Modular Network Design
Top-down network design lets you drill down to the components of the network design, and apply fundamental design principles to the components as well as the overall design.
Hierarchy and redundancy, as mentioned
in the previous sections, are fundamental network design concepts.
Another fundamental concept related to hierarchy is
modularity. Large network design projects and large networks in general consist
of different areas and modules. Each area should be designed using a systematic,
top-down approach, applying hierarchy and redundancy where appropriate. Network
solutions and services can be selected on a per-module basis, but validated as
part of the overall network design.
Cisco Systems uses the Enterprise Composite Network Model
to describe the different components or modules of a typical enterprise network.
The next section briefly describes the model, which is part of Cisco's Secure
Architecture for Enterprises (SAFE).
The Enterprise Composite Network Model
The Enterprise Composite Network Model is a blueprint that
network designers can use to simplify the complexity of a large internetwork.
The blueprint lets you apply a modular, hierarchical approach to network design.
With the Enterprise Composite Network Model, you can analyze the functional,
logical, and physical components of a network, and thus simplify the process of
designing an overall enterprise network.
The Enterprise Composite Network Model comprises three major areas, which can
each be made up of smaller modules:
Enterprise campus. The enterprise campus includes the
modules required to build a robust campus network that provides high
availability, scalability, and flexibility. This area contains all the network
elements for independent operation within one campus location. An enterprise can
have more than one campus.
Enterprise edge. The enterprise edge aggregates the
connectivity from the various elements at the edge of an enterprise network. The
enterprise edge functional area filters traffic from the edge modules and routes
it into the enterprise campus. The enterprise edge contains all the network
elements for efficient and secure communication between the enterprise campus
and remote locations, business partners, mobile users, and the Internet.
Service provider edge. The modules in this functional area
are not implemented by the enterprise. The service provider edge modules are
included to enable communication with other networks using different WAN
technologies and Internet service providers (ISPs).