Ethernet: The protocol most widely used to send data across individual links.
Due to sharing collision domain ethernet was invented. Ethernet as a protocol solved this problem by using a technique known as carrier sense multiple access with collision detection.
Carrier sense multiple access with collision detection. (CSMA CD): If there’s no data currently being transmitted on the network segment, a node will fell free to send data. If two or more computer tries to send data at the same time, the computers detect this collision and stop sending data and waits a random interval of time before trying to send data again.
Media access control (MAC) address: globally unique identifier attached to an individual network interface. It is a 48-bit number normally represented by six groupings of two hexadecimal numbers.
Another way to reference each gruop of numbers in a MAC address is an octet. In octet, in computer networking is any number that can be represented by 8-bits.
First three octets of a MAC address are known as the organizationally unique identifier or OUI. These are assigned to individual hardware manufacturers by the IEEE or Institute of Electrical and Electronics Engineers. It can identify the manufacturer of the network interface purely by its MAC address. The last three octets of a MAC address can be assigned in any way that the manufacturer would like with the condition that they only assigned each possible address once to keep all MAC address unique.
How come MAC addresses can be changed when the purpose of MAC address is to keep them unique so the NIC can be identified with its unique MAC address?
MAC spoofing is a technique for changing a factory-assigned MAC addres of a network interface on a networked device.
To change MAC address you can either use the device manager of your OS, use registry edit or a driver program that lets you change the address.
https://www.quora.com/Computer-Hacking-security-Is-it-possible-to-change-MAC-address-If-yes-then-how
Unicast: 1 to 1 transmission, least significant bit in the first octet of a destination address is set to zero = ethernet frame is intended for only the destination address. It would be sent to all devices on the collision domain, but only actually received and processed by the intended destination.
Multicast: If the least significant bit in the first octet of a destination address is set to one, it means you’re dealing with a multicast frame. A multicast frame is similarly set to all devices on the local network segment. What’s different is that it will be accepted or discarded by each device depending on criteria side from their own hardware MAC address.
Broadcast: broadcast is sent to every single device on LAN. This is accomplished by using a special destination known as a broadcast address. Th ethernet broadcast address is all F’s Ethernet broadcasts are used so that devices can learn more about each other.
Data packet: An all-encompassing term that represents any single set of binary data being sent across a network link.
Ethernet frame: Data packets at the Ethernet level, A highly structured collection of information presented in a specific order.