You might find a particular vendor having more than just one code this is because of the wide range of products they might have. The Vendor code is specified by RFC - 1700. To avoid these kind of problems, the IEEE group split the MAC address in half, and used the first half to identify the vendor, and the second half is for the vendor to allocate as serial numbers: When a vendor, e.g Intel, produces network cards for computers, they don't just assign them any MAC address they like, this would create a big confusion in identifying who is the vendor of each network card and could possibly result in clashing with another MAC address from another vendor e.g D-link, who happened to choose the same MAC address for their network card! It is very rare that a MAC address is represented in Binary format because it is simply too long and difficult to understand, as we will see futher on. MAC Addresses are always presented in HEX format, just as our example above. Let's now have a look at a MAC address and see what it looks like! We will use our workstation's MAC address as an example: If the packet is destined for the computer then the MAC address in the destination field of the packet will match, so it will accept it and pass it onto the Layer above (3) which, in turn, will check the network address of the packet (IP Address), to make sure it matches with the network address to which the computer has been configured. The Physical Layer understands the electrical signals on the network and creates the frame which gets passed to the Datalink layer. All machines on a network will listen for packets that have their MAC address in the destination field of the packet (they also listen for broadcasts and other stuff, but that's analysed in other sections). This is where the MAC address - Layer 2 comes into the picture. You see, the IP address of a machine exists on the 3rd Layer of the OSI model and, when a packet reaches the computer, it will travel from Layer 1 upwards, so we need to be able to identify the computer before Layer 3. The diagram below provides a visual representation how important MAC Addresses are on our network and at which layer of the OSI Model they exist: If you're thinking of IP addresses, then you're correct to some extent, because an IP address does identify one unique machine on a network, but that is not enough. The Reason for MACĮach computer on a network needs to be identified in some way. The reason for this is that the MAC address is actually "burnt-in" into your network card's memory chipset. Logical addresses require you to load special drivers and protocols in order to be able to configure your network card/computer with an IP Address, whereas a MAC address doesn't require any drivers whatsoever. MAC addresses are physical addresses, unlike IP addresses which are logical addresses. We are going to analyse them in depth here so we can get a firm understanding of them since they are part of the fundamentals of networking. Media Access Control (MAC) addresses are talked about in various sections on the site, such as the OSI-Layer 2, Multicast, Broadcast and Unicast.
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