Creating Packet Filters

12-15

4Enter executable instruction #3:

eq # if the two values on the top of the stack are equal,

# then return a non-zero value

Packet Filter Two. This filter is designed to accept packets within the socket range of 0x76c and 0x898. These steps show how to create this filter:

1Name the filter:

“Socket range filter”

2Enter executable instruction #1:

pushLiteral.w 0x76c #

put

the lowest socket value on top

#

of

the stack

3 Enter executable instruction #2:

pushField.w 30 # put the value

of the socket from the

# packet on top

of the stack

4Enter executable instruction #3:

ge #

compare

if

the value of the

socket is greater than

#

or equal

to

the lower bound

 

5 Enter executable instruction #4:

pushLiteral.w 0x0898 # put

the highest socket value on

# top

of the stack

6 Enter executable instruction #5:

pushField.w 30 # put the value

of

the

socket from the

# packet on top

of

the

stack

7Enter executable instruction #6:

lt

#

compare if the value of the socket is less than the

 

#

upper bound

8Enter executable instruction #7:

and # “and” together with “ge” and “lt” test to determine

#if the socket value is “within” the range. If it is,

#a “one” will be placed on the stack.

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3Com 2200 manual Enter executable instruction #3, Enter executable instruction #4, Enter executable instruction #5
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