stp is easy; pick a central part of the diameter to be root (don't let the diameter choose; the human decides what is optimal), turn on stp and for redundant links, loop prevention is in effect...
mst requires configuration, and that configuration needs to be the same throughout the diameter... on a large network, mst requires planning and exactness... as it is being configured, there will be lags throughout the diameter... do not do this on a production network, for God's sake...
mst is compatible with the cisco default pvst+... ensure that the switches are in the default configuration...
dls1#sh spann
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
set the switches to a vtp domain same-name, and put them in transparent mode...
als1#sh vtp stat
VTP Version : 2
Configuration Revision : 0
Maximum VLANs supported locally : 128
Number of existing VLANs : 16
VTP Operating Mode : Transparent
VTP Domain Name : test
make vlans in all switches... vlan 30,40,50,60,70,80
als2(config)#vlan 30,40,50,60,70,80
als2(config-vlan)#
go into mst configuration mode and begin... note splitting up vlans per instance...
dls2(config)#spann mst config
dls2(config-mst)#name test
dls2(config-mst)#revision 1
dls2(config-mst)#instance 1 vlan 30,40,50
dls2(config-mst)#instance 2 vlan 60,70,80
dls2(config-mst)#sh current
Current MST configuration
Name []
Revision 0 Instances configured 1
Instance Vlans mapped
-------- ---------------------------------------------------------------------
0 1-4094
-------------------------------------------------------------------------------
dls2(config-mst)#sh pending
Pending MST configuration
Name [test]
Revision 1 Instances configured 3
Instance Vlans mapped
-------- ---------------------------------------------------------------------
0 1-29,31-39,41-49,51-59,61-69,71-79,81-4094
1 30,40,50
2 60,70,80
-------------------------------------------------------------------------------
dls2(config-mst)#end
sh current gives the configuration before, pending shows the configuration AFTER you write it with end or ctrl-z...
do this for each switch that should participate...
dls1#sh spann mst config
% Switch is not in mst mode
Name [test]
Revision 1 Instances configured 3
Instance Vlans mapped
-------- ---------------------------------------------------------------------
0 1-29,31-39,41-49,51-59,61-69,71-79,81-4094
1 30,40,50
2 60,70,80
-------------------------------------------------------------------------------
dls1#
i saved the best for last... you may choose to do this first, however... there will be lag as you incorporate the remaining switches
dls2(config)#spann mode mst
dls1#sh spann
MST0
Spanning tree enabled protocol mstp
Root ID Priority 32768
Address 0009.b73f.ce80
Cost 0
Port 7 (FastEthernet0/7)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32768 (priority 32768 sys-id-ext 0)
Address 000f.8ffe.0980
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7 Root FWD 200000 128.7 P2p Pre-STD-Rx
Fa0/8 Altn BLK 200000 128.8 P2p Pre-STD-Rx
Fa0/9 Altn BLK 200000 128.9 P2p Pre-STD-Rx
Fa0/10 Altn BLK 200000 128.10 P2p Pre-STD-Rx
Fa0/11 Altn BLK 200000 128.11 P2p
Fa0/12 Altn BLK 200000 112.12 P2p
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/19 Desg FWD 200000 128.19 P2p
Fa0/24 Desg FWD 200000 128.24 P2p
MST1
Spanning tree enabled protocol mstp
Root ID Priority 32769
Address 0009.b73f.ce80
Cost 200000
Port 7 (FastEthernet0/7)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 000f.8ffe.0980
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7 Root FWD 200000 128.7 P2p Pre-STD-Rx
Fa0/8 Altn BLK 200000 128.8 P2p Pre-STD-Rx
Fa0/9 Altn BLK 200000 128.9 P2p Pre-STD-Rx
Fa0/10 Altn BLK 200000 128.10 P2p Pre-STD-Rx
Fa0/11 Altn BLK 200000 128.11 P2p
Fa0/12 Altn BLK 200000 112.12 P2p
MST2
Spanning tree enabled protocol mstp
Root ID Priority 32770
Address 0009.b73f.ce80
Cost 200000
Port 7 (FastEthernet0/7)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32770 (priority 32768 sys-id-ext 2)
Address 000f.8ffe.0980
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7 Root FWD 200000 128.7 P2p Pre-STD-Rx
Fa0/8 Altn BLK 200000 128.8 P2p Pre-STD-Rx
Fa0/9 Altn BLK 200000 128.9 P2p Pre-STD-Rx
Fa0/10 Altn BLK 200000 128.10 P2p Pre-STD-Rx
Fa0/11 Altn BLK 200000 128.11 P2p
Fa0/12 Altn BLK 200000 112.12 P2p
dls1#
important points... all vlans are assigned to mst0 by default
dls2#sh spann mst config
Name [test]
Revision 1 Instances configured 3
Instance Vlans mapped
-------- ---------------------------------------------------------------------
0 1-29,31-39,41-49,51-59,61-69,71-79,81-4094
1 30,40,50
2 60,70,80
-------------------------------------------------------------------------------
dls2#
Pre-STD-Rx means that my 2950's are running a pre-ieee standard cisco proprietary version of mst... one of these days i'll do an ios upgrade... the 3550's are more current...
for more, here is an excellent discussion about mst on packet life:
http://packetlife.net/blog/2010/apr/26/multiple-spanning-tree-mst/
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