IP Address

An IP (Internet Protocol) address is a unique address that different computers on a computer network use to identify and communicate with one another. An IP address is used as an identifier to find electronic devices connected to one another on a network. Therefore, each device in the network must have its own unique address. An IP address is like a mailing address that is used to deliver data (files) to a computer.

Some IP addresses are meant to be unique within the scope of the Internet, whereas others are meant to be unique within the scope of a specific network. The Internet Assigned Numbers Authority (IANA) creates and manages IP addresses for the public Internet. IANA allocates the superblocks of addresses to Regional Internet Registries, which in turn allocate smaller blocks of addresses to Internet service providers.

An IP address is 32 (thirty two) bits long, which can be divided into a network portion and a host portion with the help of a subnet mask. It is represented in the form of four octets, where 1 octet = 8 bits. Each octet is converted to a decimal format and is separated by a dot (.). For this reason, an IP address is said to be expressed in a ‘dotted decimal format.’

Examples of IP addresses in decimal format: 10.1.1.1, 255.255.255.255, 220.3.1.5

The value in each octet ranges from 0 to 255 in decimal format. The ‘dotted decimal format’ makes it easier for humans to read and remember the numbers, but computers use IP addresses in a binary format only.

Example of an IP address in binary format: 10011101.11100010.10101110.11101000

Binary Octet to Decimal Format Conversion

There exists a well defined method for converting binary IP addresses into its equivalent decimal format and vice versa. Humans prefer to operate on the dotted decimal format, whereas behind the curtain, computers deal with IP addresses in the binary form.

The right most bit or the least significant bit of an octet holds a value of 20. The bit just to the left of it has a value of 21. This series continues until the left most 8th bit gets a value of 27. Hence, if all the binary bits of an octet are 1, then the decimal equivalent would be 255.

11111111 (binary octet) = 1 + 2 + 4 + 8 + 16 + 32 + 64 + 128 = 255 (decimal format)

Below is an example where all octet bits are not 1.

01000001 (binary octet) = 1+0+0+0+0+0+64+0 = 65 (decimal format)

Static and Dynamic IP Addresses

An IP address can be static or dynamic. If the computer uses the same IP address whenever it connects to the network, it is said to have a static IP address. If the IP address changes frequently whenever the computer connects to the network, it is said to have a dynamic IP address. The network administrator manually assigns static IP addresses, whereas the Dynamic Host Configuration Protocol (DHCP) assigns dynamic IP addresses. An operating system can also assign itself a dynamic address when a DHCP server and the network administrator are unavailable. The operating system uses Zero-conf for this purpose. Dynamic addresses are usually used for LANs and broadband networks, whereas static addresses locate servers within an enterprise.

At present, two versions of Internet Protocol are in use: IPv4 and IPv6. IPv4 uses 32-bit addresses, so its address space is limited to 4,294,967,296 unique addresses, with a large part reserved for special purposes. So, fewer addresses are available for the public Internet. IPv6 was designed as a replacement for IPv4, as the addresses are 128 bits wide. Therefore, IPv6 offers a large address space.

Types of IP Addresses

• Unicast IP Address : It is used to transmit information to a specific network device on the network.
• Broadcast IP Address : It allows information to be sent to all the computers on a given subnet rather than a particular machine. The exact notation can differ by the operating system, but the standard is laid out in RFC 919. Each and every machine on the subnet receives the IP packets directed to the broadcast address. It is generally used for mass communication such as a radio transmission to multiple listeners.
  The broadcast address is calculated by taking the bit complement of the subnet mask and then applying OR operating bitwise with the IP address.Example: To broadcast a packet to an entire class B subnet with a private IP address space, the broadcast address would be 172.16.255.255. This can be done with the help of the subnet mask; 255.255.0.0, and the IP address; for e.g. 172.16.48.196. The complement of the subnet mask is 0.0.255.255 and 172.16.48.196 || 0.0.255.255 = 172.16.255.255.

  255.255.255.255 is a limited broadcast IP address, which does not reach every node on the Internet only nodes on LAN.

• Multicast IP Address : Multi-cast IP addresses are reserved and used only for specific groups of machines residing in a large domain. For example, an IP packet destined for a multi-cast address will be sent only to machines that are part of that Multi-cast Group. The address range of class D IP addresses from 224.0.0.0 to 239.255.255.255, or equivalent 224.0.0.0/4, is particularly reserved for Multicasting.
  Examples are RIP, which uses 224.0.0.9 and OSPF, which uses 224.0.0.5 address.
• Private IP Address : These are local addresses that cannot be routed over the Internet. Two organizations can use the same private IP address. These addresses are free for everyone.
• Public IP Address : It is a unique IP address that IANA (Internet Assigned Network Authority) assigns. Duplication of the public IP addresses is impossible. Hence, these addresses need to be bought.