[digitalPhonix]

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.

[kolinko]

> 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

[digitalPhonix]

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?