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The Internet Protocol (IP) is a packet-based protocol used to exchange data over computer networks. It is 
the foundation on which all other IP protocols are built. IP is a network-layer protocol that contains 
addressing and control information that allows data packets to be routed. 
 
This section describes how to configure the Internet Protocol (IP). 
 

 
A number of tasks are associated with configuring IP. A basic and required task for configuring IP is to 
assign IP addresses to network interfaces. Doing so enables the interfaces and allows communication with 
hosts on those interfaces using IP. Associated with this task are decisions about subnetting and masking the 
IP addresses. 
 

 
An IP address is a location to and from which IP datagrams can be sent. IP addresses were traditionally 
divided into three classes. The Class A Internet address format allocated the highest eight bits to the 
network field and set the highest-order bit to 0 (zero). The remaining 24 bits formed the host field. The Class 
B Internet address allocated the highest 16 bits to the network field and set the two highest-order bits to 1, 0. 
The remaining 16 bits formed the host field. The Class C Internet address allocated the highest 24 bits to the 
network field and set the three highest-order bits to 1,1,0. The remaining eight bits formed the host field. 
 
The table below lists the traditional classes and ranges of IP addresses, and their status. 
 

Class 

Address or Range 

Status 

A 0.0.0.0 

1.0.0.0 to 126.0.0.0 
127.0.0.0 
 

Reserved 
Available 
Reserved 

B 128.0.0.0 

to 

191.254.0.0 

191.255.0.0 

Available 
Reserved 

C 192.0.0.0 

192.0.1.0 to 223.255.254 
223.255.255.0 

Reserved 
Available 
Reserved 

D 

224.0.0.0 to 239.255.255.255 

Multicast group addresses 

E 240.0.0.0 

to 

255.255.255.254 

255.255.255.255 

Reserved 
Broadcast 

 
 
With the rapid expansion of networks being connected to the Internet, critical problems were seen with the 
traditional classified addressing scheme. It was possible that IP addresses would run out, and routing tables 
would be overwhelmed. Thus, the Classless Inter-Domain Routing (CIDR) addressing scheme was created. 
 
CIDR replaces the older process of assigning IP addresses with general prefixes of 8, 16, or 24 bits. CIDR 
uses prefixes of 13 to 27 bits. A CIDR address includes the standard 32-bit IP address and adds information 
on how many bits are used for the network prefix. In the IP address 206.203.1.35/27, the “/27” indicates that 
the first 27 bits are used to identify the unique network, and the remaining bits are used to identify the 
specific host. Now, blocks of addresses can be better fitted to even very small or very large networks. The 
following table describes the Class C equivalent of CIDR prefixes.