Trying to understand when you can and can't vPC

[Steven Williams]

I have a pair of 4500x running in vss mode. I would like to run Layer 3 port channel to a nexus 5548 pair running in vPC mode, IP address on portchannel interface on the 4500x pair only. Then nexus 5k would run  Layer 2 vpc on same links connected to the 4500x Layer 3 portchannel links. Then I would put a SVI on nexus 5K in same subnet as Layer 3 portchannel on 4500x. Then allow that vlan on the layer 2 vPC to the Pair of 4500x's and run an eigrp instance between them. So the Nexus 5k pair would peer to each other over the vPC peerlink which is supported per the link pasted below, and each Device in the Nexus pair would peer with the 4500x VSS pair as it would look like just one device downstream.

http://www.cisco.com/c/en/us/support/docs/ip/ip-routing/118997-technote-nexus-00.html

Can this be done? Is it a Cisco Support topology?

[cj.johnson3cigna]

You cannot have a Port-Channel with one side L3 and the other side L2. Why not make the Port-Channel L2 then create SVIs on both sides?

[Steven Williams]

Sorry that's what I meant. The way the documentation reads is that connecting a Layer 3 device via vPC is not supported. But the 4500x is not a router of firewall like the document states. You can configure the ports to be layer 3 like a router but essentially the 4500 is a switch.

So yes I would create a /30 subnet between the Nexus and 4500s with SVIs on each end and only trunk that that routed vlan. This will then achieve MEC from the 4500 to the Nexus 5k and vPC from the Nexus 5k to the 4500.

[cj.johnson3cigna]

Yes, that would work.

I agree that the documentation is confusing. What they are trying to express is that you cannot configure a vPC in L3 mode like you can if you're doing something like VSS or StackWise, which are Catalyst technologies not available on Nexus.