What Happened to IPv5?

IPv5 was skipped in favor of IPv6

Visual representation of the internet
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An internet protocol is the set of rules that govern how packets are transmitted over a network. IPv5 is a version of internet protocol (IP) that was never formally adopted as a standard. The "v5" stands for version five of internet protocol. Computer networks use version four, typically called IPv4, or a newer version of IP called IPv6.

What happened to version five? People who study computer networking are understandably curious to know what happened to the protocol version in between, IPv5.

IPv5 Address Limitations

In short, IPv5 never became an official protocol. Many years ago, what is known as IPv5 started out under a different name: ​Internet Stream Protocol, or simply ST. The ST/IPv5 internet protocol was developed as a means of streaming video and voice data, and it was experimental. It was never transitioned to public use in part because of its 32-bit limitations.

IPv5 used IPv4's 32-bit addressing, which eventually became a problem. The format of IPv4 addresses is the ###.###.###.### format, made up of four numerical octets (a unit of digital information in computing consisting of eight bits), with each set ranging from 0 up to 255 and separated by periods. This format allowed for 4.3 billion internet addresses; however, the rapid growth of the internet soon exhausted this number of unique addresses. By 2011 the last remaining blocks of IPv4 addresses were allocated. With IPv5 using the same 32-bit addressing, it would have suffered from the same limitation.

So, IPv5 was abandoned before ever becoming a standard, and the world moved on to IPv6.

IPv6 Addresses

IPv6 was developed in the 1990s to solve the addressing limitation, and commercial deployment of this new internet protocol began in 2006. IPv6 is a 128-bit protocol, and it provides vastly more IP addresses. The format of IPv6 is a series of eight 4-character hexadecimal numbers, each of these representing 16 bits, for a total of 128 bits. The characters in an IPv6 address are numbers from 0 to 9 and letters from A to F.

An example of an IPv6 address is 2001:0db8:0000:0000:1234:0ace:6006:001e. IPv6 has the capacity to offer trillions upon trillions of IP addresses (as many as 3.4x1038 addresses) with little chance of running out anytime soon.

The format of an IPv6 address is long and often contains numerous zeros. Leading zeros in the address can be "suppressed" to shorten addresses. For example, the above IPv6 address may be expressed as the much shorter 2001:db8::1234:ace:6006:1e. Also, whenever there is a series of more than one 4-character set that consists of all zeros, these may be replaced with the "::" symbol (you may only use one :: symbol in an IPv6 address, however).