As all of us know that after IPv4 it came IPv6. How this transition happened?
I just want to know was there any IPv5 also? or there is any other logic in naming this version of IP as IPv6?
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The second version (of Internet Stream Protocol), known variously as ST-II or ST2, distinguishes its own packets with an Internet Protocol version number 5, although it was never known as IPv5.
The Internet Stream Protocol family was never introduced for public use, but many of the concepts available in ST are similar to later Asynchronous Transfer Mode protocols and can be found in Multiprotocol Label Switching (MPLS). They also presaged Voice over IP.
The version numbers for the 'version' are part of the IP header field (described in RFC 791) and is 4 bits wide. As with many of the numbers that find their way into the internet, the numbers for the version are part of the Internet Assigned Numbers Authority.
The list of the version numbers can be found at http://www.iana.org/assignments/version-numbers/version-numbers.xhtml which shows:
0 Reserved https://www.rfc-editor.org/rfc/rfc4928 section 3 1 Reserved https://www.rfc-editor.org/rfc/rfc4928 section 3 2 Unassigned 3 Unassigned 4 IP - Internet Protocol https://www.rfc-editor.org/rfc/rfc791 5 ST - ST Datagram Mode https://www.rfc-editor.org/rfc/rfc1190 6 IPv6 - Internet Protocol version 6 https://www.rfc-editor.org/rfc/rfc1752 7 TP/IX - TP/IX: The Next Internet https://www.rfc-editor.org/rfc/rfc1475 8 PiP - The P Internet Protocol https://www.rfc-editor.org/rfc/rfc1621 9 TUBA - TUBA https://www.rfc-editor.org/rfc/rfc1347 10 Unassigned 11 Unassigned 12 Unassigned 13 Unassigned 14 Unassigned 15 Reserved
And this is where the numbers come from and whats already out there. If there is something after IPv6 that is not one of the already defined numbers, the next available internet protocol version number available is 10.
Note that these assigned numbers were from days back when things were a bit more... care free with the internet. Classful network /8 blocks were given out fairly freely (known as 'class A' networks) - a number of universities have network spaces of millions (16.7M) of IPv4 addresses.
Allocating versions numbers to experimental protocols was probably also a sign of the times (though IPv6 has made it to practical use). IANA is much more conservative with assigning numbers today.
"So what happened to IPv5? IPv5 was used to define an experimental real-time streaming protocol. To avoid any confusion, it was decided to not use IPv5 and name the new IP protocol IPv6. " (Cisco CCNA Exploration Courses - Accessing the WAN)
Here's a link! @ Hemant You will find there enhancements that IPv6 offers.