Thanks again to everyone for responding...I understand the mechanics of STP...I am confused on the use of MAC addresses on switches. I have cut and pasted from some Cisco documentation and perhaps that will help identify where my confusion is originating.
MAC Addresses on Layer 2 Interfaces
MAC addresses of Layer 2 Interfaces (Switchports) are unique and are assigned to that particular line module. In Cisco 6500/6000, 4500/4000, 3750, 3560, 3550, and 2970 series switches, you are not able to change the MAC address on a switchport. In Cisco 2940, and 2950/2955 series switches you can change the MAC address of switch ports using the command mac-address, under the interface configuration mode.
MAC Addresses for Spanning Tree Computation
MAC addresses used for Spanning Tree calculations are stored in an EEPROM present in the Supervisor module. Regardless of the types of line modules installed, the Layer 2 MAC addresses for VLANs do not change unless you replace the Supervisor module. If you do replace the Supervisor module, the Layer 2 MAC addresses of all VLANs change to those specified in the address allocator on the new Supervisor module. In the fixed configuration Catalyst switches, MAC addresses for VLANs cannot be changed.
Catalyst Switch with Support for CLI Configuration of a Unique MAC Address per Interface
This section discusses switches that support a change in MAC addresses per interface.
Catalyst 6500/6000 Supervisor Engine 720 and Supervisor Engine I with MSFC1, MSFC2, or MSFC3 That Runs CatOS System Software
This output is from the MSFC1 in which the default MAC address is the same for all interfaces:
cs-6506-24a#show interfaces | include line | address
Vlan1 is down, line protocol is down
Hardware is Cat6k RP Virtual Ethernet, address is 00d0.bcf1.ee5c (bia 00d0.bcf1.ee5c)
Internet address is 14.18.2.182/16
Vlan2 is down, line protocol is down
Hardware is Cat6k RP Virtual Ethernet, address is 00d0.bcf1.ee5c (bia 00d0.bcf1.ee5c)
cs-6506-24a#Use the mac-address mac_address interface configuration command in order to change the MAC address. Here is an example:
cs-6506-24a#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
cs-6506-24a(config)#interface vlan 1
cs-6506-24a(config-if)#mac-address 0007.0001.0001
cs-6506-24a(config-if)#exit
cs-6506-24a(config)#interface vlan 2
cs-6506-24a(config-if)#mac-address 0007.0001.0002
cs-6506-24a(config-if)#end
cs-6506-24a#Verify the change in the MAC address in this way:
cs-6506-24a#show interfaces | include line | address
Vlan1 is down, line protocol is down
Hardware is Cat6k RP Virtual Ethernet, address is 0007.0001.0001 (bia 00d0.bcf1.ee5c)
Internet address is 14.18.2.182/16
Vlan2 is down, line protocol is down
Hardware is Cat6k RP Virtual Ethernet, address is 0007.0001.0002 (bia 00d0.bcf1.ee5c)
cs-6506-24a#When you run Cisco IOS system software, the same commands apply for the VLAN (SVI) and L3 interfaces. The Layer 2 (L2) interfaces, however, have MAC addresses assigned from the range of MAC addresses in each module. Issue the show module command in order to see this range:
