56
Chapter 1
Internetworking
functions to be included at the access layer:
Continued (from distribution layer) access control and policies
Creation of separate collision domains (segmentation)
Workgroup connectivity into the distribution layer
Technologies such as DDR and Ethernet switching are frequently seen in
the access layer. Static routing (instead of dynamic routing protocols) is seen
here as well.
As already noted, three separate levels does not imply three separate routers.
There could be fewer, or there could be more. Remember, this is a layered
approach.
Summary
P
hew! I know that seemed like the chapter that wouldn't end, but it
did--and you made it! You're now armed with a ton of fundamental infor-
mation; you're ready to build upon it, and well on your way to certification.
This chapter began with a discussion of the OSI model--the seven-layer
model used to help application developers design applications that can run
on any type of system or network. Each layer has its special jobs and select
responsibilities within the model to ensure that solid, effective communica-
tions do, in fact, occur. I provided you with complete details of each layer
and discussed how Cisco views the specifications of the OSI model.
In addition, each layer in the OSI model specifies different types of devices.
I described the different types of devices, cables, and connectors used at each
layer. Remember that hubs are Physical layer devices and repeat the digital sig-
nal to all segments except the one it was received from. Switches segment the
network using hardware addresses and break up collision domains. Routers
break up broadcast domains and use logical addressing to send packets through
an internetwork.
Cisco makes a large range of router, hub, and switch products. I discussed
the different products Cisco creates and sells so that you can make more
informed decisions when building and buying for your internetwork.
Lastly, this chapter covered the Cisco three-layer hierarchical model. I
described in detail the three layers and how each is used to help design and
implement a Cisco internetwork.
Copyright ©2002 SYBEX, Inc., Alameda, CA
www.sybex.com