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The switch floods the frame with the hope that the unknown device will be on some other Ethernet segment, it will reply, and the switch will build a correct entry in the address table.
#Mac address flooding definition mac
Switches forward unknown unicast frames, which are frames whose destination MAC addresses are not yet in the bridging table, out all ports as well. So the switch simply forwards broadcasts out all ports, except the one on which the broadcast was received. LAN broadcasts, by definition, are received by all devices on the same LAN. This is more common when using main frame systems that communicate via MAC addresses rather than protocol addresses (such as IP addresses).īridges forward LAN broadcast frames, and unknown unicast frames, out all ports. This is a technique used by hackers to circumvent MAC-based security restrictions. Typically, the problem of duplicate MAC addresses arises because people choose not to use the vendor-assigned hardware address, but instead use a self-assigned address (also called a locally administered address).
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This address is assigned by the hardware manufacturer and is globally unique, so you should not have duplicate addresses on your network (although cards with duplicate addresses have been manufactured by production errors in the past). The MAC address is a 12-digit hexadecimal number or 48 bits in length. The MAC address is taken by default from the hardware address of the network card. The MAC address is placed in the table, along with the interface in which the frame arrived. If a frame enters the switch, and the source MAC address is not in the address table, the switch creates an entry in the table. Switches build the MAC address table by listening to incoming frames and examining the frame's source MAC address.
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With a full, accurate MAC address table, the switch can make accurate forwarding and filtering decisions. Switches dynamically learn the MAC addresses in the network to build its MAC address table. The filter-versus-forward decision works best when the switch knows where all the MAC addresses are in the network.