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Lesson 5 Switches, bridges, and routers
Objective Describe the functions of switches, bridges, and routers.

What are switches, bridges, and routers?

Switches, bridges, and routers are products that interconnect LANs, WANs, and networks of different types. They orchestrate the entire networking system, and therefore are critically important to the overall performance of your solution. Switches, bridges, and routers all interconnect the networks that will make up your solution, so it's important to understand the differences among them.

Switches

A switch is a network device that filters and forwards data packets between LAN segments. In so doing, they compensate for speed differences between networks. Switches operate at the data link layer (layer 2) of the OSI Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs.[1] This graphic illustrates a switch.


This diagram illustrates a switch between two local area networks.

Bridges

A bridge is a device that connects two LANs or two segments of the same LAN. Like switches, they too compensate for network speed differences.
With bridges, the two LANs being connected can be similar or dissimilar. Like switches, bridges operate at the data link layer (layer 2) of the OSI Reference Model and therefore are protocol-independent. They simply forward data packets without analyzing and re-routing messages. This graphic illustrates a bridges.

A network bridge is a computer networking device that creates a single aggregate network from multiple communication networks or network segments.

Routers


A router is a device that connects any number of LANs, as shown here.
A router is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions on the Internet.

Routers use headers and a forwarding table to determine where packets should go. In addition, in contrast to bridges, they also use specific routing protocols to communicate with each other and configure the best route between any two hosts.
In general, routers perform very little data filtering and they do not care about the type of data they handle. The table below clarifies the defining characteristics of switches, bridges, and routers.

Characteristic Switches Bridges Routers
How they process information Filter, forward, and convert packet information Filter, forward, and convert packet information Forward packet information and perform address directory mapping and resolution.
Their benefit to networking Compensate for speed differences between different networks Compensate for speed differences between different networks Balance and filter traffic within LAN groups for security purposes and policy mangement
Where they are based Hardware Software Hardware
Where they work Data-link layer (OSI 2 layer) Data-link layer (OSI 2 layer) Networking layer (OSI layer 3)
[1]Switched LANs: LANs that use switches to join segments.