MST and VRRP help wanted

[procurvenewbee]

Could someone elaborate as to what should be the correct behaviour when we connect an edge switch (say 2650) via tagged uplinks to two different distribution switches say 3524s, all switches running MST and 3524s running VRRP, with following configuration:

Switch 2650:

VLAN 1
VLAN10 (data) MST instance 1
VLAN 100 (Voice) MST Instance 2
VLAN 50 (Device Management) MST instance 1

Uplinks ports 23 to 3524A and 24 to 3524B with all of the above VLANs tagged.

Switch 3524A:

VLAN 1
VLAN 10 (data) MST instance 1 prio 0 & VRRP owner

VLAN 50 (Device Management) MST instance 1 prio 0 & VRRP owner


VLAN 100 (Voice) MST Instance 2 prio 1 & VRRP backup


A Layer 2 trunk to 3524B with VLAN 1, 10, 50, 100 tagged

Uplinks ports 24 to 2650, with VLAN 1, 10, 50 & 100 tagged.

Switch 3524B:

VLAN 1
VLAN 10 (data) MST instance 1 prio 1 & VRRP backup

VLAN 50 (Device Management) MST instance 1 prio 1 & VRRP backup

VLAN 100 (Voice) MST Instance 2 prio 0 & VRRP owner

A Layer 2 trunk to 3524A with VLAN 1, 10, 50, 100 tagged

Uplinks ports 24 to 2650, with VLAN 1, 10, 50 & 100 tagged.

I had assumed that MST will cause both uplinks from 2650 to be forwarding with one uplink carrying VLAN 10 (to 3524A which is VRRP active gateway for this VLAN) and other carrying VLAN 100 (to 3524B which is VRRP active gateway for this VLAN). I however find that only one uplink from 2650 is forwarding while other remains blocked. So all traffic will be going upstream via forwarding uplink (to 3524A) and then voice will then go to its gateway 3524B via the Layer 2 trunk between 3524A & B.

I have made 3524A as CST root with spanning-tree prio 0 and 3524B as CST backup root with spanning-tree prio 1 (though it shoudl not matter with MST which will use instance priority). Removing CST span priority does not make any difference other than show span will sometimes show CST root to be one of edge switch.

Can someone please supply some correct configuration applicable in this scenario? I will like to have one 3524A to act as gateway for data and other as gateway for voice vlan and then if one 3524 fails then remaining 3524 will become gateway for both data and voice.

Thanks a lot folks.

[Matt Hobbs]

From your description, you have configured it correctly. Did you check the actuall spanning-tree instances?

'show span instance 1' should show port X is forwarding and Y is blocked.
'show span instance 2' should show port Y is forwarding and X is blocked.

The regular 'show span' will show the CST and as you have seen, one link will be blocked.

[procurvenewbee]

Thanks Matt.

Yes I had checked with show span instance 1 and show span instance 2 and they show correct mapped VLANs but in both cases, the same uplink is used as forwarding (root) and the other one is blocking (alternate). Both instances on edge switch show 3524B to be the root MAC address and on each of 3524A & B, each one shows itself to be regional root. I had thought that I had made 3524A to be CST root with spanning-tree prio 0 and 3524B to be backup CST root with spanning-tree prio 1, but I may have removed it and at this point of time, they have following configuration:

On edge switches, I have
spanning-tree
spanning-tree proptocol-version mstp
spanning-tree config-name test
spanning-tree config-revision 10
spanning-tree instance 1 vlan 10 50
spanning-tree instance 2 vlan 100

On 3524A, I have

spanning-tree
spanning-tree proptocol-version mstp
spanning-tree config-name test
spanning-tree config-revision 10
spanning-tree instance 1 vlan 10 50
spanning-tree instance 1 prio 0
spanning-tree instance 2 vlan 100
spanning-tree instance 2 prio 1

On 3524B, I have

spanning-tree
spanning-tree proptocol-version mstp
spanning-tree config-name test
spanning-tree config-revision 10
spanning-tree instance 1 vlan 10 50
spanning-tree instance 1 prio 1
spanning-tree instance 2 vlan 100
spanning-tree instance 2 prio 0

Please advise.

Thanks

[procurvenewbee]

Further to this, if I add another edge switch with VLAN 20, 50 and 200 and uplink to the same distribution switches and distribution switches now updated as follows:

spanning-tree instance 1 vlan 10 20 50
spanning-tree instance 2 vlan 100 200

Will I have to have these two configuration lines on all of edge switches? So will the new edge switch have

spanning-tree instance 1 vlan 20 50
spanning-tree instance 2 vlan 200

or

spanning-tree instance 1 vlan 10 20 50
spanning-tree instance 2 vlan 100 200

and in latter case, all of existing edge switches will need to add these new VLANs and there span instance updated as above ??

Thanks

[procurvenewbee]

I have been doing some reading and it appears that I do need to create all VLANs within a MST region even if a switch does not have any port assignment for a VLAN. That will imply that if I have different edge switches with different VLANs needs (future needs), I will still set up all VLANs on all switches and then include all these VLANs on instances. I did look at mst-config and it shows same hash within region switches.

Still I do not understand as to what could be the problem in my present situation in which case, I do have same VLANs and thus all VLANs set up on edge switches and two distribution switches.

Further, in my case, Distribution switch A has been set up as MST root for instance 1 and Dist Sw B as MST root for instance 2. There is no CST root set up. And I am not sure if I set up Dist Sw A to be both a CST and MST root for the region will make any difference as there is no inter region or region to RSTP interaction (uplinks from distribution to two cores have stp disabled with bpdu-filter as there is layer 3 ospf between cores and distribution switches)

Any thing else I need to consider when setting up MST?

Thanks