (ASICs) to build and maintain their filter tables.
But it's still okay to think of a layer-2 switch as a multiport bridge because
their basic reason for being is the same: to break up collision domains.
Layer-2 switches and bridges are faster than routers because they don't
take up time looking at the Network layer header information. Instead, they
look at the frame's hardware addresses before deciding to either forward the
frame or drop it.
Layer-2 switching provides the following:
Hardware-based bridging (MAC)
Wire speed
Low latency
Low cost
What makes layer-2 switching so efficient is that no modification to the
data packet takes place. The device only reads the frame encapsulating
the packet, which makes the switching process considerably faster and less
error-prone than routing processes are.
And if you use layer-2 switching for both workgroup connectivity and net-
work segmentation (breaking up collision domains), you can create a flatter
network design with more network segments than you can with traditional
10BaseT shared networks.
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