Not only because it is a proposed bridging solution between IPv4 and IPv6, the "version number" of IP is actually somewhat more like an identifier for subprotoc

Not only because it is a proposed bridging solution between IPv4 and IPv6, the "version number" of IP is actually somewhat more like an identifier for subprotocols. There is the list [1] of all taken version numbers managed by IANA. IPv4 is the version 4 because former versions of protocols (0 thru 3) are long obsolete; IPv6 is the version 6 because the version 5 was taken by another experimental protocol; and IPv10 ought to be the version 10 because the versions 6 thru 9 were used for proposed successors to IPv4 (and eventually the protocol of version 6 was chosen). I'm not very sure if other assignments were possible in the current standard process though (e.g. up to IPv14 would be available). [1] https://www.iana.org/assignments/version-numbers/version-numbers.xhtml https://www.iana.org/assignments/version-numbers/version-num...