Extreme Networks ExtremeWare XOS 10.1, Manual

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ExtremeWare XOS 10.1 Concepts Guide 75
6
Forwarding Database (FDB)
This chapter describes the following topics:
• Overview of the FDB on page 75
• FDB Configuration Examples on page 77
• MAC-Based Security on page 78
•
Displaying FDB Entries on page 78
Overview of the FDB
The switch 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 filtered.
FDB Contents
Each FDB entry consists of the MAC address of the device, an identifier for the port and VLAN on
which it was received, and the age of the entry. Frames destined for MAC addresses that are not in the
FDB are flooded to all members of the VLAN.
How FDB Entries Get Added
Entries are added into the FDB in the following ways:
• The switch can learn entries by examining packets it receives. The system updates its FDB with the
source MAC address from a packet, the VLAN, and the port identifier on which the source packet is
received.
The ability to learn MAC addresses can be enabled or disabled on a port-by-port basis. You can also
limit the number of addresses that can be learned, or you can “lock down” the current entries and
prevent additional MAC address learning.
• You can enter and update entries using the command line interface (CLI).
• Certain static entries are added by the system upon switch boot up.