Cabletron Systems 9A128-01 manual Filtering Database, Changing Path Cost

Bridging

Changing Path Cost

To change the Path Cost:

1.If necessary, select the desired port by clicking the mouse to highlight the port in the lower right quadrant of the window. The lower left quadrant of the window will now allow you to edit parameters for the selected port.

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

3.Click on Set.

The new path cost will be applied to the port.

Filtering Database

The Filtering Database, which makes up the IEEE 802.1 Source Address Table, is used to determine which frames will be forwarded or filtered between the selected module’s bridging ports.

Transparent bridges like the 9A128-01 use the Filtering Database to determine a packet’s 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 checks it against the contents of the Filtering Database. If the destination address is located on the network from which the packet was received, the bridge filters (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 Filtering Database consists of two separate databases: the Static and the

Learned Databases.

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 selected module’s battery-backed RAM so that they are stored on shutdown till the next power-up.

The Learned Database consists of addresses that accumulate as part of the bridge’s 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.

Entries to the Source Address Table are one of four types: Permanent, Static,

Dynamic, or Learned.

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