User's Manual
D 224 to 239 For Multicasting utilization
E 240 to 255 Reserved for specific utilization
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 NetCam-2.
• 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 NetCam-2, while the IP
addresses from 192.168.1.128 to 192.168.1.255 and any other IP address are to be denied accessing
NetCam-2.
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 NetCam-2. And the IP addresses from 192.168.1.0 to
192.168.1.127 and any other IP address are to be denied accessing NetCam-2.
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
3 From the first bit to the third bit 224.0.0.0