User's Manual

In C class network, the applied number of IP addresses with network masking is as below when you
mask on host ID part (X4: the fourth byte).
Masking on X4 Byte Remark
Host ID
number
25
26 27 28 29 30 31 0 Masking Point
128
(128)
64
(192)
32
(224)
16
(240)
8
(248)
4
(252)
2
(254)
1
(255)
Decimal Number
(Accumulated Value)
Masked
Free Free Free Free Free Free Free 7 digits are free 2
7
= 128
Masked Free Free Free Free Free Free 6 digits are free 2
6
= 64
Masked Free Free Free Free Free 5 digits are free 2
5
= 32
Masked Free Free Free Free 4 digits are free 2
4
= 16
Masked Free Free Free 3 digits are free 2
3
= 8
Masked Free Free 2 digits are free 2
2
= 4
Masked Free 1 digits are free 2
1
= 2
Masked No free digit 2
0
= 1
The most common case is to make subnet through network masking, and it is to divide a network
into some smaller network. If provided IP address is 192.168.1.2, you may divide the whole
network into 2 sub-networks and allow or deny only the IP addresses that belong to one of
sub-networks.
With setting as follows, The IP address of 192.168.1.2 is divided into two sub-networks and allow
for the IP address out of the first sub-network to assess NetServer.
• Default Policy: Deny
• IP address: 192.168.1.2
• Masking: 25 (255.255.255.128)
• Then only the IP addresses from 192.168.1.0 to 192.168.1.127 are to access NetServer, while the
IP addresses from 192.168.1.128 to 192.168.1.255 and any other IP address are to be denied
accessing NetServer.
Changing IP address can reverse the result. If you set IP address as 192.168.1.130, only the IP
addresses from 192.168.1.128 to 192.168.1.255 are to access NetServer. And the IP addresses from
192.168.1.0 to 192.168.1.127 and any other IP address are to be denied accessing NetServer.
You may refer below table to figure out masking point from network information that is given from
your ISP or network administrator.
Masking Point Masked bit (Network ID) Netmask in decimal number
1 The first bit 128.0.0.0
2 From the first bit to the second bit 192.0.0.0