3com 9000 SX Manual De Usuario

This chapter describes the contents of the Switch forwarding database 
(FDB), how the FDB works, and how to configure the FDB.

The Switch 9000 maintains a database of all addresses received on all 
of its ports. It uses the information in this database to decide whether 
a frame should be forwarded or filtered. 

The database holds up to a maximum of 12,000 entries. Each entry 
consists of the MAC address of the device, an identifier for the port on 
which it was received, and an identifier for the VLAN to which the 
device belongs. Frames destined for devices that are not in the FDB are 
flooded to all members of the VLAN.

The following are three types of entries in the FDB:

■

Dynamic entries — Initially, all entries in the database are dynamic. 
Entries in the database are removed (aged-out) if, after a period of 
time (ageing time), the Switch has not received a frame containing 
that source address. This prevents the database from becoming full 
with obsolete entries by ensuring that when a device is removed 
from the network, its entry is deleted from the database. Dynamic 
entries are deleted from the database if the Switch is reset or a 
power off/on cycle occurs. 

For more information about setting the Ageing time, refer to 
“Configuring FDB Entries,” page 6-3.

■

 entries — If the ageing time is set to 00:00, all dynamic 

entries in the database are defined as non-ageing entries. This 
means that they do not age, but they are still deleted if the Switch 
is reset.

SW9000.BK  Page 1  Wednesday, April 1, 1998  11:00 AM