IP Addresses
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Networking Basics
IP Addresses
With the number of TCP/IP networks interconnected across the globe, ensuring that transmitted
data reaches the correct destination requires each computer on the Internet to have a unique
identifier. This identifier is known as the IP address. The Internet Protocol (IP) uses a 32-bit
address structure, and the address is usually written in dot notation.
A typical IP address looks like this:
198.25.12.8
The 32 bits of the address are subdivided into two parts. The first part of the address identifies
the network, while the second part identifies the host node or station on the network. How the
address is divided depends on the address range and the application.
The five standard IP address classes each have different methods to determine the network and
host sections of the address, which makes multiple hosts on a network possible. TCP/IP soft-
ware identifies each address class by reading a unique bit pattern that precedes each address
type. Once the address class has been recognized, the software can then correctly determine
the addresses’ host section. With this structure, IP addresses uniquely identify each network
and node.
Net Mask
With each address class, the size of the two subdivided parts (network address and host
address) is implied by the class. A net mask associated with an IP address can also express
this partitioning. A net mask 32-bit quantity yields the network address when combined with an
IP address. As an example, the net masks for Class A, B, and C are 255.0.0.0, 255.255.0.0, and
255.255.255.0 respectively.
Instead of dotted-decimal notation, the net mask can also be written in terms of the number of
ones from the left. This number is added to the IP address, following a back slash (/). For exam-
ple, a typical Class C address could be written as 192.168.234.245/24, which means that the
net mask is 24 ones followed by 8 zeros. (11111111 11111111 11111111 00000000).
Subnet Addressing
Subnet addressing enables the split of one IP network address into multiple physical networks.
These smaller networks are called subnetworks, and these subnetworks can make efficient use
of each address when compared to needing a different network number at each end of a routed
link. This technique is especially useful in smaller network environments, such as small office
LANs.
A Class B address provides 16 bits of node numbers, which enable 65,536 nodes. Since most
organizations don’t require such a large number of nodes, the free bits can be reassigned with
subnet addressing.
Multiple Class C addresses can be made from a Class B address. For example, the IP address
of 172.20.0.0 allows eight extra bits to use as a subnet address, since node addresses are lim-
ited to a maximum of 255. The IP address of 172.20.52.212 would be read as IP network
address 172.20, subnet number 52, and node number 212.
Besides extending the number of available addresses, this technique also allows a network
manager to design an address scheme for the network by using different subnets. This can be
useful when trying to distinguish other geographical locations in the network or other depart-
ments in the organization.
