MAC - changing the MAC address on a switchport

It is possible to use the mac-address command on a Cisco switch to change the MAC address used by that interface. It can be done something like this:

SW(config-if)#mac-address AAAA.AAAA.AAAA

If you then take a look at the output of the show interface command, you will see the following:

SW(config-if)#exit
SW(config)#exit
SW#show interfaces gig 0/0
GigabitEthernet0/0 is up, line protocol is up (connected)
  Hardware is iGbE, address is aaaa.aaaa.aaaa (bia 5254.0000.49a8)
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
!<---- Output Omitted ---->

You can see that the hardware address has been changed to aaaa.aaaa.aaaa, however, the BIA, which is the Burned In Address remains the original value of 5254.0000.49a8.

It is important to note that even if you change the MAC address of a switchport, protocols that may use the MAC address for their operation will still use the BIA address. For example, Spanning Tree Protocol (STP), LACP, CDP, DTP, VTP, VRRP, and others will all still use the BIA address.