Redploying most of 127/8 as unicast public

Mon Nov 22 00:50:25 UTC 2021

> On Nov 20, 2021, at 20:37 , Joe Maimon <jmaimon at jmaimon.com> wrote:
> 
> 
> 
> Owen DeLong wrote:
>> 
>>> On Nov 20, 2021, at 19:11 , Joe Maimon <jmaimon at 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.

One doesn’t need a reason for inaction… One needs a reason to act. There is (so far) no compelling reason to repurpose 127/8 as far as I can see.

> Its not like it will overnight cause system admin headaches. And they should be running their loopback apps on IPv6 anyways.

You are arguing that just because we can do a thing, we should do a thing. I am arguing that unless there’s a compelling reason to change the standard, we should leave it as is until it dies a natural death of old age.
(or alternatively until we finally disconnect the life support keeping it artificially alive which is a more accurate metaphor for the current state of IPv4).

>> 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

It’s link local. It’s present on loopback. fe80::/10%lo0 (on a linux box) is a loopback prefix for IPv6 which is universally deployed.
The scope id becomes important in this context, but other than that, it’s identical to the semantics of IPv4.

Owen