N9K-C93180YC-EX, vPC and routing protocols

[Seth Beauchamp]

I am planning to have a pair of N9K-C93180YC-EX running vPC to a router southbound and to another router northbound. I will need these two routers to peer with each other using ospf and bgp. I've previously had issues with routing protocols working through vPC but I feel like i recall cisco saying this was getting fixed in a new NXOS version. Can someone tell me if this is supported now and what NXOS version is necessary?

[josedelpino]

Hi Seth,

Just to clarify, the peering is only between the routers? and the Nexus will by providing Layer 2 connectivity to the routers? If this is the case it will work just fine, you dont need any particular NX-OS version.

Check page 77

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

If you want the peering beteween the Nexus and the routers, the best practice is to use individual L3 ports to each router instead of L3 VPC. If you still want to use L3 VPC in N9K you need at least NX-OS version 7.0(3)I5(1)

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

[Seth Beauchamp]

Correct, routing protocol between the two routers, both attached to the 2x 93180s with vpc toward the routers. I know there was a behavior where nxos decrements TTL by 1 when packets pass over the peer link, basically killing most routing protocols. Does that not happen when the protocol isn't terminating on a nexus switch?

[josedelpino · Accepted solution]

 "I know there was a behavior where nxos decrements TTL by 1 when packets pass over the peer link, basically killing most routing protocols"

You only need to worry about that when the peering is established between the Nexus and the routers. In your scenario the traffic beteween the routers will never go thought the vpc peer-link.