Nexus 5k Peer Keepalive Link

[Steven Williams]

Can you move the peer-keepalive link after it already has been implemented? Is Cisco's recommendation to use the maangement ports on the 5k's rather than buring a 10G port for the keep-alive?                  

[Steve Fuller]

Hi Steven,

You certainly can move the peer-keepalive link after the vPC is established. This is effectively a peer-keepalive link failure which has no impact on the operation of the vPC. You can see this in the forum post where I've shown what happens when the peer-keepalive link is failed.

In terms of best practice on this, Cisco have it as second choice on a list of strong recommendations for the Nexus 7000 in the Recommendations for vPC Peer-Keepalive Link Configuration on page 27. I don't see any such strong recommendation for the Nexus 5000, but in my mind it's the obvious choice. We definitely don't want the peer-keepalive formed over the vpc peer-link so if we don't use the mgmt0 interface we must create a separate path to route this traffic across. If we use the mgmt0 interface we don't waste any physical ports on creating that separate link and we don't have to create SVI.

Where I'm working we've always used the mgmt0 interface via an out-of-band switch connection rather than building a separate link as it save on ports and we've never had any issues with it.

Regards

[David Lucas]

Hello,

Yes you can move the PKL, with no issue once the vPC is established. This is a zero impact if vPC is established.

In regards to where to connect it. Yes, as Steve mentioned it is the second choice on the Nexus 7000 to use the mgmt port. Some customers chose to use the mgmt port because they only have 10 gig in the chassis and don't want to burn ports on the PKL. The thing to remember is if you have redundant sups, to connect both mgmt ports (one will show down to the switch it is connected to). This will allow the PKL to still be up when a sup switchover occurs.

On the Nexus 5000 we typically see the mgmt port used for the PKL. The reason being is if you used a SVI and created a separate link then it'd break ISSU (there were some ways to make it work but not recommended). If you have a layer 3 module in the 5500s then you can burn a port in the Nexus 5548 and make it a routed port.

A majority of customers I work with that have N7K and N5K they would use the common dominator and use the mgmt port for PKL for both. This would be so there templates, and cabling were standardized.

With all that said, it is an unsupported design to have the PKL plugged into a FEX that is dual connected to a 5K (the FEX is vPC). If you think about it, it boils down to a chicken and egg issue where you need the FEX to come online for the PKL to come up, but to get the FEX online you need vPC to come up and to get vPC to come up you need the PKL. I tell customers to never connect the PKL into a FEX off the same pair. I have seen customers use Nexus for their OOB network...

Hope this helps to clarify.

Dave

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