Setting a MAC address for spanning tree training

[irbk]

I'm doing some spanning-tree training and I'm wondering if it's possible, in the packet tracer software, to set the MAC address of a 3650 switch.  I don't want to just set 1 interface, because I want to control (not via priority but via MAC address) who is the root bridge of the network.  Is this possible in the packet tracer software and if so what's the command?

Thanks in advance! 

[vishalbhandari]

In Packet Tracer, you typically can't directly set the MAC address of a switch. The MAC address is usually automatically generated based on the hardware of the virtual device.

However, if you want to control the selection of the root bridge in a Spanning Tree Protocol (STP) environment based on MAC address, you can influence it indirectly by adjusting the priority of the switches.

[irbk]

Yes, I'm aware that I could adjust root bridge based on priority but this is for training purposes so I want the priorities to be the same.  Just to make it easier for training, I would have liked to be able to set the MAC addresses to something like aaaa.aaaa.aaaa, bbbb.bbbb.bbbb, cccc.cccc.cccc, etc, so that it was obvious which switch would become the root bridge.  It's a lot easier/faster for people just learning spanning tree concepts to see that aaaa.aaaa.aaaa is the root bridge than looking at  00:06:2A:B1:90:06, 00:E0:B0:4D:75:78, 00:0B:BE:77:EC:8B, etc. and trying to figure out which one is going to be the root bridge.  Forcing them to figure out who is the root bridge with actual MAC addresses is more "real world" for sure but when you're introducing the topic of spanning-tree, I think it's best to start out by making things a bit more obvious.  Then once the basic concepts are grasped, start introducing the more 'real world' stuff.  

[MHM Cisco World]

Friend dont confuse with MAC address of SW in STP domain 
the SW priority have most highest bit, so even if SW with high mac address and low priority it will not elect 
so instead of play with MAC play with priority.

MHM

[irbk]

Yes, I'm aware.  The point of the lesson is that, with all switches having the same priority, the MAC address is the tie-breaker for determining the lowest bridge ID.

[MHM Cisco World · Accepted solution]

Most significant bits is import so start check  mac of each SW from left side  i.e. same idea of priority not need to see whole Mac check only left bits

MHM

[irbk]

True, I could just use the first few bits of the MAC and that's likely what I'll do since I can't adjust the MAC within packet tracer.  Just IMHO but its still easier to see that AAAA is lower than BBBB or CCCC than it is to see that 0006 is lower than 00E0 or 000B.  Again, when you're attempting to teach something new to someone, limit having to make them think about the non-important things.