Extreme Networks ExtremeWare XOS 10.1, Manual

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76 ExtremeWare XOS 10.1 Concepts Guide
Forwarding Database (FDB)
FDB Entry Types
FDB entries may be dynamic or static, and may be permanent or non-permanent. The following
describes the types of entries that can exist in the FDB:
• Dynamic entries
—A dynamic entry is learned by the switch by examining packets to determine the
source MAC address, VLAN, and port information. The switch then creates or updates an FDB entry
for that MAC address. Initially, all entries in the database are dynamic, except for certain entries
created by the switch at boot up.
Dynamic entries are flushed and relearned (updated) when any of the following take place:
—
A VLAN is deleted.
— A VLAN identifier (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 goes down (link down).
A non-permanent dynamic entry is initially created when the switch identifies a new source MAC
address that does not yet have an entry in the FDB. The entry may then be updated as the switch
continues to encounter the address in the packets it examines. These entries are identified by the “d”
flag in
show fdb
output.
A permanent dynamic entry is created by command through the CLI, but may then be updated as the
switch encounters the MAC address in the packets that it examines. A permanent dynamic entry is
typically used to associate QoS profiles with the FDB entry. Permanent dynamic entries are identified
by the “p” and “d” flags in
show fdb
output.
Both types of dynamic entries age—a dynamic entry will be removed from the FDB (aged-out) if the
device does not transmit for a specified period of time (the aging time). This prevents the database
from becoming full with obsolete entries by ensuring that when a device is removed from the
network, its entry is deleted from the database. The aging time is configurable. For more information
about setting the aging time, see “Configuring the FDB Aging Time” on page 78.
• Static entries
—A static entry does not age, and does not get updated through the learning process. It
is maintained exactly as it was created. Conditions that cause dynamic entries to be updated, such as
VLAN or port configuration changes, do not affect static entries.
If the same MAC address is detected on another virtual port that is not defined in the static FDB
entry for the MAC address, it is handled as a blackhole entry.
A permanent static entry is created through the command line interface, and can be used to associate
QoS profiles with a non-aging FDB entry. Permanent static entries are identified by the “s” and “p”
flags in
show fdb
output.