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Overview of the FDB
How FDB Entries
Get Added
5-2
Non-aging entries — If the aging time is set to zero, all aging
entries in the database are defined as static, non-aging entries.
This means that they do not age, but they are still deleted if
the switch is reset.
Permanent entries — Permanent entries are retained in the
database if the switch is reset or a power off/on cycle occurs.
The system administrator must make entries permanent. A
permanent entry can either be a unicast or multicast MAC
address. All entries entered by way of the command-line
interface are stored as permanent. The switch can support a
maximum of 64 permanent entries.
Once created, permanent entries stay the same as when they were
created. 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 blocking state.
— A port QoS setting is changed.
— A port goes down (link down).
Blackhole entries — A blackhole entry configures packets
with a specified MAC destination address to be discarded.
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.
Entries are added into the FDB in the following two ways:
The switch can learn entries. 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.
You can enter and update entries using a MIB browser, an
SNMP Network Manager, or the command-line interface (CLI).
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