Is duplicate mac Normal?

[CiscoBro]

We have an environment with two VRF.

From the switch I see duplicate Mac's for different ip's in different VRF.

Is this Normal'

Address         Age       MAC Address     Interface
10.81.119.225   00:00:42  001c.7f60.6789  Vlan92
10.81.119.226   00:00:20  001c.7f60.6789  Vlan92
10.81.119.227   00:17:38  001c.7f60.6781  Vlan92
10.81.119.229   00:11:41  002a.6af1.1441  Vlan92
10.81.119.228      -      0000.0c9f.f05c  Vlan92
ruegtldrt002# show ip arp vlan 93

Flags: * - Adjacencies learnt on non-active FHRP router
       + - Adjacencies synced via CFSoE
       # - Adjacencies Throttled for Glean
       D - Static Adjacencies attached to down interface

IP ARP Table
Total number of entries: 4
Address         Age       MAC Address     Interface
10.81.119.249   00:00:43  001c.7f60.6788  Vlan93
10.81.119.250   00:05:06  001c.7f60.6788  Vlan93
10.81.119.251   00:17:23  001c.7f60.6780  Vlan93
10.81.119.253   00:18:32  002a.6af1.1441  Vlan93

Notice .253 and .229

Suggestions

[jj27]

Is it possible those MAC addresses are learned from another switch, which the bridge ID is that MAC?

[Rolf Fischer]

Hi,

the OUI 00-0A-6A belongs to Cisco, so we can assume the same Cisco (layer-3) neighbor-switch is connected through different VLANs.

Most Cisco switches use the same MAC address for all its SVIs, and as different VLANs are different broadcast domains as well, there's normally nothing to worry about.

For your reference:

http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6000-series-switches/41263-catmac-41263.html#topic1

HTH

Rolf

[InayathUlla Sharieff]

Agree with Rofl this is common to see on cisco switch so nothing to worry about.

You need to worry about duplicate mac when it is appearing on the logs which usually means a loop.

But in your case you are seeing it on the vlans which is good enough/expected. I have seen the mac address to be same on 100 vlans/intefaces.

Regards

Inayath