Summary
35
Eliminate Peering Problems
Because routing is typically performed in the distribution layer devices, each
distribution layer device must have reachability information about each of
the other distribution layer devices. These layer 3 devices use routing proto-
cols to maintain the state and reachability information about neighbor rout-
ers. This means that each distribution device becomes a peer with every other
distribution layer device, and scalability becomes an issue because every
device has to keep information for every other device.
If your layer 3 devices are located in the core, you can create a hierarchy,
and the distribution layer devices will no longer be peer to each other's dis-
tribution device. This is typical in an environment in which there are more
than 100 switch blocks.
Summary
I
n this chapter, you learned about switches and the different models
available from Cisco. It is imperative that you understand the different mod-
els and what they are used for in the Cisco hierarchical design.
The past and future requirements of campus internetworks are an impor-
tant part of your studies for your Cisco Switching exam. We discussed the
current campus designs as well as how to implement FastEthernet, Gigabit
Ethernet, Fast EtherChannel, and Multi-Layer Switching (MLS) in the
emerging campus designs.
We also discussed the differences between layer 2, layer 3, and layer 4
switching technologies. You learned about the Cisco three-layer model and
the different catalyst switches that can be implemented at each layer of the
Cisco model.
The chapter ended with a discussion of the switch and core blocks, which
are based on the Cisco three-layer model, and how to design networks based
on this model.
Copyright ©2000 SYBEX , Inc., Alameda, CA
www.sybex.com