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by billpg 91 days ago
No, in this hypothetical, routers that don't know about IPv4x will still route based on the top 32 bits of the address which is still in the same place for IPv4 packets. If your machine on your desk and the other machine across the internet both understand IPv4x, but no other machines in the middle do, you'll still get your packets across.
1 comments
kolinko 91 days ago
Well no, all the routers on your subnet need to understand it.

So let’s say your internet provider owns x.x.x.x, it receives a packet directed to you at x.x.x.x.y.y… , forwards it to your network, but your local router has old software and treats all packages to x.x.x.x.* as directed to it. You never receive any medssagea directly to you evem though your computer would recognise IPv4x.

It would be a clusterfuck.

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billpg 91 days ago
Your local machine isn't on the IPv4 internet if it doesn't have a globally routable IPv4 address.

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.

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zadikian 86 days ago
"all routers on your subnet need to understand that" I thought that meant the same thing you said
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kolinko 90 days ago
Of course you are, just behind NAT.

If your device has it's own public IPv4 address then you don't need IPv4x, IPv6 or whatever else.

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digitalPhonix 91 days ago
How would anything on the internet know about x.x.x.x.y.y…?

Your computer knows it’s connected to an old router because dhcp gave it x.x.x.x address and not x.x.x.x... so it knows it’s running in old v4 mode.

And it can still send outbound to a v4x address that it knows about.

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kolinko 90 days ago
> And it can still send outbound to a v4x address that it knows about.

No, it cannot, if there is a router on the way that is unaware of v4x, it will interrupt the signal.

Say your router is 1.2.3.4.0.0 in IPv4x (and 1.2.3.4 in IPv4). You are 1.2.3.4.0.1 . Someone sends you a message from outside. Your router only sees the previx of the address (1.2.3.4), and since it thinks it has 1.2.3.4, it reads the message and doesn't forward it further.

I highly recommend reading original TCP/IP RFC - it is a good tutotrial on how the IP routing works: https://datatracker.ietf.org/doc/html/rfc1180

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digitalPhonix 84 days ago
Your original comment was:

> but your local router has old software and treats all packages to x.x.x.x.* as directed to it.

So how do you have an IPv4x address? And then how did you let someone else on the internet know about the IPv4x address?

I know plenty well how IP routing works otherwise I wouldn't be in this conversation. Is there something specific in the RFC you think I’m not understanding?

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