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Re: [OT] IP address collisions (was: Accessing a host with variable IP addresses / connection types)

On Wed, Apr 17, 2019 at 08:06:05PM -0000, Curt wrote:
On 2019-04-17, Pascal Hambourg <pascal@xxxxxxxxxxxxxxx> wrote:
Le 17/04/2019 à 18:42, Michael Stone a écrit :
On Wed, Apr 17, 2019 at 12:38:11PM -0400, Celejar wrote:
On Wed, 17 Apr 2019 12:10:56 -0400 Michael Stone <mstone@xxxxxxxxxx>

On Wed, Apr 17, 2019 at 11:57:43AM -0400, Celejar wrote:
>I was rather shocked to see that there was no definitive solution to
>avoid address collisions

Sure there is--globally unique IPs.

I assume you're referring to IPv6? I was referring to IPv4.

It applies to both, though we've run out of IPv4. There's no other way
to guarantee the absence of network collisions.

A properly generated IPv6 ULA (Unique Local Address) prefix is unlikely
to have collisions.

I thought that was exactly what he was saying.

No, the ULA is the IPv6 equivalent of RFC1918 space--you can use it internally without central registration by choosing a subnet from fd00::/8. The space is so much larger that it's much less likely that two sites would pick the same prefix, but there are no guarantees.