INTERNET PROTOCOL ADDERSS

Internet Protocol address

An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing.

IP addresses must be unique for each computer connected to a network. That means that if you have two computers on your network, each must have a different IP address. If by accident, the same IP address is assigned to two computers, then those computers would have what is called an "IP Conflict" and not be able to communicate with each other.

The designers of the Internet Protocol defined an IP address as a 32-bit number and this system, known as Internet Protocol Version 4 (IPv4), is still in use today. However, due to the enormous growth of the Internet and the predicted depletion of available addresses, a new version of IP (IPv6), using 128 bits for the address, was developed in 1995.

IP addresses are binary numbers, but they are usually stored in text files and displayed in human-readable notations, such as 172.16.254.1 (for IPv4), and 2001:db8:0:1234:0:567:8:1 (for IPv6).

IPv4 and IPv6 Addresses

There are two types of IP Addresses that can be used on a network. The first, and the version that the Internet and most routers are currently configured for, is IPv4 or Internet Protocol version 4. This version uses 32-bit addresses, which limits the amount of addresses to 4,294,967,296 possible unique addresses. Due to the popular growth of the Internet there has been concern that the pool of possible addresses would be exhausted in the near future. With this in mind, a new version of IP addresses was developed called IPv6, or Internet Protocol version 6, that would change the address size from 32-bit address to 128-bit addresses. This change would allow for generous IP address allocations to networks without any foreseeable problem with the amount of addresses available.

IPv4 addresses

In IPv4 an address consists of 32 bits which limits the address space to 4294967296 (2³²) possible unique addresses. IPv4 reserves some addresses for special purposes such as private networks (~18 million addresses) or multicast addresses (~270 million addresses).

An IP address always consists of 4 numbers separated by periods, with the numbers having a possible range of 0 through 255. An example of how an IP address appears is: 172.16.254.1

This representation of an IP address is called decimal notation and is what is generally used by humans to refer to an IP address for readability purposes. With the ranges for each number being between 0 and 255 there are a total 4,294,967,296 possible IP addresses.

Out of these 4,294,967,296 addresses there are 3 special addresses that are reserved for special purposes. The first is the 0.0.0.0 address and refers to the default network and the 255.255.255.255 address which is called the broadcast address. These addresses are used for routing. The third address, 127.0.0.1, is the loopback address, and refers to your machine. Whenever you see, 127.0.0.1, you are actually referring to your own machine. That means if you clicked on this link, http://127.0.0.1, you are actually trying to connect to your own computer, and unless you have a web server running, you will get a connection error. So, the IP addresses 0.0.0.0 and 255.255.255.255 are reserved, and are not considered usable IP addresses.

 
Introduction to  classes

 

The number of addresses usable for addressing specific hosts in each network is always 2^N - 2 (where N is the number of rest field bits, and the subtraction of 2 adjusts for the use of the all-bits-zero host portion for network address and the all-bits-one host portion as a broadcast address. Thus, for a Class C address with 8 bits available in the host field, the number of hosts is 254.

 

 

Bit-wise representation

 

In the following table:

• n indicates a binary slot used for network ID.
• H indicates a binary slot used for host ID.
• X indicates a binary slot (without specified purpose)

Class A

  0.  0.  0.  0 = 00000000.00000000.00000000.00000000

127.255.255.255 = 01111111.11111111.11111111.11111111

                  0nnnnnnn.HHHHHHHH.HHHHHHHH.HHHHHHHH

Class B

128.  0.  0.  0 = 10000000.00000000.00000000.00000000

191.255.255.255 = 10111111.11111111.11111111.11111111

                  10nnnnnn.nnnnnnnn.HHHHHHHH.HHHHHHHH 

Class C

192.  0.  0.  0 = 11000000.00000000.00000000.00000000

223.255.255.255 = 11011111.11111111.11111111.11111111

                  110nnnnn.nnnnnnnn.nnnnnnnn.HHHHHHHH 

Class D

224.  0.  0.  0 = 11100000.00000000.00000000.00000000

239.255.255.255 = 11101111.11111111.11111111.11111111

                  1110XXXX.XXXXXXXX.XXXXXXXX.XXXXXXXX

Class E

240.  0.  0.  0 = 11110000.00000000.00000000.00000000

255.255.255.255 = 11111111.11111111.11111111.11111111

                  1111XXXX.XXXXXXXX.XXXXXXXX.XXXXXXXX

Description of IP classes

Listed below are descriptions of the IP classes and the organizations that will typically receive that type of allocation. 

