Cabletron Systems NB30 manual Filtering Database, Changing Port Priority, Changing Path Cost

NB-30 Bridging

Changing Port Priority

To change the part of the Port Priority used in priority comparisons:

1.Highlight the port Priority field for the desired port, and enter the new priority identifier. Only valid hexadecimal numbers (0 to FF) are allowed in this field. The default is 80 hexadecimal.

2.Click on Set. The new port priority will be saved.

Changing Path Cost

To change the Path Cost:

1.Highlight the Path Cost field for the desired port, and type in a new value from 1 to 65535 decimal (default is 100 decimal).

2.Click on Set.

The new path cost will be applied to the port.

Filtering Database

The Filtering Database, which makes up the IEEE 802.1d Source Address Table, is used to determine which frames will be forwarded across the bridge from one network segment to another.

Transparent bridges like the NB-30 use the Filtering Database to determine a packetÕs route through the bridge. During initialization, the bridge copies the contents of its Permanent Database to the Filtering Database. Next, the bridge learns network addresses by entering the source address and port association of each received packet into the Filtering Database. When in the Forwarding state, the bridge examines each received packet, and then compares the destination address to the contents of the Filtering Database. If the destination address is located on the network from which the packet was received, the bridge Þlters (does not forward) the packet. If the destination address is located on a different network, the bridge forwards the packet to the appropriate network. If the destination address is not found in the Filtering Database, the bridge forwards the packet to all networks. To keep Filtering Database entries current, older entries are purged after a period of time, which is called the Dynamic Ageing Time.

The NB-30 Filtering Database consists of two separate databases: the Static and the LearnedDatabases.

The Static Database contains addresses that are entered by a network administrator. You add these addresses directly to the database while the bridge is powered up, or to the deviceÕs battery-backed RAM so that they are stored on shutdown until the next power-up.

The Learned Database consists of addresses that accumulate as part of the bridgeÕs learning process as it is up and running. These do not remain in the Source Address Table when the system is shut down. The Learned Database also contains the addresses that are in the Static Database upon start-up of the bridge.

3-24 Filtering Database