Draytek Vigor2500V Manual page 67

Address will prevent this rule from being applied to that IP
address. It is equal to the logical NOT operator.
Subnet Mask: Specifies the Subnet Mask for the IP Address
column for this filter rule to apply to.
Operator: The operator column specifies the port number settings.
If the Start Port is empty, the Start Port and the End Port
column will be
number.
= : If the End Port is empty, the filter rule will set the port
number to be the value of the Start Port. Otherwise, the port
number ranges between the Start Port and the End Port
(including the Start Port and the End Port).
!= : If the End Port is empty, the port number is not equal to
the value of the Start Port. Otherwise, this port number is not
between the Start Port and the End Port (including the Start
Port and End Port).
> : Specifies the port number is larger than the Start Port
(includes the Start Port).
< : Specifies the port number is less than the Start Port
(includes the Start Port).
Keep State (Stateful Packet Inspection): When checked,
protocol information about the TCP/UDP/ICMP communication
sessions will be kept by the IP Filter/Firewall (the Firewall Protocol
option (see page 5-21) requires that TCP or UDP or TCP/UDP or
ICMP be selected for this to operate correctly).
Firewall
ignored. The filter rule will filter out any port
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