A question about cam-table in catalyst-switch

[zhengzhe_bj]

All we are aware that there is a cam-table in catalyst-switch,binding the specific port.sn and the hosts' MAC,BUT

1.HOW the switch work when two or more hosts(with the same MAC) connect to a hub and then make a single connection between the hub and the switch?
2.HOW the switch work when two or more hosts(with the same MAC) connect to the different physical-ports of the switch?


thank you!

[Conwyn]

Hi Zhengzhe

Two computers should not have the same mac address. The mac address = manufacture (24 bits) + unique number for manufacturer (24 bits)
You can set the mac address known as local admin address but that was mainly used before IP world to simplify bridging.
Two PCs connected to hub will create two seperate entries in the CAM. If you move the device to another hub the old entry is deleted.
If two PC had the same mac there would be only one entry and the traffic would be sent to the hub which would send to both PCs


Regards Conwyn

[Angela]

I agree with Conwyn's explanation, but I would like to elaborate a little:

If it is possible (someone altered the MAC address of the machines) to have the same MAC address,
the hub will process the frames (if both devices are connected to only hub, no switch is involved) as usual since hub doesn't need to know MAC address to perform its job. The frame is broadcasted to every port except the incoming port.
On the other hand, if 2 devices (with the same MAC address) are connected to a switch, the switch would be confused over WHERE to send the packet since there are 2 destinations.

Some hackers use the technic of changing MAC address to receive data that is suppose to send to the original recipient. This security risk is known as MAC address spoofing.


Regards,
Angela