--- gert@space.net wrote: From: Gert Doering gert@space.net To: Scott Weeks surfer@mauigateway.com On Sun, Oct 29, 2017 at 02:53:41PM -0700, Scott Weeks wrote:

I was not around for those discussions (and not being a computer science person, nor wanting to go on this for too long as has been endlessly done on other lists), but it seems TLV would have allowed 4 to be a subset of the new space. I never heard that discussed much and that's what I meant by my comment.

The point is: if you introduce a change to the packet format (and TLV would be), you are no longer compatible with IPv4. Which makes the whole "I want this to be compatible so I do not have to change infra or end points" totally moot.

Worse, then you have "old IPv4" and "new IPv4" machines who might or might not be able to talk to each other, depending on which IPv4 address the "new IPv4" got (a long one or a short one) - while with IPv6, you have unmodified old IPv4 to ensure compatibility during the transition, and then you turn it off (in 10 years or so). ---------------------------------------------------

I guess all ways IETF participants thought of a new address space would not have allowed backwards compatibility with IPv4?

Thanks for the explanation. I appreciate it. Hopefully, others here find it interesting, too.

scott