Allied Telesis AR450S Manuel d'utilisateur télécharger pdf (Page 14)

3-14 AR400 Series Router Software Reference

Software Release 2.6.6

C613-03079-00 REV A

The default settings for the Ingress Rules are to Admit All Frames, and for

Ingress Filtering to be OFF. This means that if no VLAN configuration has been

done, all incoming frames pass on to the Learning Process, regardless of

whether they are VLAN tagged. The parameters for each port’s Ingress Rules

can be configured using the command:

SET SWITCH PORT={port-list|ALL} [INFILTERING={ON|OFF}]

[other-options...]

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 is compared with

entries in the Forwarding Database (also known as a MAC address table, or a

forwarding table) maintained by the router. The Forwarding Database contains

one entry for every unique station MAC address the router knows in each

VLAN.

If the frame’s source address is not already in the Forwarding Database, 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.

To disable or enable the ageing timer, use 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 are used to decide which

packets to forward or discard. If the router finds no matching entries in the Forwarding

Database during the Forwarding Process, then all switch ports in the VLAN are flooded

with the packet, except the port the packet was received on.

The default of the ageing timer is 304 seconds (approximately 5 minutes). To

modify the default, use the command:

SET SWITCH AGEINGTIMER=16..4080

The Forwarding Database relates a station’s (source) address to a port on the

router, and is used by the router to determine from which port (if any) to

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Allied Telesis AR450S Manuel d'utilisateur Page 14

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