duplicate MAC address on two switches

[thgusset]

Hi

we use vlan 3 as a management vlan to manage around 50 cisco switches.

We now found, that two Cisco Catalyst 4500 L3 switches uses the same MAC address (0008.e3ff.fc28) for the VLANs.

How can this be?

Thanks in advance

Thomas

[MHM Cisco World]

https://www.cisco.com/c/en/us/support/docs/switches/catalyst-6000-series-switches/41263-catmac-41263.html

This for 6000 series if yoh try apply same for 4500

MHM

[thgusset]

The problem is not that all VLAN interfaces have the same MAC address.

The problem is that two different switches have the same MAC address.

[MHM Cisco World]

In one SW or two SW, try config mac under vlan interface 

MHM

[thgusset]

config MAC on the VLAN interface is the solution to the problem.
But I wonder how it can happen that two switches use the same MAC address.

[MHM Cisco World · Accepted solution]

Issue with vpc abd vss

The vlan MAC drive from SW MAC'

Now when SW connect via vss the SW MAC is not use instead virtual MAC is use which drive from pool of mac +domain number

So if both site use same domain number there is chance of both VSS pair use same virtual MAC and hence same vlan mac.

I can easy suggest change domain but it can effect other protocol like stp so keep as it and manually config one site vlan mac 

MHM

[thgusset]

indeed the two switches use both switch virtual domain 10

this probably also explains problems with spanning tree

[Reza Sharifi]

Hi,

Are the core switches configured as VSS or StackWise Virtual?

HTH

[thgusset]

Hi

The core switches are independent switches on different locations (each has two SUPs with VSS). The switches are connected over a dark fiber based trunk.

Thomas