In a TCP/IP environment, end stations communicate seamlessly with servers or other end stations. This communication occurs because each node using the TCP/IP protocol suite has a unique 32-bit logical IP address. Each IP datagram includes the source IP address and destination IP address that identifies the source and destination network and host. Each company listed on the internetwork is seen as a single network that must be reached before an individual host within that company can be contacted.
Each company network has a unique two-part network address:
- The hosts that populate that network share those same bits, or network number.
- The remaining bits, or host number, are a unique identifier of each host within that network.
Examining IP Address Classes
There are only eight network bits in the Class A address, and 24 bits in the host field. So, few Class A networks, each consisting of many hosts, exist. There are more Class B and Class C networks, each with fewer hosts. This scheme allows the addresses to be assigned based on the size of the network. This address design was based on the assumption that there would be many more small networks than large networks in the world.
Class A addresses
include the following:
- The first bit is 0.
- Range of network numbers: 1.0.0.0 to 126.0.0.0
- Number of possible networks: 127 (1-126 usable, 127 is reserved)
- Number of possible values in the host portion: 16,777,216 (The number of usable hosts is two less than the number of possible because the host portion must be nonzero and cannot be all ones.)
Class B addresses
include the following:
- The first two bits are 10.
- Range of network numbers: 128.0.0.0 to 191.255.0.0
- Number of possible networks: 16,384
- Number of possible values in the host portion: 65,536 (The number of usable hosts is two less than the number of possible because the host portion must be nonzero and cannot be all ones.)
Class C addresses
include the following:
- The first three bits are 110.
- Range of network numbers: 192.0.0.0 to 223.255.255.0
- Number of possible networks: 2,097,152
- Number of possible values in the host portion: 256 (The number of usable hosts is two less than the number of possible because the host portion must be nonzero and cannot be all ones.)
Class D addresses
include the following:
- Range of network numbers: 224.0.0.0 to 239.255.255.255
What is a Subnet?
By breaking up the network into smaller segments, or subnets, network address use is more efficient. There is no change to how the outside world sees the network, but within the organization, there is additional structure.
Subnet Masks
A network device uses a subnet mask to determine what part of the IP address is used for the network, the subnet, and the device (host) address. A device can also determine the class of address it has been assigned from its own IP address. The subnet mask then tells the device where the boundary is between the subnet ID and the host ID. A subnet mask is a 32-bit value, written as four octets, containing a number of one bits for the network and subnet ID, and a number of zero bits for the host ID.
Each bit in the subnet mask is used to determine how the corresponding bit in the IP address should be interpreted as follows:
- Binary 1 for the network bits
- Binary 1 for the subnet bits
- Binary 0 for the host bits