Chapter 10: Forwarding Database; Overview Of The Fdb; Fdb Contents; How Fdb Entries Get Added - Extreme Networks ExtremeWare XOS Guide Manual

10 Forwarding Database
This chapter describes the following topics:
Overview of the FDB on page 175
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FDB Configuration Examples on page 177
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Configuring the FDB Aging Time on page 177
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MAC-Based Security on page 178
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Displaying FDB Entries on page 178
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Overview of the FDB

The switch maintains a database of all 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 Forwarding Database (FDB) entry consists of:
The MAC address of the device
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An identifier for the port and VLAN on which it was received
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The age of the entry
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The number of IP FDB entries that use this MAC address as a next hop or last hop
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Flags
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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
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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.
NOTE
For more information on port control for learning MAC address, refer to
ExtremeWare XOS 11.1 Concepts Guide
Chapter 5.
175