LAN Switches, The Local Area Network: Basics, MAC address

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What are LAN Switches

A LAN switch is a local area networking device that prevents data packet collision, and maximizes transmission speed as well as bandwidth allocation. This is a good replacement to a network hub and solves problems associated with expanding networks.

The LAN Switch Mechanism and Its Advantages

In a network where a LAN switch is used, each node gets a direct connection to a switch. That is, a node gets a dedicated connection to the switch which only it (the node or the computer) and the switch use. This dedicated connection makes it possible for one node to maximize use of the bandwidth available to it. After all, no other node is competing with it for bandwidth. This means speedy data transmission.

Moreover, the connection between the node and the switch can be made using cabling which has a separate route for data that the node is sending out and a separate route for data that the switch is forwarding to the node. This eliminates problems of data collision.

The LAN switch is especially a vast improvement over the network hub since it has the ability to “read” the source and destination node of a data packet and forward the packet only to the destination node.

Whenever the node transmits data meant for another node in the local area network, the switch intercepts the data, determines the destination and forwards the transmission to its intended destination. Since a data packet does not get broadcasted to unnecessary segments, network congestion is minimized and network bandwidth is conserved.

The Local Area Network: Basics

LAN, as you know, is the geographically limited network; it is usually limited to a single office, home, department, or building. In some cases, though, a LAN can exist between neighboring buildings.

It is comprised of various nodes – these are usually desktop computers and computer servers – that are physically connected through LAN cables or through a wireless router and are able to communicate with each other and share common resources (e.g. office printers).

There are many ways of connecting the various nodes in a Local Area Network. Simple networks usually have nodes that are arranged in a bus (straight backbone with segments where nodes are attached) or ring topology (nodes are distributed on a circular backbone and only the node with the ring token can transmit or send data).

They can also be arranged in a star-like arrangement where all nodes have an individual segment connecting them to a hub. The hub is a passive network device; it is simply a place where data packets pass from one node to all the other nodes connected to it (except the port from which the data originally came from). Complex networks are usually a combination of the bus and star typology. Backbones connect multiple hubs.

All these networks have different physical properties (they vary in the way a node can send and receive data to another node), but all these suffer from inefficient bandwidth usage, extremely low speeds and data collision incidence.

What is a MAC address

A MAC address is an address which exists on Layer 2 of the OSI Model.

Layer 2 of the OSI model is the Data Link Layer. The Data Link Layer consists of two sublayers, the Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sublayer controls how a network node gains access to the data and permission to transmit it.

MAC addresses are globally unique addressed that are written into hardware at the time of manufacture. For this reason, MAC addresses are sometimes called Burned In Addresses (BIA).

After manufacture, it is possible in many cases to change the MAC address of a device in software.

MAC addresses are used by many different Layer 2 technologies, including Ethernet, Token Ring, 802.11, Bluetooth, FDDI, ATM, SCSI, and Fibre Channel.

Because MAC addresses originated in the Ethernet specification, the MAC address is sometimes referred to as the Ethernet Address.

A MAC address is 48 bits long. This means that there are 281,474,976,710,656 possible MAC addresses.

A sample MAC address looks like this:

00-0C-F1-56-98-AD

The first three bytes of this address (00-0C-F1) identify the manufacture of this network device, in this case Intel.

These first three bytes are assigned by the IEEE and the database is available online at IEEE OUI and Company_id Assignments.

The last three bytes of this address were assigned by Intel when they device was manufactured.

How do I Change a MAC address

Every Ethernet card has a MAC address burned-in at the factory. At times, you may want to change this MAC address to one of your own choosing.

The procedures to change a MAC address are specific to each operating system.

How to change a MAC address in Microsoft Windows

Under Windows, the MAC address is stored in a registry key. To change a MAC address, find that key with `regedit` and change it. Of course, Microsoft keeps moving the location of the key around!

Windows XP adds an option to change the MAC address on some network cards under the Advanced tab in the network adapter's Properties menu.

A much easier and more reliable method to change a MAC address under Windows is to use a software utility program designed to do this for you.

Macshift is a free utility that you can use to spoof your MAC address under Microsoft Windows.