Waters Network Systems
2800M/MR User’s Manual
Page 19
Class C:
IP address range between 192.0.0.0 and 223.255.255.255. Each class C network has a 24-bit
network prefix followed 8-bit host address. There are 2,097,152 (2^21)/24 networks able to be
defined with a maximum of 254 (2^8 –2) hosts per network.
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Class D and E:
Class D is a class with first 4 MSB (most significance bit) set to 1-1-1-0 and is used for IP
Multicast. See also RFC 1112. Class E is a class with first 4 MSB set to 1-1-1-1 and is used for
IP broadcast.
According to IANA (internet assigned numbers authority), there are three specific IP address
blocks reserved and able to be used for extending internal networks. This is referred to as
Private IP address and listed below:
Class A
10.0.0.0 --- 10.255.255.255
Class B
172.16.0.0 --- 172.31.255.255
Class C
192.168.0.0 --- 192.168.255.255
Please refer to RFC 1597 and RFC 1466 for more information.
Subnet mask:
Subnet mask is the sub-division of a class-based network or a CIDR block. The subnet is used
to determine how to split an IP address to the network prefix and the host address in bitwise
basis. It is designed to utilize the IP address more efficiently and make it easier to manage IP
networks.
For a class B network, 128.1.2.3, the subnet mask 255.255.0.0 in default, in which the first two
bytes are all 1s. This means more than 60 thousands of nodes in flat IP address will be at the
same network. This is too large to manage practically. Now if we divide it into a smaller network
by extending network prefix from 16 bits to, say 24 bits, its third byte is used to subnet this class
B network. Now it has a subnet mask 255.255.255.0, in which each bit of the first three bytes is
1. It’s now clear that the first two bytes is used to identify the class B network, the third byte is
used to identify the subnet within this class B network and, of course, the last byte is the host
number.
Not all IP addresses are available in the sub-netted network. Two special addresses are
reserved. They are the addresses with all zero’s and all one’s. For example, an IP address
128.1.2.128, what will the reserved IP address look like? All 0s mean the network itself, and all
1s mean IP broadcast.
Bit # 0 1 2 3 23 24 31
Network address Host
