Programmable Filtering
Mask Combinations
Mask combinations may be required to ensure that a frame is sufficiently qualified before the decision to filter is made. The qualification a frame must go through before a filter decision is made depends on the reason for the filter. Nonetheless, a few examples below have been provided that should aid in the creation of a mask that may require that extra little bit of qualification.
Example
To prevent a specific Ethernet station from accessing any TCP/IP host on the other segment. Assume the Ethernet address is
The mask would be: 6-010203040506&12-0800&23-06
Example
To prevent a specific protocol type from accessing a specific Ethernet Address. Assume the Ethernet address is 01-
Example
To prevent any Ethernet address with the 10th bit set to a 0 from accessing a LAT host or an IP host with an Internet address of 128.001.001.128.
This particular mask, although not particularly useful, might be best served by creating two masks instead of one long mask. The decision is up to the Bridge Manager, but a longer mask is always more difficult to understand later. Both methods are presented below:
Combined Filters
Separate Filters
B.12 —