
Why can't we just prefix IPv4 - neilellis
Instead of the complexity of switching to IPv6 couldn&#x27;t we have a an IPV4.1 that supports variable length addresses with 0 indicating legacy.<p>So:<p>0.192.168.0.1 -&gt; 192.168.0.1<p>0.0.0.192.168.0.1 -&gt; 192.168.0.1<p>25.192.168.0.1 -&gt; new address space 25 with IP of 25.192.168.0.1<p>25.100.1.2.3.4 -&gt; new address space 25.100... with IP of 25.100.1.2.3.4<p>then the CIDR notation would just become:<p>25.192.168.0.1&#x2F;32 for 25.192.168.0.0 -&gt;25.192.168.0.255<p>Router&#x27;s could use the x.y.z.0.0.0.1 address as gateways by default, making routing easy.<p>Under the covers it would be possible to use IPv6 as the protocol like 6to4 (https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;6to4) but with variable sized addressing from a consumer&#x27;s perspective.<p>Just a thought.
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Piskvorrr
There was a longer article on this, linked a few weeks back (actually written
in 2002).

TL;DR: this would work, except for a completely minor issue: a large-scale
HW+SW overhaul of _everything_ up and down the net stack would be necessary
before this extension would work (just as with IPv6). Therefore, no
significant benefit over IPv6 (plus a bunch of brand new, IPv4.1 specific
problems).

[https://blog.sesse.net/blog/tech/2016-01-06-20-54_ipv6_non_a...](https://blog.sesse.net/blog/tech/2016-01-06-20-54_ipv6_non_alternatives_djbs_article_13_years_later.html)

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detaro
What would that make easier? You still need new networking stacks, have to
redefine all protocols carrying IPs to allow for those, legacy hosts still
can't use it, ...

\+ Networking really doesn't like headers of varying length if avoidable,
because it makes fast parsing (esp in hardware) harder.

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neilellis
That's a very good point. So here's an idea. Use the scheme I mentioned from a
user point of view but translate to IPv6 as a transport protocol (since we're
tunneling 6 over 4 at the moment this is not impossible).

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Piskvorrr
So, IPv4 over IPv4.1 over IPv6? What good is the middle step?

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justinsb
"Legacy" IPs would have no way to access "new" IPs; they have no way to
differentiate "0.192.168.0.1" from "1.192.168.0.1"

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neilellis
You'd need translation on router's of course because without upgrades they
wouldn't understand the variable sized address space - but since I'm seeing
people route IPv4 over IPv6 it's not completely insane.

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Piskvorrr
You'd need translations _everywhere_ \- you couldn't just "let the router
decide", the end nodes would need to support this as well.

( Let's say we had IPvIII, consisting of just three bytes per address: 10.1.2
- and now we went from that to 10.1.2/24, i.e. 10.1.2.0-255. How does the
router to know that an IPvIII client is requesting 10.1.2.15 ? It doesn't. The
extension from IPv4 to IPv4+ is equivalent.)

