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C H A P T E R 8 Forwarding Database (FDB)
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Permanent Entries
All entries entered through the command line interface are stored as
permanent.Only entries designated as Permanent are retained in the
database if the switch is reset or a power off/on cycle occurs. A
permanent entry can either be a unicast or multicast MAC address.
The switch can support up
to 256 permanent MAC
entries in the forwarding
database.
Once created, permanent entries cannot be updated. For example,
the permanent entry store is not updated when any of the following
take place:
• A VLAN is deleted.
• A VLANid is changed.
• A port mode is changed (tagged/untagged).
• A port is deleted from a VLAN.
• A port is disabled.
• A port enters a blocking state.
• A port QoS setting is changed.
• A port goes down (link down).
Blackhole Entries
A blackhole entry configures the 480T routing switch to discard
packets with a specified MAC destination address.
Blackhole entries are useful as a security measure or in special
circumstances where a specific destination address must be
discarded.
Blackhole entries are treated like permanent entries in the event of
a switch reset or power off/on cycle.
Blackhole entries are never aged out of the database.
How FDB Entries Get Added
Add entries to the FDB in two ways:
• The switch can learn entries by updating its FDB with the source
MAC address from a packet, the VLAN, and the port identifier
where the source packet was received.