Allied Telesis x900-24 series manual Example 2 ports, Example 3 ports

Appendix A: How to use the layer 4 mask in classifiers

Example 2: ports 5004-5008

In some more complex situations, we may need more than one classifier to cover all the range we want to. Let’s take UDP destination ports between 5004-5008

5004	=	00010011 10001100
5005	=	00010011 10001101
5006	=	00010011 10001110
5007	=	00010011 10001111
5008	=	00010011 10010000

According to the bolded bits, we may think that the changed bits are the last 5 bits so the mask should be 11111111 11100000.

But remember that if we set the last 5 bits to 0, the mask will cover 25 = 32 ports. But we want to cover only 5 ports, so let’s divide 5 into 4+1.

5004	=	00010011 10001100
5005	=	00010011 10001101
5006	=	00010011 10001110	4	ports
5007	=	00010011 10001111
			+
5008	=	00010011 10010000	1	port

Now it is really easy to write the classifiers!

create class=1 udpdp=5004 l4dmask=FFFC

create class=2 udpdp=5008

add swi hwfilt class=1,2 action=drop

Example 3: ports 333-777

A more complex situation, let’s try to write the classifiers for UDP ports between 333-777. As we are trying to get rid of odd numbers in the beginning of our port range, we will prefer to write classifiers for single port number for 333.

z777-334+1 = 444 total number of port (+1 for including 333)

z256 + 128 + 32 + 16 + 8 + 4 = 444 (7 classifiers)

z7 classifiers + 1 classifier (for 333) = 8 classifiers

Now the question is how to locate these blocks. The short-cut to do that is, first, find the position of the biggest block, which is 256 for our example. 256 should fit into one of the following blocks:

0	-	255
256	-	512
512	-	767

768- 1024

...

65280 - 65536

Page 15 AlliedWare™ OS How To Note: Hardware Filters