Source: IPv6—Theory, Protocol, and Practice, 2nd Edition by Peter Loshin (2004)


Some experts prefer to call IPv6 a revision or update or upgrade of IPv4, with the implication being that it is still IP no matter what version, and it still works the same way (more or less). That position is at best disingenuous. Version numbers to the contrary, IPv6 really is a different protocol from IPv4; it’s got a different address space, a different header format, a different set of rules on how to handle packets, and much more.

I'm not completely sure what exactly they're trying to say.


In software parlance, a version number is a number or set of numbers assigned to a specific release of a program. As the software is updated or improved by the manufacturer, new versions are released for download, and the version number increases to match this.

To give an example, the Safari browser I'm typing this response on is Version 10.0.1 (or v10.0.1) - if there was a minor update to the software, I'd expect the new version to be v10.0.2.

What this means for your example is that as the older protocol was referred to as IPv4 (or IP version 4), and the new version is named IPv6 (or IP version 6), one might expect that IPv6 is simply an update or improvement to the older IPv4. This actually isn't true - IPv6 is a completely different protocol, and can't be considered a simple update of IPv4. It should instead be considered as a protocol unto itself, doing many of the same tasks as IPv4, but constructed very differently.

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