The Learning Process - Allied Telesis SwitchBlade x908 Series Software Reference Manual

Switching Introduction
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.

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
command, and re-enabled using the
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. It can be disabled with the
ageing-time
page
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 setting the mac address-table ageing-time is 300 seconds (5 minutes) and can
be modified by using the command
To set the mac address-table ageing-time to 1000 seconds
awplus#configure terminal
awplus(config)#mac address-table
ageing-time 1000
To display general switch settings, including settings for switch learning and the switch ageing
timer, use the
14.8
command. You can enable it with the
15.12.
show system command on page
Software Reference for SwitchBlade® x908, x900 and x600 Series Switches
TM
AlliedWare Plus Operating System - Software Version 5.3.1
mac address-table acquire command on page
mac address-table ageing-time command on
mac address-table ageing-time.
Enter the config terminal mode
Set the ageing time to 1000 seconds
8.30.
no mac address-table acquire
15.11.
no mac address-table
C613-50007-01 REV B