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I am working with Cisco Nexus 3000 switch. I was under the assumption that a switch will always have a single MAC address but when I ran the following command, it displayed two different MAC addresses though only the first two bytes were different.

show interface ethernet 1/17 mac-address

Output:
MAC-Address              Burn-in-Mac-Address
ab:cd:ef:gh:ij:12        ab:cd:ef:gh:ij:78

Each interface on the switch has a different MAC. Can someone explain to me the importance of this? When does the common MAC address and interface specific addresses be used?

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  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Aug 7 '17 at 22:40
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Cisco assigns a large block, e.g. 1024, MAC addresses to a switch supervisor for use in STP because Cisco defaults to PVST+ and needs a MAC address for each VLAN. Each interface that may send ethernet traffic needs a unique MAC address. Logical interfaces, e.g. SVIs, will also get MAC addresses.

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If we are having 24 port switch then each port is equipped with mac -address .

Mac -address is layer2 contruct . To forward packet from layer3 to layer1. Layer2 acts as mediator hence frame is forwarded from layer2 to layer1 and layer2 to layer3 on basis of mac-address table .

Mac -address table maps

Mac-address to switch ports

Switch(config)#show mac address-table Mac Address Table


Vlan Mac Address Type Ports


  1. 00ld.70ab.5d60 DYNAMIC Fa0/2

  2. 00le.f724.al60 DYNAMIC Fa0/3

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