Nexus vPC | Routing over vPC

Let me tell you a sad story...

Some time ago, I ran into a problem. I was in the data centre all night and nearly pulled my hair out in frustration. No matter what I tried, I couldn't get vPC to work with #OSPF or #EIGRP

Let me save you this pain, and show you the pitfall of routing over #vPC, and how to avoid it, using layer-3 peer-router

This video is particularly helpful to network engineers working with vPC in production.

Also useful for CCNP Data Center, and CCIE Data Center

Part 1: How vPC Works - vPC adds redundancy to the data centre, while avoiding the older technologies like spanning-tree. See how it fits into your solution, and parts under the hood

Part 2: vPC Configuration - Now you know how vPC works, you can start configuring. See how it's done by watching live config on real Nexus switches

Part 3: Routing over vPC - Be careful! There are pitfalls when running routing protocols over vPC! I fell into one of these myself. See how you can avoid this

Some platforms now support hitless vPC role changes.

300-180 DCIT
300-160 DCID
300-165 DCII
layer3 peer-router

[xeifora]

I love your storytelling combining with the real-time troubleshooting approach, that's really helped me a lot to understand the whole situation on how to apply dedicated command regarding your scenario. Great video !!

[kellymoses]

This issue is fundamentally caused by the fact that vPC makes two switches look like one device at layer 2 but NOT at layer 3.

[ibrennan]

Excellent video, it took me weeks of research to fully understand what you explained in minutes. I have a similar project where we were having issues with EIGRP, "layer3 peer-router" fixed it!

[francescogalli]

Really loved it
That is exactly what I've experienced last week after an upgrade to nxos 7.3.7 with eigrp
Lucky me, i remembered your video
Thanks

[chetanpadshala]

That is really good information on Routing Over VPC. Short, Simple and Amazing information. Thank you.

[shawn_]

Thx a lot for sharing your issue, will keep note of this.

[CiscoPhipse]

Thanks 👍
You kept us waiting a while for this video 🙂

[ElGuapoSalsero]

Thank you for this video as it served as a sanity check. I’m having an issue where a port-channel has 2 links to an adjacent firewall and both sides are forming a BGP adjacency and the peering is stable. However, when both port-channel members are UP, there are packet drops seen when trying to reach a loop back interface on the firewall. If I disable the port-channel link going to VPC with secondary role, the traffic to the loopback stabilizes. I saw you have the command ip arp synchronize which I do not have. What does that command do beyond the obvious inference? Do you think this may help?

[rajpjunior]

heheh I like how it begins. "Oh, the horror!!! Routing and
:-D

[motiamiful]

does this solution of applying the 'layer3 peer-router' command is suitable for multicast traffic as well?
BTW - great video great explanations!

[musalyh]

4:20 sw2 and router connected interfaces are different networks?? As far as I know, the TTL is not reduced for the same network. Therefore, if it is the same network, the TTL will not be 0, so I don't think there is a problem with OSPF. What do you think in my opinion?

[Soundwave-FZ]

thanks for the video. we have a pair of vpc 9ks that we're attempting to do BGP neighborship with an active/standby ASA so they can excahange routes. Do you recommend we that we use the same AS on both the 9ks or different AS numbers?

[OkaKeanu]

Thanks, How configuration EBGP from VPC to VSS switch, should we use L2 link or L3 link ?should we have additional link between vpc switch ?

[alihabib]

Could you please share the full config of the topology

[headdstrong]

Thanks for video.How do i announce my subnet in ospf in nx-os.For example: in isr router press command network 10.1.1.0 0.0.0.255 area 1
But in nexus not found this command

[AH-psuv]

So in summary from what i have understood:

it is the purpose that the router forms a neighborship with only one of the NX-OS devices that are bundled in the VPC domain. even thought both the NX-OS devices act as 1 device

It can happen that the router sends IGP related data to the other NX-OS device ( because of the LAG hashing algortihm)

With the peer-router command configured on the NX-OS devices this is no problem because the NX-OS device that receives the IGP related data which was not ment for him, he will send it over the peer-link to the other NX-OS device. But the problem is that he will decrement the TTL which in many times with IGPs is 1 (so it will become 0 and hence discarded), so the NX-OS device for which the IGP related data was ment never receives it.

result = IGP neighborship flapping

solution: add layer3 peer-router command or increase the IGP ttl to 2.

does this describe the issue correctly?

[mauricewalker]

So the big question on everybody's mind is if I add the layer3 peer router command to both switches will traffic be interrupted? I have this exact issue with my edge switch and I'd like to fix it during a maintenance window but I need to tell my business if there's going to be a possible downtime. Thx.

[Emerb]

These videos are everything. I have to connect two 5k (5548, 5596) to a Nexus 2k in the morning. From your video's can I connect the 2k to Vlan 20?