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

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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2 Answers 2


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.


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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