The MAC address used by the spanning tree algorithm (STA) implemented in a given switch does not belong to any of its Ethernet interfaces. At least in Cisco implementations, this MAC address is known as base MAC or universal (burned-in) MAC and its purpose is to identify the switch itself, not some of its Ethernet interfaces. For this reason, this MAC address is printed on a label attached on the back of the device.
You can check a device's base MAC by issuing the show version command:
SW1#show version Cisco IOS Software, C2960 Software (C2960-LANBASE-M),
Version 12.2(25)FX, RELEASE SOFTWARE (fc1) Copyright (c) 1986-2005 by
Cisco Systems, Inc. Compiled Wed 12-Oct-05 22:05 by pt_team
ROM: C2960 Boot Loader (C2960-HBOOT-M) Version 12.2(25r)FX, RELEASE
System returned to ROM by power-on
Cisco WS-C2960-24TT (RC32300) processor (revision C0) with 21039K
bytes of memory.
24 FastEthernet/IEEE 802.3 interface(s) 2 Gigabit Ethernet/IEEE 802.3
63488K bytes of flash-simulated non-volatile configuration memory.
Base ethernet MAC Address : 0001.43BA.DE15
Motherboard assembly number : 73-9832-06 Power supply part number :
341-0097-02 Motherboard serial number : FOC103248MJ Power supply
serial number : DCA102133JA Model revision number : B0
Motherboard revision number : C0 Model number :
WS-C2960-24TT System serial number : FOC1033Z1EY Top
Assembly Part Number : 800-26671-02 Top Assembly Revision
Number : B0 Version ID : V02
CLEI Code Number : COM3K00BRA
Hardware Board Revision Number : 0x01
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