3Com 4007, Руководство по внедрению, Страница: 347 / 684

Long Custom Filter Example 347
4 Add an and statement to compare the results of step 2 with the results of
step 3:
and
# Compare if IP and in range.
This combination looks like this:
Combining All the Filters
Together, the packet filters work to perform the solution to the problem:
filtering the broadcast packets from the market data servers. These steps
show how to create this filter:
1 Name the filter:
name “Discard XNS & IP broadcast pkts w/in socket range”
2 Perform steps 2 through 8 as described earlier in “Packet Filter One.”
3 Perform steps 2 through 8 as described earlier in “Packet Filter Two.”
4 Add an and statement to compare the results of step 2 and the results of
step 3:
and
# compare if XNS & in range
5 Perform steps 2 through 4 as described earlier in “Combining a Subset of
the Filters.”
Name “Only IP pkts w/in socket range”
pushField.w 12 # Get the type field of the packet and
# place it on top of the stack.
pushLiteral.w 0x0800 # Put the type value for IP on top of
# the stack.
eq # If the two values on the top of the
# stack are equal, then return a non-zero
# value.
pushLiteral.w 0x76c # Put the lowest socket value on top of
# the stack (1900).
pushField.w 24 # Put the value of the socket from the
# packet on top of the stack.
ge # Compare if the value of the socket is
# greater than or equal to the lower bound
pushLiteral.w 0x0898 # Put the highest socket value on top of
# the stack (2200).
pushField.w 24 # Put the value of the socket from the
# packet on top of the stack.
lt # Compare if the value of the socket is
# less than the upper bound.
and # “and” together with “ge” and “lt” test
# to determine if the socket value is
# “within” the range. If it is in range,
# place a “one” will on the stack.
and # Compare if IP and in range.