The filter tracking feature is enabled for an X4 Ethernet adapter by default. The operation is transparent to the user/applications. When enabled, the firmware keeps track of which filters have been installed via each datapath. If needed, the firmware automatically adds extra entries to the FC to ensure that the most specific filter is correctly applied for each packet. This is needed as otherwise a less specific filter via the Express datapath could steal traffic away from a more specific filter on the Enterprise datapath when the two filters overlap.
Some consequences of filter tracking are:
- The maximum number of filters which can be used is reduced.
- The FC table is smaller than the Enterprise filter table, and could fill more quickly as some filter combinations require an entry in both tables.
- Firmware needs to store additional filter metadata for tracking.
- The FC only supports a subset of filter types. For example, IPv6 filters are not available.
- Some filter combinations are not possible when tracking is enabled.