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same mac in a switch

We have some computer,they're mac address decide by software.Now we find some same mac's computer in a switch.The same mac's computer belong to different vlan. Why the same mac's computer work well? The switch is Catalyst 2950:

show mac-add

Mac Address Table

------------------------------------------

Vlan Mac Address Type Ports

---- ----------- ---- -----

160 00e0.fc00.1405 DYNAMIC Fa0/3

160 00e0.fc00.1409 DYNAMIC Fa0/4

160 00e0.fc00.1505 DYNAMIC Fa0/1

160 00e0.fc00.1509 DYNAMIC Fa0/2

220 00e0.fc00.1405 DYNAMIC Fa0/13

220 00e0.fc00.1409 DYNAMIC Fa0/14

220 00e0.fc00.1505 DYNAMIC Fa0/15

220 00e0.fc00.1509 DYNAMIC Fa0/16

1 REPLY
Bronze

Re: same mac in a switch

It works well because the duplicate addresses are in different vlans, so the vlan-address pair is unique.

If a frame arrives in vlan 160 with a destination of 00e0.fc00.1405, the switch looks up the vlan-address pair in its Mac Address Table and finds that it needs to forward the frame out Fa0/3.

Similarly if a frame arrives in vlan 220 the table lookup results in the frame being sent out Fa0/13.

hth

Herbert

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