HP 6120XG HP ProCurve Series 6120 Blade Switches Advanced Traffic Management G - Page 45
Multiple VLAN Considerations, Single Forwarding Database Operation
View all HP 6120XG manuals
Add to My Manuals
Save this manual to your list of manuals |
Page 45 highlights
Static Virtual LANs (VLANs) Multiple VLAN Considerations Multiple VLAN Considerations Switches use a forwarding database to maintain awareness of which external devices are located on which VLANs. Some switches, such as the switches covered in this guide, have a multiple forwarding database, which means the switch allows multiple database entries of the same MAC address, with each entry showing the (different) source VLAN and source port. Other switch models have a single forwarding database, which means they allow only one database entry of a unique MAC address, along with the source VLAN and source port on which it is found. All VLANs on a switch use the same MAC address. Thus, connecting a multiple forwarding database switch to a single forwarding database switch where multiple VLANs exist imposes some cabling and port VLAN assignment restrictions. Table 2-4 illustrates the functional difference between the two database types. Table 2-4. Example of Forwarding Database Content Multiple Forwarding Database MAC Address Destination Destination VLAN ID Port 0004ea-84d9f4 1 A5 0004ea-84d9f4 22 A12 0004ea-84d9f4 44 A20 0060b0-880a81 33 A20 This database allows multiple destinations for the same MAC address. If the switch detects a new destination for an existing MAC entry, it just adds a new instance of that MAC to the table. Single Forwarding Database MAC Address Destination Destination VLAN ID Port 0004ea-84d9f4 100 A9 0060b0-880af9 105 A10 0060b0-880a81 107 A17 This database allows only one destination for a MAC address. If the switch detects a new destination for an existing MAC entry, it replaces the existing MAC instance with a new instance showing the new destination. 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 2-17