MST

Set up MST out of the BCMSN lab portfolio tonight.... I did it off of 3 switches though, and they had me run through what I thought was a pretty basic configuration of MST. 3 switches, all interconnected in a triangle fashion. All had vlans 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100. With per-vlan stp you basically had an instance running for each, 11 in total. All instances were computing the same stp topology, over the same physical connections. A bit redundant ehe?@?
So MST lets you "group" these vlans. Heres what I did with some output omitted of course:

POE(config)#spanning-tree mode ?
mst Multiple spanning tree mode
pvst Per-Vlan spanning tree mode
rapid-pvst Per-Vlan rapid spanning tree mode

POE(config)#spanning-tree mode mst
POE(config)#spanning-tree mst ?
WORD MST instance range, example: 0-3,5,7-9
configuration Enter MST configuration submode
forward-time Set the forward delay for the spanning tree
hello-time Set the hello interval for the spanning tree
max-age Set the max age interval for the spanning tree
max-hops Set the max hops value for the spanning tree

POE(config)#spanning-tree mst config
POE(config)#spanning-tree mst configuration ?


POE(config)#spanning-tree mst configuration
POE(config-mst)#?
abort Exit region configuration mode, aborting changes
exit Exit region configuration mode, applying changes
instance Map vlans to an MST instance
name Set configuration name
no Negate a command or set its defaults
private-vlan Set private-vlan synchronization
revision Set configuration revision number
show Display region configurations

POE(config-mst)#sh current
Current MST configuration
Name []
Revision 0 Instances configured 1

Instance Vlans mapped
-------- ---------------------------------------------------------------------
0 1-4094
-------------------------------------------------------------------------------
POE(config-mst)#sh pending
Pending MST configuration
Name []
Revision 0 Instances configured 1

Instance Vlans mapped
-------- ---------------------------------------------------------------------
0 1-4094
-------------------------------------------------------------------------------

POE(config-mst)#name ?
WORD Configuration name

POE(config-mst)#name cisco ?


POE(config-mst)#name cisco
POE(config-mst)#revision ?
<0-65535> Configuration revision number

POE(config-mst)#revision 1

POE(config-mst)#instance 1 ?
vlan Range of vlans to add to the instance mapping

POE(config-mst)#instance 1 vlan ?
LINE vlan range ex: 1-65, 72, 300 -200

POE(config-mst)#instance 1 vlan 20-50
POE(config-mst)#instance 2 vlan 80, 100
POE(config-mst)#sh pending
Pending MST configuration
Name [cisco]
Revision 1 Instances configured 3

Instance Vlans mapped
-------- ---------------------------------------------------------------------
0 1-19,51-79,81-99,101-4094
1 20-50
2 80,100
-------------------------------------------------------------------------------
POE(config-mst)#exit

POE#sh spanning-tree mst config
Name [cisco]
Revision 1 Instances configured 3

Instance Vlans mapped
-------- ---------------------------------------------------------------------
0 1-19,51-79,81-99,101-4094
1 20-50
2 80,100
-------------------------------------------------------------------------------

Now when I run a simple show spanning-tree I will basically see 3 instances (i.e. 3 stp calculations) versus the 11 we saw earlier. Brilliant! I also did a bit of unplugging as I went with some different debugs running. The best command I hit was debug spanning mst roles. Great output.