16
Chapter 1
The Campus Network
(ASICs) to build and maintain filter tables. It is OK to think of a layer 2
switch as a multiport bridge.
Layer 2 switching provides the following:
Hardware-based bridging (MAC)
Wire speed
High speed
Low latency
Low cost
Layer 2 switching is so efficient because there is no modification to the
data packet, only to the frame encapsulation of the packet, and only when
the data packet is passing through dissimilar media (such as from Ethernet
to FDDI).
Use layer 2 switching for workgroup connectivity and network segmen-
tation (breaking up collision domains). This allows you to create a flatter
network design and one with more network segments than traditional
10BaseT shared networks.
Layer 2 switching has helped develop new components in the network
infrastructure:
Server farms Servers are no longer distributed to physical locations
because virtual LANs can be created to create broadcast domains in a
switched internetwork. This means that all servers can be placed in a cen-
tral location, yet a certain server can still be part of a workgroup in a
remote branch, for example.
Intranets Allows organization-wide client/server communications based
on a Web technology.
These new technologies are allowing more data to flow off of local sub-
nets and onto a routed network, where a router's performance can become
the bottleneck.
Limitations of Layer 2 Switching
Layer 2 switches have the same limitations as bridge networks. Remember
that bridges are good if you design the network by the 80/20 rule: users
spend 80 percent of their time on their local segment.
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