OSPF Routing over VPC

[ar]

I have Nexus 9500s and 9300s.

VPC enabled.

A router below is dual-homed to the 9300s.

I would like to establish IGP adjacency as below.

Is this a supported topology?

How will be the behavior of OSPF neighbors, failover in this case?

Please advise, thanks

[kbmorris21]

Unfortunately it is not supported to run any dynamic routing protocol over vPC to the vPC switch. This is because of the conflict in Layer2 path selection by the port channel and Layer3 path selection by the routing protocol. Once a frame enters on one vPC interface it is not allowed to cross the vPC Peer Link; and cannot reach the interface of the vPC neighbor. It leads to a lot of dropped traffic when the L2 and L3 decisions do not match.

[ar]

I have updated the diagram for clarity.

Based on the diagram, I thought from the persepective of router below it can form adjacency to both VPC switches (N9500s) on each leg - total of 4 adjacencies. Haven't simulated yet though.

Can your share any docs pertaining to restrictions running  dynamic routing protcol over VPC to the VPC switch?

[kbmorris21]

https://www.cisco.com/c/dam/en/us/td/docs/switches/datacenter/sw/design/vpc_design/vpc_best_practices_design_guide.pdf

Starting at page 81 are the Unsupported Layer3 Designs. The design you propose is Figure 60 (roughly).

[ar]

thanks kbmoris.

I have read in the NX-OS config guide as well that attaching a layer3 device  in a L2 VPC path is not recommended.

thanks for your assistance.