Re: Redploying most of 127/8 as unicast public

[Joe Maimon <jmaimon () jmaimon com>]

Owen DeLong wrote:
> > On Nov 20, 2021, at 19:11 , Joe Maimon <jmaimon () jmaimon com> wrote:
> >
> >
> >
> > Owen DeLong wrote:
> > > I guess I don’t see the need/benefit for a dedicated loopback prefix in excess of one address. I’m not necessary 
> > > inherently opposed to designating one (which would be all that is required for IPv6 to have one, no software updates 
> > > would be necessary), but I’d need some additional convincing of its utility to support such a notion.
> > Since the loopback prefix in IPv4 is present and usable on all systems, IPv6 parity would require the same, so merely 
> > designating a prefix would only be the beginning.
> >
> > There may not be a need. But there is clearly some benefit.
> Which is? You still haven’t answered that question.

You have right below.

And if there is indeed no benefit, than there is no reason not to 
repurpose 127/8 considering that you may use many other ranges in IPv4 
for loopback and that you can just use IPv6 for loopback and there you 
go you have a whole /10.

Its not like it will overnight cause system admin headaches. And they 
should be running their loopback apps on IPv6 anyways.
> Well, technically, fe80::/10 is also present and predictable on every loopback interface. It does come with the 
> additional baggage of having to specify a scope id when referencing it, but that’s pretty minor.
>
>
> Nope… It’s every bit as deterministic as 127.0.0.0/8.
>
> If you send packets to fe80::*%lo0 on a linux box, they’ll get there. If you try it on something other than linux, it 
> probably doesn’t work.
> That’s also true of 127.*.*.*.

So fe80::/10 is the loopback prefix for IPv6


Joe