Re: Redploying most of 127/8 as unicast public

[Joe Maimon <jmaimon () jmaimon com>]

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.

> > I can understand that sometimes you may explicitly not want to use the loopback prefix for loopback applications. In 
> > fact many times. However, you dont really have much options when it comes to IPv6
> I have not encountered a device where I could not assign additional prefixes to a loopback interface in IPv6, so I’m 
> having trouble understanding your meaning here.

In IPv6 if you want a loopback prefix you have to pick one yourself or 
determine which one the system has chosen on its own. Because there is 
no dedicated loopback prefix other than ::1/128

> > Anyone who wants to assign routable IPv4 to loopback is free to do so and there are plenty of IPv4 ranges to choose 
> > from.
> >
> > The converse is not true in IPv6.
> I guess that depends on what you mean by “converse”.

I mean that in IPv6 you must assign an otherwise non-loopback prefix if 
you want one.

> If you mean non-routable addresses deployed on the loopback interface, I think LL works fine for that purpose.

It works, but it is non deterministic and system dependent.
> If you mean routable addresses deployed on the loopback interface, I think ULA or GUA works fine for that purpose.

And IPv4 has that too.
> > I actually think that IPv6 evangelicals should welcome any all ideas like this, especially if they believe it will 
> > further degrade the overall state of IPv4, because that should only serve as stronger impetus for IPv6 deployment. That 
> > mode of thought has been commonly expressed here and other places before.
> I don’t think the current proposals being discussed will improve or degrade IPv4. I think they will distract 
> implementors that choose to implement them from useful work for a while and end in neither benefit nor detriment beyond 
> the detriment that comes from wasting effort.

There seems to be some weird mental representation of how standards 
affect the real world. Standards do not demand or direct or control in 
any way what individuals do based upon their own assessment of their 
needs, available resources and resulting benefits.

You are neither responsible or in control of how people choose to expend 
their implementing resources. Nor should you.

What standards do is increase the potential benefits of conforming to 
certain behavior.

So what you are really saying is that standardizing something that 
others may then choose to recognize as a worthwhile expenditure of their 
resources is something you would like to prevent on the assumption that 
those efforts would have otherwise gone into IPv6 advancement.

You dont have the immediate moral high ground on that one.

You dont have the long term moral high ground on that one because such 
thinking isnt new and we know its wishful at best.

You dont have the logical high ground on that one because you are 
assuming facts not in evidence, namely that

- Resources are being feverishly expended deploying IPv6 (as if)

- Those same resources will be the ones redirected to implement ideas 
such as these

- That those efforts are in anyways comparable in scope to work being 
done on IPv6 (which is supposed to be done already)

- That any such diversion of activity will actually have any real world 
affect on the state of IPv6


> If I thought it would significantly degrade IPv4, I might be all for it, but I doubt it would even be that useful.
>
> Owen

Reclaiming 127/8 while assigning a /64 for loopback in IPv6 would create 
a clear (but narrow) case where IPv6 would be superior to IPv4, 
irrelevant of overall network state.

Objectors to the proposal based upon their real world use of far larger 
than v4 /16 for loopback applications could implement on IPv6 with even 
more space, and in the exact same addressing context.

Which GUA and LL are not, no matter how readily available and easily 
assignable and otherwise equivalent they are in every way but the one. 
They are not loopback designated by standard (and system implementation).

Joe