Perle Systems P840 User Manual download pdf (Page 10)

Introduction

Address Purging

To achieve this routine housekeeping, the filter table contains the LAN addresses, along with their LAN port

identifier, and a timer flag. Each time a particular address is looked up or added to the table, a timer flag is set for

the “fresh” entry. When a time interval, defined by the Bridge/Router Manager expires, the address table is scanned

and any “stale” entries that have not been used since the timer expired are removed. This timer is called the “aging

timer” and may be controlled through the bridge options.

Purging the address does not prevent the station from using the bridging facilities, since the location of the station

may be re-learned. However, there must be a balance, since a small aging timer value will mean that the bridge must

learn many addresses often. This also has an effect on performance.

Aging Exception

“Permanent” address entries are an exception to the aging rule. A permanent address is one that is not subject to the

aging timer and will remain in the filter table for an indefinite period of time.

A table is reserved for permanent address entries, separate from the table that is used for those non-permanent entries

that are subject to aging. These tables may be displayed and modified with the bridge/router options discussed in

this manual. Access is made locally from each Bridge/Router Console or one bridge/router can be made Master,

able to control all functions of a partner P840 router.

Filled Address Table

Sometimes filter address table may become full. (The filter table can hold 2048 address entries.) A procedure is automatically

followed in this event.

This procedure defines that the address, if it does not exist in the table, will not be added, and will be treated as any other

unknown address. In this case the frame will be passed to the other segment. An alarm will also be generated with the

message “Station Address Table Full,” and from this point, another alarm will be generated only if in the meantime the table

empties by 1/3 and then fills up again.

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Perle Systems P840 User Manual Page 10