Switch Interface Mac Address

[Suprit Chinchodikar]

Let's say we have got pure layer 2 switch, for example cisco old model 2960 switch. The ports on this switch model does not support routing mode. So, in this case whey every ports of this switch have got their own mac address? What is the purpose of that mac address?

Also, for STP bpdu communication this switch uses its system mac address.

Thanks,
Suprit

[Richard Burts]

As part of the implementation of the Ethernet protocol every Ethernet needs a mac address.

Can you check perhaps a CDP frame sent by the switch and tell us what is the source mac?

[Suprit Chinchodikar]

Hello Rick,
Need to simulate the CDP in my lab, but i'm afraid I dont have 2960 switch, so will be doing what image I have with me.

Thanks,

Suprit

[Suprit Chinchodikar]

Hello @Richard Burts,
I just tried to capture the CDP frame and found that the source mac is the interface mac of the switch.

[MHM Cisco World]

....

[Suprit Chinchodikar]

Hello @MHM Cisco World ,
What layer 2 protocols are you talking about over here? STP, ARP, Layer2 port channel?
STP uses the system mac address and for arp it uses the host mac address to fill up its CAM table.

[MHM Cisco World]

...

[Suprit Chinchodikar]

Still, the two mac address that would be in Layer 2 frame source mac (host initiating the ARP) and destination will be all F's.
and the mac in the ARP packet will have target mac of the host initiating the ARP and the destination MAC will be all 0's.
So, my question still remains the same, why we need mac on interface or a pure layer 2 switch?

[MHM Cisco World]

as you like.

[Joseph W. Doherty]

" So, in this case whey every ports of this switch have got their own mac address? What is the purpose of that mac address?"

It's possible, there is no actual purpose.  However, just as I recall when some of the 2960 series, suddenly, supported some basic routing, purpose might have been for future product enhancement.

Or, when manufacturing products, one important method to keeping production costs down, is using "common" components, whenever possible.  For example, (and I don't know if this is the case) perhaps the 2960/3560/3750 series use many base/identical components.  I.e. interface MACs, on a L2 switch that has no real need for them, just might be a hardware "artifact" because other more "featured" models need that function.