Alteon Application Switch Operating System Application Guide
Filtering and Traffic Manipulation
358 Document ID: RDWR-ALOS-V2900_AG1302
Stacking Filters
Stacking filters are assigned and enabled on a per-port basis. Each filter can be used by itself or in
combination with any other filter on any given port. The filters are numbered 1 through 2048. When
multiple filters are stacked together on a port, the filter number determines its order of precedence;
the filter with the lowest number is checked first. When traffic is encountered at the port, if the filter
matches, its configured action takes place and the rest of the filters are ignored. If the filter criteria
do not match, Alteon tries to match the criteria of the following filter.
As long as the filters do not overlap, you can improve filter performance by making sure that the
most heavily used filters are applied first. For example, consider a filter system where the Internet is
divided according to destination IP address:
Example Stacking Filters
Assuming that traffic is distributed evenly across the Internet, the largest area would be the most
used and is assigned to Filter 1. The smallest area is assigned to Filter 4.
Overlapping Filters
Filters are permitted to overlap, although special care must be taken to ensure the proper order of
precedence. When there are overlapping filters, the more specific filters (those that target fewer
addresses or ports) must be applied before the generalized filters. For example:
Example Overlapping Filters
In this example, Filter 2 must be processed prior to Filter 3. If Filter 3 is permitted to take
precedence, Filter 2 is never triggered.
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