IPv6 and IPv4

There are two versions of Internet Protocol (IP)  in use: IP version 4 (IPv4) and IP version 6 (IPv6).


IPv4 was the first version to be widely used, and still accounts for most of today’s Internet traffic. The total size of the IPv4 address pool will not support the growing numbers of Internet devices and available supplies have run out in four of the five RIR service regions. Each IPv4 address consists of 32 bits and addresses are often formatted into a dotted decimal notation such as Each byte is a number between 0 and 255.


IPv6 provides far more addresses than IPv4 and is deployed in networks all over the globe. An IPv6 address consists of 128 bits, usually written as eight groups of four hexadecimal characters, such as 2001:DB8::/32. A double colon (::) may replace sets of consecutive zeros.

The main deployment model for IPv6 is “dual-stacking,” where operators support both IPv4 and IPv6 in their networks. The two protocols both operate across the Internet and most users will never be aware of which address protocol is responsible for delivering their emails or downloading their web pages.

IP version IPv4 IPv6
Deployed 1981 1999
Address Size 32-bit number 128-bit number
Address Format Dotted Decimal Notation: Hexadecimal Notation: 2001:0DB8:0234:AB00: 0123:4567:8901:ABCD
Number of Addresses 232 = 4,294,967,296 2128 = 340,282,366,920,938,463,463,374,607,431,768,211,456
Examples of Prefix Notation 10/8 (a “/8” block = 1/256th of total IPv4 address space = 224 = 16,777,216 addresses) 2001:0DB8:0234::/48 2600:0000::/12


Like IP addresses, Autonomous System Numbers (ASNs)  are important Internet number resources. As the Internet has expanded over time, the original pool of available ASNs has dwindled, and they are now running out.

As a result, engineers have adjusted the ASN specification from two bytes to four bytes. This means that the pool of ASNs has grown from around 65,000 to over 4 billion.

Network managers and ICT vendors need to be aware of these changes and act now to ensure their networks and products are compatible with the new ASNs.

Last modified on 30/07/2018