[c-nsp] Quick spanning-tree and bridge-group question

[Sam Stickland]

Sam Stickland wrote:
> Peter Rathlev wrote:
>>
>> Isn't port priority the last thing the Spanning Tree Algorithm looks at?
>> AFAIK the selection of root port should be, in order: Root Bridge ID,
>> Port Path Cost, Sending Bridge ID and at last Sending Port ID, which is
>> Port Priority and Port Index.
>>
>> Are the three ports all pointing towards the root bridge?
>>   
> Yes, all three ports are pointing towards the root.  You are right, I 
> had remembered the order wrong. At least something like this causes it 
> to sink it. (I would test it but I'm having trouble convincing one of 
> the other routers to change it's bridge identifier on the BVI :| )
>
Well I finally convinced the router to change it bridge id (had to 
change the mac-address on all physical interfaces - even those not in 
the bridge group!), but I still don't see the result I'd expect:

R1#sh spanning-tree

 Bridge group 10 is executing the ieee compatible Spanning Tree protocol
  Bridge Identifier has priority 32768, address 0013.8050.b191
  Configured hello time 2, max age 20, forward delay 15
  Current root has priority 10, address 0019.aa7f.3480
  Root port is 28 (Serial0/0/0.10), cost of root path is 723
  Topology change flag not set, detected flag not set
  Number of topology changes 34 last change occurred 00:02:09 ago
          from FastEthernet0/1.161
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 0, topology change 0, notification 0, aging 300

 Port 26 (FastEthernet0/1.161) of Bridge group 10 is blocking
   Port path cost 647, Port priority 128, Port Identifier 128.26.
   Designated root has priority 10, address 0019.aa7f.3480
   Designated bridge has priority 32929, address 0019.aab4.f700
   Designated port id is 112.3, designated path cost 76
   Timers: message age 6, forward delay 0, hold 0
   Number of transitions to forwarding state: 6
   BPDU: sent 870, received 7351

 Port 27 (FastEthernet0/1.162) of Bridge group 10 is blocking
   Port path cost 647, Port priority 128, Port Identifier 128.27.
   Designated root has priority 10, address 0019.aa7f.3480
   Designated bridge has priority 32930, address 0019.aab4.f700
   Designated port id is 112.3, designated path cost 76
   Timers: message age 5, forward delay 0, hold 0
   Number of transitions to forwarding state: 2
   BPDU: sent 862, received 7330

 Port 28 (Serial0/0/0.10) of Bridge group 10 is forwarding
   Port path cost 685, Port priority 144, Port Identifier 144.28.
   Designated root has priority 10, address 0019.aa7f.3480
   Designated bridge has priority 32768, address 0055.aa7f.3480
   Designated port id is 128.20, designated path cost 38
   Timers: message age 4, forward delay 0, hold 0
   Number of transitions to forwarding state: 6
   BPDU: sent 552, received 14515