Single forwarding database operation

When a packet arrives with a destination MAC address that matches a MAC address in the switch's forwarding table, the switch tries to send the packet to the port listed for that MAC address. But if the destination port is in a different VLAN than the VLAN on which the packet was received, the switch drops the packet. This is not a problem for a switch with a multiple forwarding database because the switch allows multiple instances of a given MAC address, one for each valid destination. However, a switch with a single forwarding database allows only one instance of a given MAC address.


If you connect both switch types through multiple ports or trunks belonging to different VLANs and enable routing on the switch with the multiple-forwarding database, then the port and VLAN record maintained on the switch with the single-forwarding database for the multiple-forwarding database can change frequently. This may cause poor performance and the appearance of an intermittent or broken connection.