Redploying most of 127/8 as unicast public

Fri Nov 19 14:28:01 UTC 2021

This will break a significant number of existing deployments where people
have come to depend on a feature in Linux where any address within 127.0.0.0/8
can be “listened” and operate as a valid loopback address without configuring
the addresses individually as unicast on the interface.

In fact, this is true of any prefix assigned to the loopback interface, but 127.0.0.0/8
is automatic and difficult to change.

While I’m not sure this implementation in the Linux kernel was such a wonderful
idea, it is widely deployed and in use in a number of environments.

If we’re still using IPv4 widely enough that GUA space matters, we will have
far bigger problems than the lack of available GUA for it.

Owen

> On Nov 17, 2021, at 16:15 , William Herrin <bill at herrin.us> wrote:
> 
> On Wed, Nov 17, 2021 at 3:31 PM Jay R. Ashworth <jra at baylink.com> wrote:
>> This seems like a really bad idea to me; am I really the only one who noticed?
>> 
>> https://www.ietf.org/id/draft-schoen-intarea-unicast-127-00.html
> 
> Hi Jay,
> 
> I think it's a good idea. It won't be usable any time in the next two
> decades but if we're still using IPv4 in two decades we'll be glad to
> have anything we can scrounge. Why not ask OS authors to start
> assigning 127.0.0.1/16 to loopback instead of 127.0.0.1/8?
> 
> Regards,
> Bill Herrin
> 
> 
> -- 
> William Herrin
> bill at herrin.us
> https://bill.herrin.us/