Perle Systems PERLE P850 - Manual (Page 67)

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3 - I
NTRODUCTION TO
F
ILTERING
The P850 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 P850 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.