Search:

CISA - Physical Network Design

The first computer networks were created by connecting serial ports between two computers.

This primitive design used modem software to handle file transfer between systems. Networks evolved with the invention of token passing and broadcast transmissions. The invention of the hub, or shared media access unit, created the opportunity to connect multiple computers together on the same segment (referred to as a subnet).

The concept of a network bridge was created to connect two subnets into the same, single subnet. A layer 2 bridge allows all traffic to pass from one side to the next. The bridge could be configured to allow broadcast across it or configured to filter broadcasts and reduce noise—it depended on the bridge manufacturer’s design.

Later, it became apparent that it would be necessary to connect two separate networks
together without merging them into a single subnet as a bridge would. Many people complained
that too many systems were creating too much traffic when all the computers were
located within one giant subnet.

Thus came the development of a router. Early routers were simply a computer with two interface
cards. Interface 1 serviced a connection to LAN 1, and interface 2 provided a connection to
LAN 2. A software-routing program was then loaded to be run on the computer’s CPU.
The routing program basically determines whether individual traffic requests need to cross
to the other side.

If so, the router passes the request through the other LAN interface to reach its destination. If the destination is within the same subnet (LAN 1 to LAN 1), the router will not pass the traffic. This protects the other subnet from unnecessary data transmission noise (LAN 2). That is the basic function of a router. Routers forward data traffic when necessary and insulate users on other subnets.

In modern networks, the routing function can be loaded onto a router card installed
in the network switch chassis. Traditional routers are usually a dedicated device in their
own chassis.