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To get a large number of PCs connected, specialist equipment has been designed to carry out certain tasks such as preventing broadcast storms and keeping track of which networks are where.
These are pretty self-explanatory. PCs and servers are the devices requesting and providing network services. Servers provide authentication for users logging onto the network, internet access, firewall services and many other functions.
Often referred to NIC (network interface card), these are used with PCs, Servers and printers to allow communication on the network take place. Every single NIC has an address burned onto a chip that sits on the card. This address is known as a hardware or MAC address.
Fig 1.1 PCI Network Card
The most basic piece of networking equipment is a hub. A hub simply allows several networking devices to speak to each other. Each device plugs into a port on the hub. The simplest network you can build will be with some PCs connecting into a hub. Hubs have no memory or hard drive so they can never remember which device is plugged into which port. This causes a lot of unnecessary traffic to pass on the network.
FIG 1.2 HP 16 Port Hub
A drawback of using hubs is that a hub can never keep a record of which PC is plugged into which port. For this reason, every time one PC wants to speak to another, every single PC plugged into the hub gets the message as well. This is known as a broadcast.
Switches build up a list of which PCs are connected to which ports allowing the available bandwidth to be used a lot more efficiently. If a PC wants to speak to another PC that is not directly connected to it, the switch will send out a broadcast to find out where on the network the PC actually is. Switches and hubs are designed to forward broadcast traffic.
FIG 1.3 Cisco 24 port switch
A router can be considered to be a large directory of networks. Rather than concerning itself about which PC is where, a routers job is to find out where different networks are. It then sends the traffic via the best path, be it the fastest, most reliable or shortest. If the router does not know how to get to its intended destination it will either drop the packet or forward it to another router who should know how to get there.
It is important to remember that by default, routers do not forward broadcasts. If they did we would find that most networks including the internet would be extremely slow because of all the broadcasts passing across them.
FIG 1.4 Cisco 2503 router