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New Member

ASR9000 Layer 2 Integration with 7600


I have a problem integrating 2 x ASR9000 with 2 x 7600

The topology is Just simple


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ASR 9000 is running MST , while 7600 is running PVST all attached using a Single Tengig Interface.

The problem I have that i can see there are two roots - A root per each Protocol Rootbridge for MST and root for PVST

Is there a specific best practice for integration in such, I need to run it  using spanning tree , as PVSTAG will not be included in spanning tree Algorithm , and i was not able to connect a server dual homed to the two 9ks.


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Cisco Employee

ASR9000 Layer 2 Integration with 7600


The mixing of STPs can get tricky.  Now depending on your MST config you could see a root for MST CIST and then different roots for the PVST vlans that are not included in the CIST.

Here is a decent doc on MST and integrating it with PVST.

Simply put, we should see all roots in MST region or just CIST in MST and ALL other vlans not included in CIST need to be seen as a root in MST or PVST.  Can't be mixed. 

If you want to include snippets of your MST and PVST configs we can look at it further.



New Member

ASR9000 Layer 2 Integration with 7600

On both ASR9K:

spanning-tree mst Trust_sig

name Trust_sig

revision 1
instance 0
   priority 32786
instance 1
   vlan-ids 100,200
   priority 32786


interface GigabitEthernet0/0/0/2


interface GigabitEthernet0/1/0/2



bridge group Trust_sig

bridge-domain Trust_sig1

interface GigabitEthernet0/0/0/2

interface GigabitEthernet0/1/0/2

On 7600 its normal PVST configuration with priority 0 on 7600(1)

Is there any specific thing i need to do from PVST side or from MST side? also now i am having a spanning tree loops.

I need to insure interoperability between both sides , and also that 7600(1) always act as the root for vlan 100 and vlan 200

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