3Com 3800 - Manual (Page 95)

6
S
WITCH
F
ORWARDING
D
ATABASE
(FDB)
This chapter describes the contents of the Switch forwarding database
(FDB), how the FDB works, and how to configure the FDB.
Overview of the
FDB
The Switch 3800 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.
FDB Contents 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.
FDB Entry Types 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.
■
Static 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.
SW3800.BK Page 1 Tuesday, May 5, 1998 5:20 PM