Programmable Filtering
The Bridge Filter Patterns menu is located under the FILTER
Protocol Type Field
Within an Ethernet frame, a protocol field exists at octet 12 and 13. These two octets, or
Internet Protocol (IP)
The Internet Protocol (IP) is the most widely used protocol within an Ethernet environment. As a result there may be a need to restrict in one form or another this protocol traffic.
Filter all IP Packets
To prevent IP traffic from being passed across the bridged network, a mask must be created that represents this protocol type. The IP protocol type is 0800H.
Since the protocol field starts at octet location 12, the necessary filter mask to prevent IP traffic from traversing the bridged network is as follows:
The 12 is the offset into the Ethernet frame, the
In this example, whenever a frame is seen on the LAN port, for which this filter mask has been specified, with a protocol of type equal to IP, the frame will be filtered.
Note that when you filter on IP frames, all frames using the IP protocol will also be filtered. This includes TCP, UDP, SNMP, etc.
IP, and no more
This example performs just the opposite function to the above example. Only IP packets will be allowed to be passed across the bridged network.
For this function there must be a method to prevent all but IP packets from being filtered. For this the NOT (“~”) logical operator is used. The NOT operator specifies that the expression has to be FALSE before the frame is filtered. In other words, only frames that are NOT equal to the expression will be filtered and discarded.
To create this mask, the following expression is entered:
The parenthesis simply ensures that the NOT operator will apply to the entire expression.
In this case, whenever a frame is received, the frame will be filtered if the protocol type is NOT equal to 0800 (IP).
Only one filter pattern may be used that contains the NOT operator.
B.8 —