MAC address table for each VLAN

Sep 29, 2010 2 Replies
M

Hello,



some L2 switches have separate MAC address tables for VLANs, others don't and share the global one. Then for the latter case packets between two VLANs are forwarded, as long as there are entries in MAC table.



For example:



port1 in VLAN1: station1 with MAC1 port2 in VLAN2: station2 with MAC2



And the table looks as follows:



port1 MAC1 AgeingTime1 port2 MAC2 AgeingTime2



With such configuration any packet from stattion1 towards station2 is forwarded by the switch via port2. Doesn't this break the VLAN concept (i.e. communication between VLANs is possible only via router)?



Please help me to understand this. Thanks !


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A

I'm not sure I understand why the tables you show imply that frames from host 1 would be switched directly to host 2, at layer 2.

The MAC addresses will be aged out, just as they are in any "learning bridge," but the VLAN association is with the switch port, in this case. Not with any one MAC address. For example, any new MAC address appearing at Port 1 will become associated with VLAN 1.

Host 1 should not be able to communicate directly with host 2, unless someone introduces a router with access to both VLANs.

Bert

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M

Bonjour Mark,

In your first table MAC1 is a source address, in your second table MAC1 is a destination address. Why don't you have the VLAN information in the forwarding table?

Best regards, Michelot

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