switchport mac-address

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Jul 19th, 2010
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When a switch has a mac address , and our pc is connected to the switch, the pc arp cache contains the mac of the switch and not the mac of the port to which it is connected. On the switch if we go to interface mode((config)# interface fastethernet 0/x )where x, is the port number, we find a mac address there. What is it used for?

  Can some one help plz

Thank you

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milan.kulik Tue, 07/20/2010 - 02:05
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don't forget the PC arp cache contains only MAC addresses which are related to IP addresses of hosts within the same subnet.

So as the switch is using a virtual L3 interface (int VLANx) for his management address, it also uses a virtual MAC address, not the port MAC address.

IMHO, if you configure a switch port as a routed one and connect your PC to that port, you should see the port MAC address with the port IP address in the PC ARP cache.

The port MAC address might be also used for L2 frames generated by the switch from the port - frames used for trunk and Etherchannel negotiation, VTP, CDP, etc. I'm not 100% sure though, some of them might be using virtual MAC addresses or some modified ones (like STP does).




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