Re: maximum ipv4 bgp prefix length of /24 ?

["Delong.com via NANOG" <nanog () nanog org>]

> On Oct 10, 2023, at 17:20, Mark Andrews <marka () isc org> wrote:
>
>
>
> > On 11 Oct 2023, at 09:43, Delong.com via NANOG <nanog () nanog org> wrote:
> >
> > > As a community, we have failed, because we never acknowledged and addressed the need for backward compatibility 
> > > between IPv6 and IPv4, and instead counted on magic handwaving about tipping points and transition dates where 
> > > suddenly there would be "enough" IPv6-connected resources that new networks wouldn't *need* IPv4 address space any 
> > > more.
> >
> > I’m not sure that we never acknowledged it, but we did fail to address it, largely because I think we basically 
> > determined that it’s “too hard”.
>
> It’s not actually that hard to do on a small scale, i.e. inside a home CPE with a DNS server and a NAT64 
> implementation that supports semi static mappings.  It does require IPv4 sites have IPv6 connectivity. You stand up a 
> DNS46 which requests an unused IPv4 address from a prefix block, say 10/8, when there is an IPv6 address without an 
> IPv4 address from the NAT64 with the IPv6 address it needs to be mapped to with an initial NAT64 lifetime value.  The 
> DNS46 would forget the mapping after half that initial lifetime.  The DNS46 would return A records limited half the 
> lifetime or less so they timeout before the NAT64 mapping expires.  The hard part is scaling up to a large client 
> base because not every DNS query results in IP traffic and you need a prefix block big enough to support the add rate 
> of the client base.  Doing this at ISP scale would be interesting to say the least.  This is not theoretical.  It has 
> been implemented in the past though some to the details might differ.

That’s not what we’re talking about… That’s translation, not backwards compatibility.

> Companies that have gone IPv6-only internally do this with fully static IPv4 to IPv6 mappings and skip the DNS46 step.

But doing that requires that the companies have a certain amount of V4. The question was how to talk to v4-only hosts 
with ZERO IPv4 addresses available to you.

> So if you have a legacy device that can’t talk IPv6 there is a solution space that allows it to talk to the IPv6 
> internet.  You need to install it however.  Adding DNS46 to a nameserver is about a days if you already have a DNS64 
> model.  The hard bit is working out how to talk to the NAT64 implementation.  A good project to put on a Raspberry Pi 
> or similar.

I’m a new entity. I need to talk to the IPv4 internet. I have zero IPv4 addresses and none are available to me.

How do I make any of this work?

That’s the question that remains unsolved and that’s the one we most desperately failed to tackle.

Owen