HP 2610, Advanced Traffic Management Manual

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Static Virtual LANs (VLANs)
Port-Based Virtual LANs (Static VLANs)
Series 2600/2600-PWR switches
Multiple-Forwarding Databases* Single-Forwarding Database*
Series 2510 switches
*To determine whether other vendors’ devices use single-forwarding
or multiple-forwarding database architectures, refer to the
documentation provided for those devices.
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 (refer to table 2-7, above) 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 (1) you connect the two types of switches through multiple
ports or trunks belonging to different VLANs, and (2) enable routing on the
switch having the multiple-forwarding database; then, on the switch having
the single-forwarding database, the port and VLAN record it maintains for the
connected multiple-forwarding-database switch can frequently change. This
causes poor performance and the appearance of an intermittent or broken
connection.
Example of an Unsupported Configuration and How
to Correct It
The Problem. In figure 2-8, the MAC address table for Switch 8000M will
sometimes record the multiple-forwarding database switch as accessed on
port A1 (VLAN 1), and other times as accessed on port B1 (VLAN 2):
2-12