Allied Telesis Rapier Switch - Manual (Page 47)

Layer 2 Switching 47
Software Release 2.5.1
C613-02025-00 REV B
ACCEPTABLE parameter can only be set if the port is untagged for one VLAN.
In this case, the default is ALL, admitting all tagged and untagged frames. If
the port is tagged for all the VLANs to which it belongs, the ACCEPTABLE
parameter is automatically set to VLAN, and cannot be changed to admit
untagged frames.
The INFILTERING parameter enables or disables Ingress Filtering of frames
admitted according to the ACCEPTABLE parameter, on the specified ports.
Each port on the switch belongs to one or more VLANs. If INFILTERING is set
to ON, Ingress Filtering is enabled: any frame received on a specified port is
only admitted if the port belongs to the VLAN with which the frame is
associated. Conversely, any frame received on the port is discarded if the port
does not belong to the VLAN with which the frame is associated. Untagged
frames admitted by the ACCEPTABLE parameter are admitted, since they have
the numerical VLAN Identifier (VID) of the VLAN for which the port in an
untagged member. If OFF is specified, Ingress Filtering is disabled, and no
frames are discarded by this part of the Ingress Rules. The default setting is
OFF.
To display the current Ingress Rules, use the command:
SHOW SWITCH PORT=port-list
The Learning Process
The Learning Process uses an adaptive learning algorithm, sometimes called
backward learning, to discover the location of each station on the extended LAN.
All frames admitted by the Ingress Rules on any port are passed on to the
Forwarding Process if they are for destinations within the same VLAN. Frames
destined for other VLANs are passed to the layer three protocol, for instance IP.
For every frame admitted, the frame’s source MAC address and numerical
VLAN Identifier (VID) are compared with entries in the Forwarding Database
for the VLAN (also known as a MAC address table, or a forwarding table)
maintained by the switch. The Forwarding Database contains one entry for
every unique station MAC address the switch knows in each VLAN.
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