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MAC Address

·449 words·3 mins
lab1918
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lab1918

MAC Address 101
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In Ethernet and other network technologies, a MAC address (Media Access Control address) is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used as a network address for most IEEE 802 network technologies, including Ethernet.

Here are some key points about MAC addresses:

  1. Structure: A MAC address is typically a 48-bit number (6 bytes). It’s often displayed as six pairs of hexadecimal digits, separated by colons or hyphens (e.g., 01:23:45:67:89:AB).

  2. Uniqueness: The MAC address is intended to be globally unique for each device. The first half of the MAC address (the first three octets) identifies the manufacturer of the network interface card (NIC) and is known as the Organizationally Unique Identifier (OUI). The second half is assigned by the manufacturer and should be unique to each device.

  3. Functionality: MAC addresses are used in the data link layer of the OSI model. They help in directing packets of data between devices on the same local network. When data is sent over the Ethernet, the MAC addresses of the sender and receiver are included in each Ethernet frame.

  4. No Routing: MAC addresses operate only within the local network. They are not used for routing data between separate networks; that function is handled by IP addresses in the network layer.

  5. Changes and Spoofing: Although a MAC address is usually fixed to a device, it can be changed or spoofed in software. This can be used for various purposes, including enhancing security or circumventing access controls.

MAC addresses play a crucial role in managing how data is physically transmitted over network cables and helps in ensuring that data packets reach the correct devices.

Common MAC address format
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The common format for representing a MAC address involves six groups of two hexadecimal digits, separated by colons or hyphens. Each hexadecimal digit represents four bits, so two digits (which make up one byte) range from 00 to FF. This results in combinations like the following:

  • Colon-separated format: 01:23:45:67:89:AB
  • Hyphen-separated format: 01-23-45-67-89-AB

Each pair of hexadecimal digits corresponds to one byte, making up a total of six bytes or 48 bits. The MAC address is essentially divided into two parts:

  1. Organizationally Unique Identifier (OUI): The first three bytes of the MAC address identify the manufacturer of the network interface card. This part is assigned by an international body (the IEEE) and ensures that each manufacturer has a unique code.

  2. Device Identifier: The remaining three bytes are assigned by the manufacturer and ensure that each network interface they make has a unique address.

This structure helps in network management, allowing devices to be uniquely identified on a local network level without any ambiguity.