20
Chapter 1
The Campus Network
combination of high-speed scalability with low latency by using huge filter
tables based on the criteria designed by the network administrator.
Multi-layer switching can move traffic at wire speed and also provide
layer 3 routing, which can remove the bottleneck from the network routers.
This technology is based on the idea of route once, switch many.
Multi-layer switching can make routing/switching decisions based on the
following:
MAC source/destination address in a Data Link frame
IP source/destination address in the Network layer header
Protocol filed in the Network layer header
Port source/destination numbers in the Transport layer header
There is no performance difference between a layer 3 and a layer 4 switch
because the routing/switching is all hardware based.
MLS will be discussed in more detail in Chapter 8.
It is important that you have an understanding of the different OSI layers
and what they provide before continuing on to the Cisco three-layer hierar-
chical model.
The Cisco Hierarchical Model
M
ost of us learned about hierarchy early in life. Anyone with older
siblings learned what it was like to be at the bottom of the hierarchy! Regard-
less of where you were first exposed to hierarchy, most of us experience it in
many aspects of our lives. Hierarchy helps us to understand where things
belong, how things fit together, and what functions go where. It brings order
and understandability to otherwise complex models. If you want a pay raise,
hierarchy dictates that you ask your boss, not your subordinate. That is the
person whose role it is to grant (or deny) your request.
Hierarchy has many of the same benefits in network design that it has in
other areas. When used properly in network design, it makes networks more
predictable. It helps us to define and expect at which levels of the hierarchy
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