82 AT-8800 Series Switch User Guide
Software Release 2.6.1
C613-02039-00 REV A
If the frame’s source address is not already in the Forwarding Database for the
VLAN, the address is added and an ageing timer for that entry is started. If the
frame’s source address is already in the Forwarding Database, the ageing timer
for that entry is restarted. By default, switch learning is enabled, and it can be
disabled or enabled using the commands:
DISABLE SWITCH LEARNING
ENABLE SWITCH LEARNING
If the ageing timer for an entry in the Forwarding Database expires before
another frame with the same source address is received, the entry is removed
from the Forwarding Database. This prevents the Forwarding Database from
being filled up with information about stations that are inactive or have been
disconnected from the network, while ensuring that entries for active stations
are kept alive in the Forwarding Database. By default, the ageing timer is
enabled, and it can be disabled or enabled using the commands:
ENABLE SWITCH AGEINGTIMER
DISABLE SWITCH AGEINGTIMER
If switch learning is disabled and the ageing timer has aged out all dynamically learned
filter entries, only statically entered MAC source addresses will be used to decide which
packets to forward or discard. If the switch finds no matching entries in the Forwarding
Database during the Forwarding Process, then all switch ports in the VLAN will be
flooded with the packet, except the port on which the packet was received.
The default value of the ageing timer is 300 seconds (5 minutes), and this can
be modified using the command:
SET SWITCH AGEINGTIMER=10..1000000
The Forwarding Database relates a station’s (source) address to a port on the
switch, and is used by the switch to determine from which port (if any) to
transmit frames with a destination MAC address matching the entry in the
station map.
To display the contents of the Forwarding Database, use the command:
SHOW SWITCH FDB [ADDRESS=macadd]
[DISCARD={SOURCE|DESTINATION}] [HIT={YES|NO}]
[L3={YES|NO}] [PORT={portlist|ALL}]
[STATUS={STATIC|DYNAMIC}] [VLAN={vlanname|1..4094}]
To display general switch settings, including settings for switch learning and
the switch aging timer, use the command:
SHOW SWITCH
The Forwarding Process
The Forwarding Process forwards received frames that are to be relayed to
other ports in the same VLAN, filtering out frames on the basis of information
contained in the station map and on the state of the ports. If a frame is received
on the port for a destination in a different VLAN, it is either Layer 3 switched if
it is an IP packet, or looked up in the Layer 3 routing tables (see the Rapier
Switch Software Reference.)
Forwarding occurs only if the port on which the frame was received is in the
Spanning Tree ‘Forwarding’ state. The destination address is then looked up in
the Forwarding Database for the VLAN. If the destination address is not found,