Basics of MAC Address

MAC Address

Media Access Control is a Physical Address of a System like the IP addresses. They are always represented by decimal value and is a 48 bit value.

A Sample MAC Address looks like: 00-02-A3-B2-67-68

Every piece of hardware on your local network has a MAC address in addition to the IP address assigned to it by the local router, switch or server.

An address system is required to uniquely identify computers and interfaces to allow for local delivery of frames on the Ethernet. Ethernet uses MAC addresses that are 48 bits in length and expressed as 12 hexadecimal digits. The first six hexadecimal digits, which are administered by the IEEE, identify the manufacturer or vendor. This portion of the MAC address is known as the Organizational Unique Identifier (OUI). The remaining six hexadecimal digits represent the interface serial number or another value administered by the manufacturer. MAC addresses are sometimes referred to as burned-in MAC addresses (BIAs) because they are burned into ROM and are copied into RAM when the NIC initializes. 

At the data link layer MAC headers and trailers are added to upper layer data. The header and trailer contain control information intended for the data link layer in the destination system. The data from upper layers is encapsulated within the data link frame, between the header and trailer, and then sent out on the network.

The NIC uses the MAC address to determine if a message should be passed on to the upper layers of the OSI model. The NIC does not use CPU processing time to make this assessment. This enables better communication times on an Ethernet network.

When a device sends data on an Ethernet network, it can use the destination MAC address to open a communication pathway to the other device. The source device attaches a header with the MAC address of the intended destination and sends data through the network. As this data travels along the network media the NIC in each device checks to see if the MAC address matches the physical destination address carried by the data frame. If there is no match, the NIC discards the data frame. When the data reaches the destination node, the NIC makes a copy and passes the frame up the OSI layers. On an Ethernet network, all nodes must examine the MAC header.

All devices that are connected to the Ethernet LAN have MAC addressed interfaces. This includes workstations, printers, routers, and switches.

Network cards each have a unique MAC address. Packets that are sent on the ethernet are always coming from a MAC address and sent to a MAC address. If a network adapter is receiving a packet, it is comparing the packet’s destination MAC address to the adapter’s own MAC address. If the addresses match, the packet is processed, otherwise it is discarded.

MAC Address of any network Card is 6 bytes and 48 bits long. 

Network switches store a list of MAC addresses seen at every port and only forward packets to the ports that need to see the packet.

DHCP servers use the MAC address to identify devices and give some devices fixed IP addresses.

Wanna Check?

Go to command prompt type: 

Start > Run > cmd 

ipconfig/all Enter

 

The network card is responsible for the determining whether the data is intended for it or for another network card. Each network card is given a set of rules that it follows.

 

 -DR