spanning tree MST on Cat 6500, 4500, 3500

use the same network from previous lab, just remove the 3560 and Po64

let's focus on the two link between CORE1 and CORE2, and take VLAN 10, 20 as an example

before we go tot MST, there's something i forgot to mention on previous lab, this is one way to do the load balancing without using Etherchannel

CORE1#sh span vl 20

...

Interface        Role Sts Cost      Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Gi1/1            Desg FWD 4         128.1    P2p

Gi1/2            Desg FWD 4         128.2    P2p

Gi1/3            Desg FWD 19        128.3    P2p

CORE2#sh span vl 20

...

Interface        Role Sts Cost      Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Gi7/1            Root FWD 4         128.769  P2p

Gi7/2            Altn BLK 4         128.770  P2p

Gi7/5            Desg FWD 19        128.773  P2p

result for VLAN 10 also should be the same, so here's what we gonna do, we want to split VLAN 10 to use Gi7/1 and VLAN 20 to use Gi7/2,

and please take a close looks on port priority (in green), because we gonna manipulate this value the get the result

CORE1#sh span vlan 10

...

Interface        Role Sts Cost      Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Gi1/1            Desg FWD 4          16.1    P2p

Gi1/2            Desg FWD 4         128.2    P2p

Gi1/3            Desg FWD 19        128.3    P2p

CORE1#sh span vlan 20

....

Interface        Role Sts Cost      Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Gi1/1            Desg FWD 4         128.1    P2p

Gi1/2            Desg FWD 4          16.2    P2p

Gi1/3            Desg FWD 19        128.3    P2p

now the cost has changed, let's check on CORE2, VLAN 20 should have a different Root port by now

---------------- ---- --- --------- -------- --------------------------------

Gi7/1            Altn BLK 4         128.769  P2p

Gi7/2            Root FWD 4         128.770  P2p

Gi7/5            Desg FWD 19        128.773  P2p

now we go to MST

we'll  create

• a region REG1
• instance 1, VLAN 10, 30, Root no CORE1
• instance 2, VLAN 20, 40, Root on CORE2

CORE1(config)#spanning-tree mode mst
CORE1(config)#spanning-tree mst configuration
CORE1(config-mst)#revision 1
CORE1(config-mst)#name REG1
CORE1(config-mst)#instance 1 vlan 10, 30
CORE1(config-mst)#exit
CORE1(config)#spanning-tree mst 1 priority 8192

CORE1(config)#spanning-tree mst conf
CORE1(config-mst)#instance 2 vlan 20, 40
CORE1(config)#spanning-tree mst 2 prio 16384

run almost the same conf on CORE2, just change the priority for instance 1 and 2 to change the Root for each instance

CORE2(config)#spanning-tree mode mst

CORE2(config)#spanning-tree mst conf

CORE2(config-mst)#revision 1

CORE2(config-mst)#name REG1

CORE2(config-mst)#instance 1 vlan 10, 30

CORE2(config-mst)#exit

CORE2(config)#spanning-tree mst 1 priority 16384

CORE2(config)#spanning-tree mst conf

CORE2(config-mst)#instance 2 vlan 20, 40

CORE2(config-mst)#exi

CORE2(config)#spanning-tree mst 2 priority 8192

on Dist1, just run both of the instance

DIST1(config)#span mode mst

DIST1(config)#span mst conf

DIST1(config-mst)#rev 1

DIST1(config-mst)#name REG1

DIST1(config-mst)#inst 1 vlan 10, 30

DIST1(config-mst)#inst 2 vlan 20, 40

let's check is it working, by right, VLAN 10 Root is CORE1, 20 is CORE2

CORE2#sh span vl 10

MST1

  Spanning tree enabled protocol mstp

  Root ID    Priority    8193 bridge prio for VLAN 10 is 8193
             Address     0019.0787.3000

             Cost        20000

             Port        769 (GigabitEthernet7/1) via this port (CORE1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    16385  (priority 16384 sys-id-ext 1)

             Address     0019.a908.ac00

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

Interface        Role Sts Cost      Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Gi7/1            Root FWD 20000     128.769  P2p

Gi7/2            Altn BLK 20000     128.770  P2p  An alternate port is the next best path available back to the root bridge shall the root port fail

Gi7/5            Desg FWD 200000    128.773  P2p

CORE2#sh span vla 20

MST2

  Spanning tree enabled protocol mstp

  Root ID    Priority    8194

             Address     0019.a908.ac00

             This bridge is the root

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    8194   (priority 8192 sys-id-ext 2)

             Address     0019.a908.ac00

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

Interface        Role Sts Cost      Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Gi7/1            Desg FWD 20000     128.769  P2p

Gi7/2            Desg FWD 20000     128.770  P2p

Gi7/5            Desg FWD 200000    128.773  P2p Root bridge ports are all in FWD state


on DIST1

DIST1#sh span root

                                        Root    Hello Max Fwd

MST Instance           Root ID          Cost    Time  Age Dly  Root Port

---------------- -------------------- --------- ----- --- ---  ------------

MST0             32768 0018.19b2.58c0         0    2   20  15

MST1              8193 0019.0787.3000    200000    2   20  15  Fa4/3 root port for instance 1 (VLAN 10, 30)
MST2              8194 0019.a908.ac00    200000    2   20  15  Fa4/5 this is for instance 2

to confirm this, check which switch on Fa4/3 and Fa4/5

DIST1#sh cdp ne

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
CORE2            Fas 4/5           159             R S I  WS-C6509- Gig 7/5 now confirm that Instance 2 root is CORE2
CORE1            Fas 4/3           173             R S I  WS-C6509- Gig 1/3
 

happy Switching ;)