S
UMMIT
S
WITCH
I
NSTALLATION
AND
U
SER
G
UIDE
6-1
6
Switch Forwarding Database
(FDB)
This chapter describes contents of the the Switch forwarding database (FDB), how the
FDB works, and how to conÞgure the FDB.
O
VERVIEW
OF
THE
FDB
The Summit maintains a database of all media access control (MAC) addresses received
on all of its ports. It uses the information in this database to decide whether a frame
should be forwarded or Þltered.
FDB C
ONTENTS
The database holds up to a maximum of 128K entries. Each entry consists of the MAC
address of the device, an identiÞer for the port on which it was received, and an
identiÞer for the VLAN to which the device belongs. Frames destined for devices that
are not in the FDB are ßooded to all members of the VLAN.
FDB E
NTRY
T
YPES
The following are three types of entries in the FDB:
¥ Dynamic entries
Ñ Initially, all entries in the database are dynamic. Entries in the
database are removed (aged-out) if, after a period of time (aging time), the device
has not transmitted. 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
SUMMIT.BK Page 1 Thursday, September 25, 1997 12:33 PM
