Extreme Networks ExtremeWare 7.3.0, Command Reference Manual

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ExtremeWare Software 7.3.0 Command Reference Guide 353
6
FDB Commands
This chapter describes commands for:
• Configuring FDB entries
• Displaying FDB entries
• Configuring and enabling FDB scanning
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.
Each FDB entry consists of the MAC address of the device, an identifier for the port on which it was
received, and an identifier for the VLAN to which the device belongs. Frames destined for devices that
are not in the FDB are flooded to all members of the VLAN.
The FDB has four types of entries:
• Dynamic entries —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 of 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 switch is reset or a power off/on cycle occurs.
• Nonaging entries —If the aging time is set to zero, all aging entries in the database are defined as
static, nonaging 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 create permanent entries. A permanent entry can
either be a unicast or multicast MAC address. All entries entered through the command line
interface (CLI) are stored as permanent.
• Blackhole entries —A blackhole entry configures the switch to discard packets with a specified MAC
destination address. 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 CLI.
A QoS profile can be associated with a MAC address (and VLAN) of a device that will be dynamically
learned. The FDB treats the entry like a dynamic entry (it is learned, it can be aged out of the database,
and so on). The switch applies the QoS profile as soon as the FDB entry is learned.