comptia Network+ : Network Devices (hub, Repeater, Bridge, Switch, Router, Gateways And Brouter)

2. Infrastructure

2.2 Placement of networking devices on a network and install/configure them

Switch: Switches work at layer 2 of OSI model, which is Data Link Layer. A switch looks at the destination MAC address before forwarding a frame. It may be noted that there are some layer 3 switches. Though these devices are called switches, they typically do the routing. When we say switches, we mean layer 2 switches (or simple switches). A switch uses OSI layer 2 address (MAC Addresses) for forwarding frames. A switch can be used to reduce network traffic by dividing the broadcast domains of a network. Switches are the connectivity points of an Ethernet network. Devices connect to switches via twisted-pair cabling, one cable for each device

The main function of a content switch is to inspect the network data that it receives so that it can decide where on the network that data (or request) needs to be forwarded to.

Router: The following are true about routers:

• Routers work at the network layer of ISO-OSI model and responsible for forwarding packets based on logical address.
• Routers do not forward broadcasts. Note that typically, switches and hubs forward broadcasts.
• Routers are required when you have more than one subnet in your network.

Hub: Hubs are simple devices that direct data packets to all devices connected to the hub, regardless of whether the data packet is destined for the device. This makes them inefficient devices and can create a performance bottleneck on busy networks.

The difference between hubs and switches is in how the devices deal with the data they receive. Whereas a hub forwards the data it receives to all the ports on the device, a switch forwards it to only the port that connects to the destination device. It does this by the MAC address of the devices attached to it and then by matching the destination MAC address in the data it receives.

Hubs and switches have two types of ports:

• Medium Dependent Interface (MDI) and
• Medium Dependent Interface Crossed (MDI-X).

The two types of ports differ in their wiring. As the X implies, an MDI-X port’s wiring is crossed; this is because the transmit wire from the connected device must be wired to the receive line on the other. Rather than use a crossover cable, you can use the more simple straight-through cable to connect systems to the switch or hub.

Three different types of hubs are widely known. These are:

• Passive hub
• Active hub
• Intelligent hub

Passive hubs do not amplify the electrical signal of incoming packets before broadcasting them out to the network.

Active hubs, on the other hand, amplify the received signal before sending them out. Some people use the terms concentrator when referring to a passive hub and multiport repeater when referring to an active hub.

An intelligent (also called smart) hub typically is stackable (built in such a way that multiple units can be placed one on top of the other to conserve space). It also typically includes remote management capabilities via SNMP and virtual LAN (VLAN) support.

A network hub operates at the physical layer of the OSI model. A router operates at the network layer of the OSI model. A Wireless bridge operates at the data link layer of the osi model. A NIC and Access Point operates at the data link layer of the osi model. There are two main types of switches. Layer-2 switches operate at the data-link layer of the OSI model and are based on bridging technologies. They establish logical connections between ports based on MAC addresses. Layer-3 switches operate at the layer 3(network layer) of the OSI model and are based on routing technologies. They establish logical connections between ports based on network addresses. Layer-3 switches are sometimes called routing switches or multilayer switches.