Allied Telesis Rapier Switch - Manual (Page 48)

48 Rapier Switch Software Reference
Software Release 2.5.1
C613-02025-00 REV B
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,
the switch floods the frame on all ports in the VLAN except the port on which
the frame was received. If the destination address is found, the switch discards
the frame if the port is not in the STP ‘Forwarding’ state, if the destination
address is on the same port as the source address, or if there is a static filter
entry for the destination address set to DISCARD (“Layer 2 Filtering” on
page 49). Otherwise, the frame is forwarded on the indicated port.
This whole process can further be modified by the action of static switch filters.
These are configurable filters which allow switched frames to be checked
against a number of entries.
The Forwarding Process provides storage for queued frames to be transmitted
over a particular port or ports. More than one transmission queue may be
provided for a given port. Which transmission queue a frame is sent to is
determined by the user priority tag in the Ethernet frame, and the Quality of
Service mapping.