MST-TO-RAPID-PVST COMMUNICATION

[stephn.zii]

Hello all,

I am trying to setup a communication between mst and rapid-pvst. I have two switches connected to each other one has mst instance 5 with two vlans (3,4) and the other switch has rapid-pvst with same vlans. I have setup vlan interfaces on both switches but communication between vlans across the trunk interface between the switches is not working, I cannot ping from one vlan to the other. 

Config on SW7:

!
interface Ethernet0/1
switchport trunk encapsulation dot1q
switchport mode trunk

SW7#sh spanning-tree vl 3

VLAN0003
Spanning tree enabled protocol rstp
Root ID Priority 32771
Address aabb.cc00.0500
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32771 (priority 32768 sys-id-ext 3)
Address aabb.cc00.0500
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Et0/1 Desg FWD 100 128.2 P2p

SW7#sh spanning-tree vl 4

VLAN0004
Spanning tree enabled protocol rstp
Root ID Priority 32772
Address aabb.cc00.0500
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32772 (priority 32768 sys-id-ext 4)
Address aabb.cc00.0500
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Et0/1 Desg FWD 100 128.2 P2p

Config on SW8

!
interface Ethernet0/0
switchport trunk encapsulation dot1q
switchport mode trunk

SW8#sh spanning-tree vl 3

MST5
Spanning tree enabled protocol mstp
Root ID Priority 32773
Address aabb.cc00.0600
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32773 (priority 32768 sys-id-ext 5)
Address aabb.cc00.0600
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------

SW8#sh spanning-tree vl 4

MST5
Spanning tree enabled protocol mstp
Root ID Priority 32773
Address aabb.cc00.0600
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32773 (priority 32768 sys-id-ext 5)
Address aabb.cc00.0600
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------

Looking at the output above the interface is not showing for SW8, any help how I can get these two to communicate is appreciated

Thank you.

[balaji.bandi · Accepted solution]

Good cisco document running multple STP instances :

https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/24248-147.html#migration_strategy

This was notes from my Lab long back : (dont have access to lab to test) - but this should give you idea to fix :

I am running VTP Tranparent :

SWITCH 1 : MST
===========================
spanning-tree mode mst
spanning-tree extend system-id
spanning-tree backbonefast
!
spanning-tree mst configuration
instance 1 vlan 10, 20, 30
!
spanning-tree mst 0-1 priority 24576
!
!
vlan 10,20,30

SWITCH 2 : rapid-pvst :
============================
spanning-tree mode rapid-pvst
spanning-tree extend system-id
!
!
vlan 10,20,30

SW1#show spanning-tree vlan 10

MST1
Spanning tree enabled protocol mstp
Root ID Priority 24577
Address aabb.cc00.0c00
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 24577 (priority 24576 sys-id-ext 1)
Address aabb.cc00.0c00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Et0/3 Desg FWD 2000000 128.4 Shr Bound(PVST)

SW2#show spanning-tree vlan 10

VLAN0010
Spanning tree enabled protocol rstp
Root ID Priority 24576
Address aabb.cc00.0c00
Cost 100
Port 4 (Ethernet0/3)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32778 (priority 32768 sys-id-ext 10)
Address aabb.cc00.0a00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Et0/3 Root FWD 100 128.4 Shr Peer(STP)

[stephn.zii]

Hello Bandi,

I did run a new lab with your config and everything worked there was it supposed to. Thank you very much for the help.

[balaji.bandi]

no worries glad it helpful, we make this as a solution now.

[MHM Cisco World]

I will run lab and share with you update 

[stephn.zii]

Hello MHM,

Please let me know when you have an update I will like to compare and see if I did miss anything or if there are other ways of setting this up.

[MHM Cisco World · Accepted solution]

 I run lab 
config MST instance one for each VLAN 
config PSVT in other SW 
config trunk port WITH allow vlan 1,10,20 (VLAN1 must allow )
and it work and I can ping SVI from SW to other.

can you share more detail about your config ?

[paul driver · Accepted solution]

Hello
You OP just shows that you have an MST region (mst sw8) and non MST PVST region (rstp sw7) interconnected. The reason you are seeing root on both switches is that the common spanning tree (CST) link between these stp domains will run over sw8 (MST5) or (MST0) for non defined vlans and sw7 (vlan1).

As such stp root bridge election from sw8 perspective it will be via mst 5, and from sw7 perspective it will be over vlan 1, this stp root is called common instance spanning-tree-  CIST)

Sw8
show spanning-tree mst 5

Sw7
show spanning-tree vlan  1