Hey guys!! Whats up!?
There's just nothing better than a core migration brainstorming session to start your monday in a good mood right? Grab your coffee and join me!! 
So, one of our clients bought two Nexus 7010 and want to migrate their core layer from a 3Com 7910 running MST to this new pair of Nexus 7010.
Here is the before topology: http://imgur.com/oSQndSz,xCkIxQj#1
As you can see core-a and core-b are both 3com. They run MST with 2 instances (actually 3 but they don't use instance 0). And here is the problem that I need your help. Today their mst instances are configured like this:
instance 1, vlans 2-5
instance 2, vlans 6-700
This is how I have to connect the new pair of Nexus 7010. By contract I have to connect at least those links you see.
New topology: http://imgur.com/oSQndSz,xCkIxQj#0
Both Nexus 7010 at some point in time need to become the new Core and the old 3Com will be positioned as just another access switch. I can think of two strategies so far regarding this MST configuration.
1- During a MW just tune the priorities so N7Ks are the new root bridge and wait (and pray a lot). I expect downtime on every vlan since MST will have to recalculate itself. I will even lose management since they do in-band. That's scary!
2- Create two other MST instances making N7K-1 (left) being root of one and N7K-2 (right) being the root of the other, and during the MW I'll have to tune these new instances vlan member's so only a very few specific vlans will have downtime. The problem is that this strategy requires a lot more effort since I'll have to change this vlan membership in every switch in this domain.
I didn't show on either topology but there are servers connected to both 3Com, both 5596 and both 6506. And lot's of access switches connected to both 3Com.
Am I missing something? What would you guys do? Any recommendations?
Sorry if this kind of post is not supposed to be in this forums. Just let me know and I'll remove it.
Thanks!!
