3 - i, Mac address filtering, Ntroduction to – Black Box LR1530A-EU-R3 User Manual

Page 63: Iltering

3 - I

NTRODUCTION TO

ILTERING

The router provides programmable filtering which gives you the ability

to control under what conditions Ethernet frames are forwarded to

remote networks. There are many reasons why this might need to be

accomplished, some of which are security, protocol discrimination,

bandwidth conservation, and general restrictions.
Filtering may be accomplished by using two different methods. The

first method is to filter or forward frames based solely on their source

or destination MAC address. This method of filtering is useful when

bridging between LANs and for providing remote access security in

any type of network. The Ethernet MAC (Media Access Control)

address is checked against the addresses in the filtering list and the

frame is filtered or forwarded accordingly.
The second method of filtering is pattern filtering where each frame is

checked against a filter pattern. The filter pattern may be defined to

perform a check of any portion of the Ethernet frame. Separate filter

patterns may be defined for bridged frames, IP routed frames, and IPX

routed frames.
For more information on filtering, please refer to the Programmable

Filtering section of the router reference manual file. The PDF file is

located on the accompanying CD-ROM.

MAC Address Filtering

MAC address filtering is provided by three built-in functions.
The first function is “Filter if Source”; the second is “Filter if

Destination.” The third function allows you to change the filter

operation from “positive” to “negative.” The positive filter operation

causes frames with the specified MAC addresses to be filtered. The

negative filter operation causes frames with the specified MAC

addresses to be forwarded.
You may easily prevent any station on one segment from accessing a

specific resource on the other segment; for this, “positive” filtering and

the use of “Filter if Destination” would be appropriate. If you want to

disallow a specific station from accessing any service, “Filter if Source”

could be used.

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