Same MAC on 2 Different Devices?

Unanswered Question
Apr 28th, 2010

Hello:

Is it possible to have two separate servers with the same MAC address?

I have 2 separate switches that have the same MAC address on an access port in the same VLAN. The MACs belong to 2 different Sun stations. Or could this be the same machine and the same NIC with two active connections to 2 separate switches?? The description on the ports dont suggest that, but that may mean nothing at all.

Thanks!

Sw2#sh mac-address-table | in GigabitEthernet3/3
450    0014.4f41.3b8e   dynamic ip                    GigabitEthernet3/3

interface GigabitEthernet4/18
description v08k410-ipmp1 15102 021110 mm
switchport access vlan 450
speed 1000
duplex full
end

========================================================================


Sw1#sh mac-address | in GigabitEthernet4/18
450    0014.4f41.3b8e   dynamic ip                    GigabitEthernet4/18

interface GigabitEthernet3/3
description v08k410-ipmp2 15102 031210 mm
switchport access vlan 450

I have this problem too.
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Leo Laohoo Wed, 04/28/2010 - 20:24

IT is possible when both interface go to the same physical client.  Have you verified visually?

ex-engineer Wed, 04/28/2010 - 20:36

Do you mean that one machine can have a NIC with 2 active connections to 2 different switches? Is that what youre implying may be the problem?

Leo Laohoo Wed, 04/28/2010 - 22:54

I'm not saying that this is your problem but I've seen some cases where two NICS come from the same Sun client sport ONE common MAC address.  In some cases, only one MAC address is used and the other acts "dumb".

Ganesh Hariharan Wed, 04/28/2010 - 23:10

Hello:

Is it possible to have two separate servers with the same MAC address?

I have 2 separate switches that have the same MAC address on an access port in the same VLAN. The MACs belong to 2 different Sun stations. Or could this be the same machine and the same NIC with two active connections to 2 separate switches?? The description on the ports dont suggest that, but that may mean nothing at all.

Thanks!

Sw2#sh mac-address-table | in GigabitEthernet3/3
450    0014.4f41.3b8e   dynamic ip                    GigabitEthernet3/3

interface GigabitEthernet4/18
description v08k410-ipmp1 15102 021110 mm
switchport access vlan 450
speed 1000
duplex full
end

========================================================================


Sw1#sh mac-address | in GigabitEthernet4/18
450    0014.4f41.3b8e   dynamic ip                    GigabitEthernet4/18

interface GigabitEthernet3/3
description v08k410-ipmp2 15102 031210 mm
switchport access vlan 450

Hi,

It can be possible that sun server two NIC are connected with two different swiches ports and at SUN server end teaming would be configured with ACTIVE/ACTIVE fashion.That can also be the reason mac is getting learned from both the switches.

Hope to Help !!

Ganesh.H

ozzyosbu1 Wed, 04/28/2010 - 23:23

SW1 and SW2 may be connected back-to-back using access ports in VLan 450 ( rather than using a Trunk)

ex-engineer Thu, 04/29/2010 - 06:59

Thanks, folks.

Quick question, though.

This kind of error message is typically seen when there is a bridging loop. I dont think there is one given all the info I have shown you. However, how does one go about finding out if an intermittent bridging loop is occurring throughout the day? What forensice are available? In other words, how does one rule out or rule in, for that matter, that a bridging loop has occurred?

Thanks

abmehta Thu, 04/29/2010 - 09:55

Hi

The best way to determine the same are through the following error messages on your switch logs

i) %STANDBY-3-DUPADDR: Duplicate address

ii) %MAC_MOVE-SP-4-NOTIF: Host   ---> Between Hosts

iii) High CPU on the devices

All the above state that there is a loop in your network and STP was not able to take action on the same.

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