billpg

(Short version: IPv6-only networks can provide a gateway for IPv4-only clients and advertise it via reverse DNS.)

SixGate has an interesting contrast with this RFC. RFC8950 removes IPv4 from the network core while preserving IPv4 reachability, whereas SixGate removes IPv4 from the service side while preserving reachability for IPv4-only clients.

In both cases, IPv4 survives as a compatibility layer rather than a fundamental requirement. The difference is that RFC8950 is aimed at network operators, while SixGate is aimed at the last remaining IPv4-only users.

In both cases, the goal is the same. Turn IPv4 from a requirement into an optional compatibility feature.

  Location: Daventry, UK
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You may know from my popular HN submissions...

  8086 Segmented Memory was a good idea. https://news.ycombinator.com/item?id=48619125
  The Road Not Taken: A World Where IPv4 Evolved. https://news.ycombinator.com/item?id=47352236
  Data-Mining Wikipedia for Fun and Profit. https://news.ycombinator.com/item?id=28234122

I've reviewed what I originally wrote and I prefer the text I published. Sure, I could review it all myself (indeed I used to) but that takes time and it was becoming a barrier to actually publishing stuff. Maybe I'd have got around to finishing it in a few months.

I don't use AI to write for me. I hate people who do that.

I get why hey didn't. Someone might want to run two processes each with its own segment, but the whole machine might only have 64k in total.

I did use an AI for spell-checking, punctuation, generally making it flow, but its all my text.

You think a machine is going to come up with "near pointers, far pointers, wherever-you-are pointers"?

(And I completely agree.)

But what should Intel have done? They needed a CPU that can run 8080 code but with more memory. Also it's the year ~1980 and we're limited to the technology of the age.

A system with 64k sized windows seems unavoidable.

If you extend the size of the address registers, 8080 code will only run in the first 64k, or require some kind of current window register.

An 8080 mode might have worked but that would have been expensive.

The key point is that POSIX does not actually define a real, physical epoch, and it explicitly avoids doing so. POSIX says every day is exactly 86400 seconds, leap seconds are ignored, the relationship between POSIX time and UTC is unspecified. In other words, POSIX defines how the "time()" API behaves, not what the underlying timeline is. It’s an OS level contract, not a timekeeping standard.

The problem I’m addressing is that POSIX retroactively assumes a form of UTC that didn’t exist in 1970–1971 and it provides no authoritative mapping between POSIX time and actual UTC. That’s why you can’t use POSIX as a normative reference for "seconds since 1970". It’s not a definition of time, it’s a behavioural model for system clocks.

This document is trying to define the actual timeline that people implicitly assume when they say "Unix timestamp", in a way that’s historically honest and citable. When I was looking at a number of RFCs that use these timestamps they didn't cite this reference, but went with the wooly "Number of seconds since 1970".

Values 0-127 are a single byte, but if that first byte has the continuation bit set, not only does that indicate the next byte has 7 more bits to contribute, it also moves the base up to the next window.

10000000 00000000 is the only way to represent 128.

10000000 10000000 00000000 is the only way to represent 16512.

Does this encoding have a name?

Switching on a machine that displays "9.8m/s²" isn't that much removed from looking it up in a book.

Old routers would be a normal UDP packet inside a normal IPv4 and route it normally. New routers would detect UDP port 84 and treat it as an extended IPv4x packet.

I took all that out because I wasn't writing a proposal for something we should actually implement in the real world, but an alternate history "What if people who wanted IPv4 but with extra space got their way" and the story was already too long.

Thanks though. Your comment really cheered me up.

ahem

https://owl.billpg.com/sixgate/

Your home router that sits on the end of a single IPv4 address would need to know about IPv4x, but in this parallel world you'd buy a router that does.

Note though that I'm not proposing IPv4x as something we should work towards now. Indeed, I come down on the side of being happy that we're in the IPv6 world instead of this alternative history.