Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 350)

Switching Introduction
Software Reference for x310 Series Switches
14.8 AlliedWare Plus TM Operating System - Version 5.4.4C C613-50046-01 REV A
Access Mode
This mode can be used to connect to VLAN unaware devices. Frames to and from access
mode ports carry no VLAN tagging information.
Trunk Mode
This mode is used to connect VLAN capable devices. All devices that connect using trunk
mode ports must be VLAN aware.
You can specify a “native” VLAN on a trunk port. When the port receives untagged packets,
it will tag the packets with the VID of the native VLAN. Note that packets from the native
VLAN egress the port untagged.
To specify the native VLAN, use the switchport trunk native vlan command on page
17.27 command.
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 when they are for destinations in the same VLAN. Frames destined for other
VLANs are passed to a Layer 3 protocol, such as IP. For every frame admitted, the frame’s
source MAC address and VID are compared with entries in the forwarding database for the
VLAN (also known as a MAC Address table) maintained by the switch. When the frame’s
source address is not in the forwarding database for the VLAN, the address is added and
an ageing timer for that entry is started. When 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. It can be disabled with the no mac address-table
acquire command, and re-enabled using the mac address-table acquire command on
page 15.17 .
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 with information about
stations that are inactive or have been disconnected from the network. It also ensures that
entries for active stations are kept alive in the forwarding database.
By default, the ageing timer is enabled with a default ageing-time. The ageing timer can
be reset to the default with the
no mac address-table ageing-time command. The
ageing timer can be increased or decreased using the mac address-table ageing-time
command.
If switch learning is disabled and the ageing timer has aged out all dynamically learned
filter entries, only statically entered MAC source addresses decide the packets to forward
or discard. When the switch finds no matching entries in the forwarding database during
the forwarding process, all switch ports in the VLAN are flooded with the packet, except
the port that received it.
The default for the mac address-table ageing-time is 300 seconds (5 minutes) and can be
modified by using the command
mac address-table ageing-time . The no mac address-
table ageing-time command will reset the ageing-time back to the default (5 minutes).