DUP ICMP using HSRP

[Kevin15]

I"m having an issue and Cisco has "looked" at this issue and they think it might be a bug in the IOS but I'm not so sure.  I have a redundant Core and Distro layer using Nexus 9332's and 93180's respectfully.   I have set up HSRP on the Core's with all of the gateway's as x.x.x.1.  I have furthermore made Core 1 the Active for all Vlan's and Core 2 is the standby and I am using HSRP between the devices.   

I have maybe 9 interface vlan's and they are all configured with their own group #'s.  

When I ping certain devices whether from the Core or Distro switch there are multiple DUP's, sometimes up to 10 of them.   We thought we had an issue in our server farm but when I ping a user workstation from the Core or Distro I get DUP ICMP replies from them as well.   

Does anyone have an idea of what this could be?  I don't think it's just a bug in the software because sometimes they don't DUP.  

Any suggestions would be great!

[vishalbhandari]

@Kevin15 It sounds like you might be dealing with a Layer 2 loop or an issue with how HSRP is handling ICMP traffic. Since you're seeing duplicate replies from multiple devices (not just servers), I'd suggest checking the following:

1. Spanning Tree Protocol (STP) – Ensure there are no loops in your VLAN topology. Look for any blocked ports that might be intermittently forwarding traffic.
2. HSRP & ARP Issues – Verify that both Core switches aren't mistakenly responding to ARP requests at the same time. Try clearing the ARP cache (clear arp-cache) and see if it changes behavior.
3. MAC Flapping – Run show mac address-table to check if the same MAC is appearing on multiple interfaces, which could indicate a loop or a rogue device.
4. HSRP Preemption & Priority – Ensure that Core 1 stays the active router consistently. If there's frequent HSRP role switching, it might cause intermittent issues.

If the problem isn’t consistent, it may be tied to a specific event in the network, such as a device coming online or a topology change. Also, check if any devices have duplicate IPs using show ip arp | include x.x.x.1. Let me know what you find!