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IPv4 & IPv6

The Internet Protocol Saga – Where is IPv5?

IP addresses are like Star Wars movies. Lots of versions, some of which are better than others, confusing numbering, and a long history of technological improvements.

Nowadays, IPv4 is still the most preferred version of the Internet Protocol, even if IPv6 is the more advanced and flexible variant. IPv4’s omnipresence is a well-known fact, but have you ever wondered where all the other versions went?

What happened to IPv5? What’s with the sudden jump to IPv6? To get a better understanding of this discrepancy, we should have a look at the entire Internet Protocol family, with its prequels and sequels.

The original trilogy

The Internet is way older than you think. In fact, back in the 60s and 70s, network engineers were pretty busy working on what now allows us to share an entire online world.

Before the birth of the IP we know today, there was the Transmission Control Protocol (TCP). TCP is one of the main protocols that make up the Internet Protocol suite, commonly known as TCP/IP. 

Back in those years, TCP and IPs were designed to complement each other and allow internetworking, meaning communication between computers.

Between 1973 and 1978, engineers played with different versions of TCP/IP, up until the point they came up with IPv1, IPv2, and IPv3. These versions were designed to improve upon the primordial TCP/IP. For example, IPv3 was designed to separate the functionalities of TCP/IP, as they were previously merged. It also proposes different versions of the modern IP header.

Versions 1 to 3 never went past the experimental stage, so regular Internet users never had the chance to work with them.

The current IPv4 is a mistake

Interestingly enough, the documents about IPv1 to 3 also mention different versions of our all-time favorite IPv4. And even more surprisingly, versions 1, 2, and a prototype of IPv4 allowed an address length of 128 bits.

As you might already know, the modern IPv4 has a modest 32-bit space, while IPv6 is the only current bearer of the 128-bit format. How did it come to that? By mistake. Literally. It appears that in the final version of IPv4, the address length was accidentally reduced to 32 bits. 

The lost tapes – Where is IPv5?

Technically speaking, IPv5 never actually existed. In fact, there was never an Internet Protocol version 5. This was just another name for the Internet Stream Protocol, or ST, for short.

ST was first introduced in 1979, and developed collectively by Apple, NeXT, and Sun Microsystems. It remained experimental, and its purpose was to stream human speech across networks.

Internet Stream Protocol had a second version in the works, namely ST2 (some sort of…IPv5 v2.0). The improved iteration was specifically designed to allow video streaming. 

Neither version of the Internet Stream Protocol ever made its way out into the wild. By the time ST and ST2 were ready to become publicly available for testing, IPv6 was already on a roll.

Why did IPv5 fail?

First, it is important to clear the confusion regarding IPv5’s failure. It did not fail as a member of the IP address family, because it did not exist as a predecessor to IPv6.

IPv5 failed to become an official protocol due to its limitations. The name ”IPv5” was given to ST and ST2 simply because the creators wanted to distinguish ST and IPv4 packet headers. As a result, IPv5 was included in the ST packet header.

Following that, engineers figured out this might still create some confusion, and decided to jump straight ahead to IPv6 for the next iteration of the Internet Protocol.

The major disadvantage that pulled the plug on IPv5 was its addressing space. Like IPv4, the fifth version was based on a 32-bit format. 

In the early days of the Internet, the 32-bit format seemed to be enough, as it allowed for up to 4,3 billion unique IP addresses. But the Internet grew so fast and so much that the IPv4 pool started running short.

IPv5 made use of the same addressing space, and by the time ST2 came out, the IPv4 depletion process had already begun. Naturally, introducing another protocol that could not support the Internet infrastructure for long was a waste of time and resources.

IPv6 is the official successor to IPv4

IPv6 is a result of several years of experimentation where multiple models were proposed. The standardized and official IPv6 format was launched in 1998 and its 128-bit addressing space seems to be the optimal solution for the IPv4 shortage.

With trillions upon trillions of unique addresses, IPv6 is the true successor to IPv4 and the format that will help billions and billions of devices go online.

Is IPv6 better than IPv4? That’s debatable. For a quick rundown of IPv4 and IPv6 advantages and disadvantages, check our article right here. Even if the sixth version is the future, the Internet has grown fond of IPv4 and many companies choose to lease IPv4 blocks to help their businesses. Only time will tell which version shall prevail.

Where is IPv5 now?

Even if it never made it out of the experimental phase, IPv5 laid the ground for the technology that allows us to chat on platforms like Zoom, Google Meet, or Discord.

Before abandoning the protocol, engineers tested it thoroughly and came up with different backbones for it. IPv5 was tested on different operating systems and studied to see how it could improve audio and video streaming functionalities.

Even though it was left behind, IPv5 contributed to modern VoIP (voice over Internet Protocol) services and technologies. Without these tests, online audio and video chats would not be possible.

Will the saga continue? What comes after IPv6?

After experimenting with IPv1 to v3, engineers launched IPv4 for public users. Shortly after, they played with the Streaming Protocol and its second version. People used to refer to these two as IPv5 simply because they included Internet Protocol version 5 in their data packets.

During that time, the upgrade to IPv4 was around the corner. But to eliminate the confusion between that and the ST/ST2’s ‘nickname’, the engineers decided to jump straight to v6, so IPv6. As a result, IPV5 addresses never really happened.

This was not the end, however. Even if IPv6 seems to offer us nearly unlimited unique addresses, several sequels have also been in discussion for this franchise.

IP versions 7, 8, and 9 were also proposed. What happened to them? Versions 7 and 8 were moved to the Reserved (Historic) status, so they will not become publicly available. As for IPv9, well, that was an April Fool joke by IETF (Internet Engineering Task Force).  

So, anything about IPv10? Probably. According to a 2017 draft, it seems that v10 would enable smooth communication between IPv4 and IPv6. Thus, IPv10 would ensure compatibility between the two versions currently in use, but not come as a replacement.


Success is achieved through trial and error. That was what made the Internet one of mankind’s greatest achievements. Several IP versions were a failure, but their failure provided precious lessons that would pave the way for the modern online world.

IPv4 rose from the ashes of its predecessors. IPv6 was designed as an improvement. As for IPv5, it’s as mythical as it gets. It was never the official ”sequel” to IPv4. The fifth version was a protocol aimed at audio and video streaming.

While it never reached public users, this so-called IPv5 is the reason why we are able to exchange information on different VoIP platforms. 

By Carol Zafiriadi

According to the ancient texts, Carol has been passionate about IT and technology since his youth. He brought his experience and creativity to Pubconcierge as content writer, ready to both assimilate and share valuable information.

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