Specifications

104 ExtremeWare XOS 11.0 Concepts Guide
Forwarding Database
FDB Entry Types
FDB entries may be dynamic or static, and the entries 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. This entry 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—that is, a dynamic entry is removed from the FDB (aged-out) if
the device does not transmit for a specified period of time (the aging time). This aging process
prevents the FDB 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 105.
• Static entries—A static entry does not age and does not get updated through the learning process. A
static entry 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 CLI 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.
Non-permanent static entries are created by the switch software for various reasons, typically upon
switch boot-up. These entries are identified by the “s” flag in
show fdb output.
If the FDB entry aging time is set to zero, all entries in the database are considered static, non-aging
entries. This means that the entries do not age, but they are still deleted if the switch is reset.