Nexus 7000 and vPC portchannel to an edge switch with EIGRP routers connected

[Ruterford]

Hello All,

I read that if there is an EIGRP running on an SVI on a nexus switch then you cannot be using this VLAN on vPC, this is a bit confusing to me, so I decided to ask a question here.

Currently I have two non-vss 6506 switches each connected to two edge switches and those edge switches are connected to a pair of routers that run EIGRP.So EIGRP adjacencies in this scenario are built in between the routers and 6506 switches over EIGRP enabled SVIs.

Now I need to replace the 6506 switches with two Nexus 7000s and I am wondering about the link in between the edge switches and new nexus swicthes.

I am confused whether I can use a port-channel and connect each single edge switch to both nexus switches using vPC port-channel on Nexus switch and regular portchannel on the edge switch or this is not going to work due to EIGRP issues.

Thanks!

[sean_evershed]

This post by Brad Headlund explains the issue. You will need a dedicated non-vPC link between the two N7Ks to carry your Layer 3 traffic.

http://bradhedlund.com/2010/12/16/routing-over-nexus-7000-vpc-peer-link-yes-and-no/

Fon't forget to rate all helpful posts.

[Ruterford]

Thanks Sean,

But this does not answer my question completely, i.e.

1) Can I connect both nexus switches to each Edge switch using vPC enabled port-channel on nexus switches?

or

2) I have to adopt the same approach as I was using for non-vss cat 6500 switches and connect each nexus to both edge swithces without utilizing cross-nexus chassis vPC portchannel

Thanks!

[glen.grant]

  Yes normally you can  attach a switch to a Nexus box via vpc .  Not sure about the EIGRP issue .

[Jon Marshall]

You can connect via a vPC but then you need to use a separate link between the Nexus pair for your routed traffic as Sean says.

Generally the recommendation is to use L3 routed connections to the Nexus pair ie. not a vPC then you do not need a separate link between the Nexus pair.

Jon

[Ruterford]

Jon,

Are you sure I can connect eac hedge switch to both nexus switches using vPC portchannel even if the VLAN that carries routed traffic (EIGRP) is trunked on that port-channel and is also an EIGRp enabled SVI on both nexus swicthes? Doesn't this mean that it will be loop-prevented as per Seans's submitted article?

Thanks!

[Jon Marshall]

Not sure i understand what you are asking ?

You can connect the edge switch with a vPC but then you need a separate link between the Nexus pair for that traffic ie. not on the vPC peer link.

The problem is that if you use a vPC and peer over that then the EIGRP neighbors are also seen across the peer link so traffic could be sent over the vPC to one Nexus switch and then have to be forwarded across the vPC link to the other Nexus.

If the traffic was then meant to be sent out of any vPC port it would be dropped because of the loop prevention mechanism used with vPCs.

Jon

[Ruterford]

From what I read, is that all vPC VLANs should be allowed on a vPC peer link.

If I connect using vPC each edge switch (that have EIGRP routers connected to them, say on VLAN 10), since I am using vPC portchannel for this trunk, I will end up having that VLAN 10 crossing in between the vPC peer link as well and it will break the loop-prevention. Isn't it true?

[Jon Marshall]

Yes, sorry i was getting two different scenarios mixed up.

You are absolutely correct in what you say and this is the reason you should not use a vPC if you are L3 peering with the Nexus switches.

You should connect your edge switch with L3 links which assumes obviously that vlans local to edge switch are routed on that switch. This way you avoid the vPC loop prevention issue.

Apologies for the confusion, my fault entirely.

Jon