After the requirements for the overall
network have been gathered, an overall topology or model of the LAN
can be developed.
The major
pieces of this topology design can be broken into three unique
categories of the OSI model. 
Layer 1 - Physical Layer
Includes wire media type such as CAT5
UTP and fiber-optic cable along with TIA/EIA-568-A Standard for layout
and connection of wiring schemes.
Design Goal
- Build this layer of the OSI model
with speed and expansion capabilities.
Layer 2 - Data Link Layer
Includes selection of Layer 2 devices
such as bridges or LAN switches used to interconnect the Layer 1
media to a LAN segment. Devices at this layer will determine the
size of the collision and broadcast domains.
Design Goals
- Create a concentration point within
the MDFs or IDFs where end hosts can be grouped at Layer 1 to form
a physical LAN segment.
- Install LAN switching devices that
use microsegmentation in order to reduce the collision domain
size.
- Create a point (at Layer 2) of the
topology where users can be grouped into virtual workgroups (VLANs)
and unique broadcast domains.
Layer 3 - Network Layer
Includes selection of Layer 3 devices
such as routers that are used to create unique LAN segments and
allow communication between segments based on Layer 3 addressing
such as IP addressing.
Design Goals
- Build a path between LAN segments
that will filter the flow of data packets.
- Isolate ARP broadcasts.
- Isolation of collisions between
segments.
- Filtering of Layer 4 services
between segments.
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