From the course: CISSP Cert Prep (2021): 4 Communication and Network Security

Routers, switches, and bridges

From the course: CISSP Cert Prep (2021): 4 Communication and Network Security

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Routers, switches, and bridges

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- [Instructor] Networks carry all types of data over distances short and far. Whether it's a transatlantic video conference or an email across the room, many different networks carry the ones and zeros that make communications work. Routers, switches, and bridges are the core building blocks of these networks. Network engineers use switches to connect devices to networks. Switches are simple-looking devices, such as the one shown here, that contain a large number of network ports. Switches may be very small with eight or fewer ports, or they can be quite large with 500 or more ports. The switch shown here is a 96-port switch. Switches are normally hidden away inside wiring closets and other secure locations. Each switch port is connected to one end of a network cable. Those cables then disappear into special pipes known as conduits for distribution around a building. When the cable reaches the final destination, it usually terminates in a neat-looking wall faceplate like the one shown here. This provides an easy way for users and technicians to connect and disconnect computers from the network without damaging the cables inside the wall or having unsightly, unused wires lying around the room. Some devices connect to switch ports through the use of wired networks. Many other devices don't use wires but instead depend upon radio-based wireless networks. These networks are created by wireless access points like the one shown here. These APs, as they're called, contain radios that send and receive network signals to mobile devices. The AP itself has a wired connection back to the switch, allowing the wireless devices to connect to the rest of the network. Switches do create networks, but they're limited to creating local networks. Switches operate at layer two of the OSI model, the data link layer, where they work with MAC addresses only. Some switches also have the capability of working at layer three of the OSI model, the network layer, where they can interpret IP addresses. In those cases, switches are beginning to take on the function of routers. Routers play a higher-level role, connecting networks together by serving as a central aggregation point for network traffic heading to or from a large network. The router serves as the air traffic controller of the network, making decisions about the best paths for traffic to follow as it travels to its final destination. Routers also perform some security functions, using access control lists to limit the traffic that may enter or leave a network based upon the organization's security policies. This type of filtering using access control lists does not pay attention to connection state and it's known as stateless inspection. In the next video, you'll learn how firewalls extend this capability with stateful inspection. Bridges, like switches, are layer two devices, but they perform a very limited function. Bridges just connect two networks together. They learn the MAC addresses present on each network and then forward traffic between the networks when appropriate.

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