C9300-24P Switch MAC Address Duplication

[id404]

I have two C9300-24P switches stacked together. After unstacking them and placing them in different server rooms, I found that the MAC addresses of VLAN 20 on both switches are exactly the same, causing one of the switches to become unmanageable. How should I handle this situation?

[Kasun Bandara]

hi@id404 , are those switch configs defaulted before deploy in new place? also can you remove and readd the VLAN 10 to see the impact?

[sidshas03 · Accepted solution]

Hey,

When you split a Catalyst 9300 stack, both switches keep using the same base MAC address that was originally assigned to the stack. That’s why you’re seeing the same VLAN 20 MAC on both, and it’s creating a conflict on the network. The clean way to handle this is to reload the switches after breaking the stack, so each one will generate and use its own system MAC again. If they still come up with the same address, you can manually clear the old stack configuration (like removing any leftover switch stack settings) and then reload. After that, each switch should have its own unique VLAN MAC and you won’t run into the duplicate issue.