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Packet Filters 8-9
Destination Address
The address given here is compared to the destination address
of the packet. Note that only the part of the address specified by
the mask field is used in the comparison. If a match is found, the
packet is forwarded (rules containing permit) or discarded
(rules containing deny).
The following rule example denies destination addresses that
match the first 8 bits of the given IP address (that is, addresses
beginning with 192):
deny 0.0.0.0/0 192.77.200.203/8
Masks
These fields specify the number of bits to be used in the source
address and destination address comparisons. Valid values are
0–32. Common bit counts are:
0 Match packets with any IP address. The contents of the
source address or destination addr ess field are not
important.
8 Compare the first byte (octet) in the IP addresses.
16 Compare only the first two bytes of the IP addresses
24 Compare only the first three bytes of the IP Addresses
32 Match the entire IP address
The masks are separated from source address and destination
address by forward slashes (/).