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Chapter 1
Scaling Large Internetworks
Things to avoid at the Distribution layer are limited to those functions
that exclusively belong to one of the other layers.
The Access Layer
The Access layer controls user and workgroup access to internetwork
resources. The Access layer is sometimes referred to as the desktop layer. The
network resources that most users need will be available locally. The Distri-
bution layer handles any traffic for remote services. The functions to be
included at this layer include
Continued (from the 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 as well as the Distribution layer. If you are using DDR to
connect to a remote office, then it has to be a Distribution layer device. Static
routing (instead of dynamic routing protocols) is seen here as well.
As already noted, three separate levels does not have to imply three sep-
arate routers. It could be fewer, or it could be more. Remember, this is a lay-
Requirements of the Scalable Internetwork
oday's internetworks are experiencing extraordinary growth due to
increasing demands for connectivity both in businesses and at home. There-
fore, it's very important for them to be scalable. It's now vital for adminis-
trators to understand what a scalable network is, as well as what is required
to effectively manage its incessant growth.
Since a scalable internetwork undergoes continual growth, it must be
both flexible and easily appended. An ideal design is based on the hierarchi-
cal model to simplify management and permit well-planned growth that
honors the network's requirements. Here are the requirements of a scalable
It must be reliable and available. The Cisco IOS provides features for
implementing redundancy, load balancing, and reachability with proto-
cols such as OSPF and EIGRP.
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