Duplicate address across VPC peer-link on Nexus 7010

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Jan 4th, 2010
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Just set up a VPC peer-link between two 7010 switches.  The peer-link is a port-channel of two 10Gb connections.  On both sides I'm seeing this in the log:

2010 Jan  5 04:27:34 CRMCN7K-1 %ARP-2-DUP_SRC_IP:  arp [3069]  Source address of packet received from 0024.f716.b341 on Vlan401(port-channel10) is duplicate of local,

and on the other

2010 Jan  5 04:23:39 CRMCN7K-2 %ARP-2-DUP_SRC_IP:  arp [3052]  Source address of packet received from 0024.f71f.a7c1 on Vlan401(port-channel10) is duplicate of local,

VLAN 401 is the only VLAN on them right now with a Layer 3 address.  What am I missing?  Everything looks correct.  Port-Channel10 is up and running fine..or so it seems.

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nashwj Mon, 01/04/2010 - 17:09
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Hrmmm...  I really don't think so but I'll check again tomorrow.  Nothing responded to pings on those IPs when I double-checked them today.  But, we'll see.

nashwj Tue, 01/05/2010 - 07:41
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Checked it this morning by making a new VLAN and assigning a fake IP,  Instantly started getting this in the log:

CRMCN7K-1(config-if)# 2010 Jan  5 21:41:53 CRMCN7K-1 %ARP-2-DUP_SRC_IP:  arp [3069]  Source address of packet received from 0024.f716.b341 on Vlan402(port-channel10) is duplicate of local,

So a dupe IP isn't it.

Reza Sharifi Tue, 01/05/2010 - 08:20
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Not familiar with Nexus, but if you are creating VPC, shouldn't be just layer-2 link?

vPC Layer 3 Interaction

Although vPC is primarily a Layer 2 technology, the Cisco Nexus 7000 Series Switches are also full-featured Layer 3 network devices
Jerry Ye Tue, 01/05/2010 - 19:54
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What version are you running? Is DHCP feature enabled?



mrahman71 Tue, 03/16/2010 - 10:08
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I'm having the same issue , and it seems that it is related to the DHCP feature being enabled on the 7000 .. I'm running version 4.1 (4)....

Any clues ?

Hey Nashwj,

What version of NX-OS are you running?

Are the 7K in a stand alone environment (lab or similar) or connected to other production network devices?

Are both of the VLANs carried across the vPC peer link port-channel?

Are both of the VLANs carried across any vPC port-channel?

Do you have HSRP setup on the VLAN 401 interfaces on each of the 7Ks?  If so, what are the real and vip IP addresses?

If you can either provide answers to the above or configuration snapshots of the vPC and SVI interfaces for your VLANs on each of the 7Ks a solution should be reachable.

atl5150atl Wed, 03/10/2010 - 06:07
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I have a problem similar to the original poster's.  I'm attempting to connect a point to point circuit and get the same ARP errors and duplicate ip address warnings.  It appears (to me) that there is a loop on the provider's side of the circuit, but they claim there isn't.

Has anyone else seen this or troubleshot this?  Thanks


atl5150atl Tue, 03/16/2010 - 10:14
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UPDATE (Not a real solution though!)

After swearing up and down that our circuit was not looped, it appears that our service provider DID have it looped.  Hope your answers are just as easy to find.  I will say that the error was pretty much what it said it was.  That is to say, the switch saw it's own IP come back to it via an EIGRP hello.  You'd think there would be a safegaurd against that...


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