Interface Mac Addresses

Posted on 2011-09-03
Last Modified: 2012-05-12
Can someone tell me why show interface command shows 2 mac addresses.Even though they are the same.?

Hardware is EtherChannel, address is 0016.47d3.ed8c (bia 0016.47d3.ed8c)

Question by:jskfan
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LVL 46

Expert Comment

by:Craig Beck
ID: 36480011
An interface can have a software-configured MAC address.  This is displayed when you use the show interface command.  The MAC address in brackets (bia 0016.47d3.ed8c) is the burned-in MAC address - the hardware-set value.

Author Comment

ID: 36480081
the Burned in MAC is what the manufacturer print on the Network Adapter Card.
Where does the software-configured MAC address come from ?
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Expert Comment

by:Craig Beck
ID: 36480086
It could come from HSRP, bridge configuration, or any number of other features depending on configuration.
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LVL 46

Expert Comment

by:Craig Beck
ID: 36480088
.... if the software MAC and burned-in MAC both match it means that the interface is using the burned-in MAC.

Author Comment

ID: 36480464
I happened to see this on the switch, there is no HSRP configured
LVL 46

Accepted Solution

Craig Beck earned 250 total points
ID: 36480560
Ok, I think you misunderstood me...

The interface on the switch shows the 'configured' MAC address (The MAC address currently attached to that interface), and the Hardware MAC address.
If the MAC address has not been 'configured' the switch will still show the MAC address which is in use on that interface AND the hardware MAC address, as set by the device manufacturer.
LVL 22

Expert Comment

ID: 36480619
Can you post the config for the port?
LVL 17

Assisted Solution

MAG03 earned 250 total points
ID: 36480735
There will always be a software mac address (configurable) and a hardware mac address (non-configurable) because both the software and hardware require that they have it. By default the software mac address will use the hardware mac address because none have been hardcoded. If you change the software mac address by use of the interface command mac-address aaaa.aaaa.aaaa, for example, the output of the show interface command will look something like this:
Hardware is Fast Ethernet, address is aaaa.aaaa.aaaa (bia c205.2648.f100)

Author Closing Comment

ID: 36482595
good explanation guys!

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