MST BPDU via EoMPLS Pseudowire Connections

[Chamindaw_2]

Hi All,

I've been trying to change the STP  mode of my MPLS aggrigation switches to MST due to many reasons but without success. (Currently all switches are working on PVST+.)

Below given my sample network topology, configurations on both switches and pseudowire configurations and error message.

ME3750(SW1) --- 7609 (EoMPLS pseudowire - VLAN 2500) 12406 -- ME3750(SW2)

Configurations

==========

ME3750(SW1)

=============

spanning-tree mode mst

spanning-tree extend system-id

!

spanning-tree mst configuration

name MPLS

revision 10

instance 10 vlan 2-99

instance 20 vlan 100-1999

instance 30 vlan 2000-4094

!

spanning-tree mst 0,10,20,30 priority 24576

!

!      

vlan 3,100,850,2500,3030

7609-PE

=======

interface GigabitEthernet0/1.2500

description *** MST_TEST ***

encapsulation dot1Q 2500

xconnect 10.2.0.5 2500 encapsulation mpls

end

ME3750(SW2)

===========

spanning-tree mode mst

spanning-tree extend system-id

!

spanning-tree mst configuration

name MPLS

revision 10

instance 10 vlan 2-99

instance 20 vlan 100-1999

instance 30 vlan 2000-4094

12406-PE

=======

interface GigabitEthernet2/1/0.2500

description *** MST_TEST ***

encapsulation dot1Q 2500

xconnect 10.1.0.8 2500 encapsulation mpls

end

There is a VLAN bsed EoMPLS configuration on VLAN 2500 on MPLS edges.

When the MST configuration done; the uplink trunk port of the ME3750(SW1) blocked with following erroe.

*Mar  1 02:45:11.920: %SPANTREE-2-PVSTSIM_FAIL: Blocking designated port Gi0/1: Inconsitent superior PVST BPDU received on VLAN 2500, claiming root 24576:001a.a2b5.7d00

While I googled, i found one post saying to change the priority of the MST regions to higher, hence forcing  one switch to become ROOT. Accordingly I changed the priority of ME3750(SW1) but still problem remains.

Can anyone of you experts help me out to get this sorted?

Note: I've not enabled native VLAN on both switches towards MPLE PEs and also hasn't enable any L2 protocols via speudowire connection.

Thank you all,

Chaminda

[Laurent Aubert]

Hi Chaminda,

The syslog message is because one of the switch is still running in PVSTP mode. Use the following command to make sure all the switch runs MST:

clear spanning-tree detected protocol

Now MST BPDU are sent in VLAN 1 (Native VLAN) so if this VLAN is not transported across the PW, it will not work. You should move to port mode or QinQ + L2 tunneling.

HTH

Laurent.

[jon.harald.bovre]

Change to port-based on PE like this:

7609-PE

int gig 0/1

xconnect 10.2.0.5 2500 encap mpls

12406-PE

int gig 2/1/0

xconnect 10.1.0.8 2500 encap mpls

When connecting MST regions to PVST+ or RapidSTP make sure root of vlan is IN MST region.

Better is lower, configure priority on MST switch to 0 (or lower than any PVST switch

But I see you are connecting two MST switches across pseudowire, problem are likely to be subinterface on PE

(we do not have configuration on CE towards PE)

problem should be solved by changing to port-based on PE's.

[Chamindaw_2]

Hi Jon,

Thanks for your reply. I'm having a practcal difiiculty of configuring port mode PW, since all my L2 & L3 customer connections interface with MPLS PE via same Gig port, further my requirement is to have local MST reigions per MPLS PE hence do not expect to pass through MST PBDUs via PW.

Anyway thanks for your responce again..

Chaminda

[Chamindaw_2]

Hi Laurant,

Thanks for your reply.

Actually  my requirement is to have local MST reigions per MPLS PE. That is why I  psecificaly block native VLAN passing through the PW and did not enable  any L2 protocols via PW.( believe this is a good practice.. ;-) )

BTW  I'll clear STP protocol as you suggested and see the results.

Also I can not configure port mode PW, since all my L2 & L3 customers interface with MPLS PE via this Gig interface.

My  understanding on MST BPDUs are passing through native VLAN. Hence in my  scenarion, if i'm not passing native VLAN throught the PW, what could  be the reason for blocking the entire port due to the "inconsistance  superior BPDU receive via VLAN 2500"?

Do I need to block STP on 7609 box itself? (read on one blog asking to disable STP on SUP720 on 7609)

Pl clarify.

Thank You,

Chaminda

[Laurent Aubert]

It seems you right. You need to disable STP on the 7600. Now from a design perspective, what you are doing could be dangerous if there is already a backdoor between the two MST region. Be sure this PW doesn't create any loops.

Thanks,

Laurent.

[Chamindaw_2]

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