ip numberAn IP address is the unique identifier that the Internet Protocol (IP) assigns each node or host in a network. A host is anything that requires a connection and communication with other hosts over the network. Hosts can be computers (servers & PCs), network printers, smartphones, tablets, even TVs and fridges. A network is a group of two or more hosts that connect together using a common protocol (language) of communication. Today the most popular and widespread method of connecting hosts is by Ethernet or Wi-Fi, and the most popular protocol is IP.

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An IP address is actually a 32-bit binary address as computers and the processors imbedded within other hosts talk in binary. However to be human readable they are referred to in dot-decimal notation, which consists of four decimal number, separated by dots, each being between 0 and 255. Therefore, the 32-bit binary address is split into four octets (8 bit) and maps to four decimal numbers separated by a dot.

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All IPv4 addresses conform to this four-byte format.

IP has been around a long time and so its method of addressing has evolved as circumstance dictated. During the pre-internet days, IP addresses were used freely and without any real consensus as too what part was the network and what part was for hosts. Clearly for the protocol to succeed there had to be an agreed structure so that anyone receiving an addressed packet could ascertain what was the network it belonged to and what was its host identifier. The resulting standard was the IP Classes A, B, C & D, with a fifth E reserved.

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Class A addresses were handed out to technology companies such as IBM, Microsoft and Apple. The class B address space was designated for large companies and Universities and class C addresses were designated for small companies. This was the standard policy for some time until the early 90s came the rapid expansion of the Internet. In response to the huge demand for IP addresses, and in much smaller segments, IANA introduced CIDR (Classless Inter Domain Routing) in 1993. CIDR is based on variable length subnet masking (VLSM), which does not have fixed network and host segments. Instead it allows the boundary to be flexible. The advantage of having a flexible mask is it allows the network designer to adjust the mask to create any size of subnet.

VLSM was the bases of flexible length subnet masking and this made the notion of fixed classes redundant. VLSM works on the principle of bit borrowing by designating the subnet mask to land on any bit boundary. No longer were there legacy class boundaries of eight, sixteen and twenty-four relevant. Now a boundary could sit at seventeen or twenty-eight. As a result the flexible subnet mask was introduced represented by either a shorthand /(no of bits) such as /8 or as the traditional dot-decimal notation.

The growth of the Internet also determined change in other respects. Prior to the Internet, IP addresses were assigned to whoever asked in class blocks. There was no real demand and therefore no shortage of IP addresses. In hindsight it was a wasteful policy. With the explosive surge in demand for IP addresses in the mid-nineties, it became clear that IPv4, despite its seemingly vast address space of 2^32 or over four billion addresses, was unsustainable. In order to address the problem, private IP addresses were introduced.

Private IP addresses were a tactical move to mitigate the problem of chronic IP address shortage. Three blocks of addresses, taken from the original IP address classes A, B and C were designated as private and they were reserved only for use within the boundaries of private networks.

Address Range

Address block

Largest CIDR Block –

24 bit

/8 –

20 bit

/12 –

16 bit



IANA designated these ranges of IP addresses for use by anyone to address their own private networks. This decision was based on the assumption that very few computers in use in private business or government actually needed to be connected to the internet. This was indeed the case and network administrators slowly began to adopt private addressing within their business networks. Private addressing became more readily accepted as reports of security issues with the Internet began to emerge. However, it was a newly emerging technology that made private addressing not just grudgingly acceptable to businesses but downright desirable; Network Address Translation.

NAT or network address translation is a technology implemented in routers and firewalls that translates private (illegal/meaningless on the Internet) addresses to real public IP addresses. This meant that computers configured with a private address could now access the internet via the router or firewall. Administrators could manage these single points of exit using access-lists and the real beauty was it was one way. A computer with a private address could initiate communications with a website on the internet, but the computer was safe from being accessed directly from the internet.

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Private addressing and NAT went a long way to prolong the life expectancy of IPv4 as did virtual hosting of websites, and internet cloud services. It was not to last as other disruptive products sent demand for IP rocketing. ADSL and smartphone technology along with tablets have sent IPv4 once again to the brink of exhaustion. Business interest in the successor technology IPv6 has been cool to say the least with every year passing by with more and more excuses for not migrating across.

IPv6 solves all the problems of IPv4 a limitless supply of addresses – where have we heard that before – automatic addressing, and no more sub-netting headaches. IPv6 is the future, there is no one that will contest that, but adoption has been painfully slow. Perhaps that should be interpreted as IPv4’s greatest compliment.

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