Default Network: The special network 0.0.0.0 is generally used for routing.

Class A: From the table above you see that there are 126 class-A networks. These networks consist of 16,777,214 possible IP addresses that can be assigned to devices and computers. This type of allocation is generally given to very large networks such as multi-national companies.

Loopback: This is the special 127.0.0.0 network that is reserved as a loopback to your own computer. These addresses are used for testing and debugging of your programs or hardware.

Class B: This class consists of 16,384 individual networks, each allocation consisting of 65,534 possible IP addresses. These blocks are generally allocated to Internet Service Providers and large networks, like a college or major hospital. 

Class C: There are a total of 2,097,152 Class C networks available, with each network consisting of 255 individual IP addresses. This type of class is generally given to small and mid-sized 

   
Class D: The IP addresses in this class are reserved for a service called Multicast. The IPv4 networking standard defines Class D addresses as reserved for multicast. Multicast is a mechanism for defining groups of nodes and sending IP messages to that group rather than to every node on the LAN (broadcast) or just one other node (unicast).

Multicast is mainly used on research networks. As with Class E, Class D addresses should not be used by ordinary nodes on the Internet.

Class E: The IP addresses in this class are reserved for experimental use. The IPv4 networking standard defines Class E addresses as reserved, meaning that they should not be used on IP networks. Some research organizations use Class E addresses for experimental purposes. However, nodes that try to use these addresses on the Internet will be unable to communicate properly.

Broadcast: This is the special network of 255.255.255.255, and is used for broadcasting messages to the entire network that your computer resides on.

All computers that belong to a subnet are addressed with a common, identical, most-significant bit-group in their IP address. This results in the logical division of an IP address into two fields, a network or routing prefix and the rest field or host identifier. The rest field is an identifier for a specific host or network interface.

All hosts on a sub-network have the same network prefix. This routing prefix occupies the most-significant bits of the address.

The routing prefix is expressed in CIDR notation. It is written as the first address of a network, followed by a slash character (/), and ending with the bit-length of the prefix. For example, 192.168.1.0/24 is the prefix of the Internet Protocol Version 4 network starting at the given address, having 24 bits allocated for the network prefix, and the remaining 8 bits reserved for host addressing.

In IPv4 the routing prefix is also specified in the form of the subnet mask, which is expressed in quad-dotted decimal representation like an address. For example, 255.255.255.0 is the network mask for the 192.168.1.0/24 prefix.

The routing prefix of an address is written in a form identical to that of the address itself. This is called the network mask, or net-mask, of the address. For example, a specification of the most-significant 18 bits of an IPv4 address, 11111111.11111111.11000000.00000000, is written as 255.255.192.0. If this mask designates a subnet within a larger network, it is also called the subnet mask. This form of denoting the network mask, however, is only used for IPv4 networks.

 

 

IPv4 sub-netting

The process of subnetting involves the separation of the network and subnet portion of an address from the host identifier. This is performed by a bitwise AND operation between the IP address and the (sub)network mask. The result yields the network address or prefix, and the remainder is the host identifier.

 

Determining the network prefix

An IPv4 network mask consists of 32 bits, a sequence of ones (1) followed by a block of 0s. The trailing block of zero (0) designates that part as being the host identifier.

The following example shows the separation of the network prefix and the host identifier from an address (192.168.5.130) and its associated /24 network mask (255.255.255.0). The operation is visualized in a table using binary address formats.

	Binary form	Dot-decimal notation
IP address	11000000.10101000.00000101.10000010	192.168.5.130
Subnet mask	11111111.11111111.11111111.00000000	255.255.255.0
Network prefix	11000000.10101000.00000101.00000000	192.168.5.0
Host part	00000000.00000000.00000000.10000010	0.0.0.130

The mathematical operation for calculating the network prefix is the bitwise AND of IP address and subnet mask. The result of the operation yields the network prefix 192.168.5.0 and the host number 130.