User guide

7-2 E
XTREME
W
ARE
S
OFTWARE
U
SER
G
UIDE
F
ORWARDING
D
ATABASE
(FDB)
FDB E
NTRY
T
YPES
The following are four types of entries in the FDB:
• 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 with 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. For more information about setting
the aging time, refer to the section “Configuring FDB Entries,” later in this chapter.
• 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 Summit switch can support a maximum of 64 permanent entries, the
BlackDiamond switch supports a maximum of 254 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 the 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.