American Fibertek SM8P-SFP - Manual (Page 30)

Rev.A1
18-May-11 22
10
Bit # 01 2 15 16 31
Network address Host address
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.
Bit # 0 1 2 3 23 24 31
Class D and E:
110
Network address Host address
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
network. We call it Private IP address and list 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:
It means 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 IP address more efficiently and
ease to manage IP network.
For a class B network, 128.1.2.3, it may have a subnet mask 255.255.0.0 in
default, in which the first two bytes is with all 1s. This means more than 60
thousands of nodes in flat IP address will be at the same network. It’s too large to
manage practically. Now if we divide it into smaller network by extending network
prefix from 16 bits to, say 24 bits, that’s using its third byte 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.