Local Area Network (Lan) Basic Components

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The local area network (LAN) is home to sheer bandwidth and countless client server applications. Different companies have radically different networks; some have a single PC and others have hundreds of locations and thousands of computers. This page is intended to explain the basic principles and components frequently found on the LAN. The internal network is usually built with the highest bandwidth available. It is then connected to a tiny internet connection which is almost always a bottle neck for internet traffic. Most businesses of any size have at least one server to provide extra computing features to the business. The internet is explicitly distrusted and generally the network has protection from the internet built in. The LAN is something that businesses have complete control over. Network devices are much simpler than servers and PCs. It is common (and best practice) to duplicate significant portions of the Network to allow for failure without having a noticeable impact on the network. A LAN is the local cabling and set of network devices at an individual location building or campus but the internal network can easily include many LANs connected to form a WAN.

The internal network, and therefore the LAN, exists to link all of the PCs, laptops, servers, printers, and anything else that might be useful for a computer to talk to. Most LANs have a cable running from every computer to a wall jack. The wall jack is connected to a very similar type of cable that runs to a patch panel in a wiring closet. A patch panel is simply a bank of cable ports that allows all of the cables coming from each wall jack to be connected to the LAN if desired. Any active wall jack must have the corresponding port in the patch panel connected to a switch in the wiring closet. A wiring closet is a centralized room where these cables end. It is common for there to be many wiring closets in a building. The standard is that these wiring closets not actually be used for anything else besides LAN equipment, although this rarely happens in practice. If there are many switches in a wiring closet, they are connected to one or two switches within in the same closet. These serve to connect all of the switches there as well as some of the cable runs entering the room. The switches in a wiring closets are connected to a centralized switch or switch pair in a main wiring closet. The centralized switch or switch pair serves to connect the entire LAN together. These distribution switches connect to the router(s) that the location may have to further connect the switches to the internet or the enterprise WAN thus extending the LAN.

The internet is full of hackers which means that the traffic that comes from the internet is usually distrusted. On most local area networks there are more things that communicate or are set up to communicate than are used and fewer that are really needed. However everything that is on a computer that communicates on the LAN is a potential vulnerability for a hacker to exploit. For this reason most networks use a firewall which simply restricts what can communicate (IP address) to what is on the other side of a firewall and what type of communications (port number) can pass through it. Generally this means that only the things frequently used are allowed to pass through it. The idea is that anything that is not a business need is not allowed through which greatly reduces what a hacker can attack. In reality it does leave many options open for attack, although it is certainly a much smaller set of options than what would be available without it. Because the servers that communicate directly with the internet are considered the highest risk these are frequently placed in what’s called a demilitarized zone (DMZ). This simply means that the traffic to and from these servers and the normal internal network is restricted by additional firewalls. Some DMZ’s have additional firewalls inside them to further protect the LAN from...
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