If you were assigned an OUI of 01:23:45, the network equipment you manufactured would typically be numbered from 01:23:45:00:00:01 through 01:23:45:FF:FF:FE and you could be reasonably certain that other manufacturers would not use your numbers.
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Each manufacturer of networking equipment was assigned an OUI, and was free to assign their own numbers in that block.
The first three bytes of a MAC address were originally known as OUI’s, or Organizational Unique Identifiers. Dividing up the MAC addresses, has made it easier for creators of networking equipment to each own a “block” of addresses that they can pick address numbers from. In order to keep track of addresses, and establish some order, addresses are broken up into “chunks,” somewhat like area-codes. Like phone numbers, there are supposed to be no duplicate addresses within the same network. In order to make these addresses easier for humans to remember, these addresses are usually written as six two-digit hexadecimal numbers, such as 01:23:45:67:89:AB. MAC Addresses are 6 bytes (or 48 bits long), providing 281,474,976,710,656 addresses in theory. This enables LAN equipment to more quickly sort network traffic and determine whether a network frame needs attention from them. (See the 3 rd and 4 th fields.) In order to speed up LAN equipment, the Destination address and Source (Sender) address are sent in the very first parts of a frame. You can see the MAC Destination and MAC Source addresses in the typical Ethernet Frame shown in Figure 1. Let’s take a look at a typical Ethernet Frame: MAC Addresses are used in Ethernet, WiFi, Bluetooth, and a number of other network types. The same type of LAN address scheme is used to identify the senders of these Frames so that replies can be sent.The addresses used in an Ethernet network are known as MAC (Media Access Control) addresses.
Like packages or envelopes passing through post offices, these frames need to be labeled with an address, which enables anything handling that frame to know where to send the LAN frame and to whom the LAN frame is being sent. Addresses: Where Do You Want To Go?Īll information sent on an Ethernet LAN network is broken up into “Frames” for easy transport. (To be fair, it was cold out and nearly lunchtime!) “Go ahead and slip some lunch into the microwave oven and while we’re waiting for it to heat up, I’ll try to explain things,” I said with as much patience as I could muster. Trying to find out what he already knew, I asked, “What do you think a MAC address might be?” The answer I got was: “The mailing address of the warehouse where they make Mac & Cheese?” (sigh) I see my work is cut out for me. I was recently asked by one of the managers at an organization to explain what a MAC Address was and what role it plays in the network. Not the address of the US Federal Cheese Repository…