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[IPv6]Re: New draft: "The IPv6 Loopback Address Prefix"

Brian E Carpenter <brian.e.carpenter@gmail.com> Wed, 03 December 2025 20:02 UTC

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Date: Thu, 04 Dec 2025 09:02:17 +1300
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To: Ole Trøan <otroan.ietf@gmail.com>
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From: Brian E Carpenter <brian.e.carpenter@gmail.com>
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Subject: [IPv6]Re: New draft: "The IPv6 Loopback Address Prefix"
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Hi Ole,

On 03-Dec-25 20:27, Ole Trøan wrote:
> Brian,
> 
>> On 3 Dec 2025, at 07:59, Brian E Carpenter <brian.e.carpenter@gmail.com> wrote:
>>
>> I don't think so. I think Bob's argument is just another version of "almost any address range would work for this purpose; it doesn't have to be special."
> 
> Doesn’t that depend on how we define loopback prefix behavior? I could not find that specified in either of the drafts.

Yes. That seems to be a problem.

> 
> The current loopback address is automatically plumbed into existing implementations.
> - any traffic destined to the loopback address will be sent to the node itself (ie up the host stack). Is that the behavior proposed for the loopback prefix? Without any address configuration any packet with a DA of loopback prefix is sent up the host stack?

Right. But it surely varies between operating systems and "what Linux does" is not a standard.

> - routers do not forward any packets with a loopback source. This is hard coded in forwarding paths.
> 
> How do the proponents of this idea intend for this to work? The suggestions of using an arbitrary prefix seems to imply people think no implementation changes are needed??

I think it assumes that (a) the code that people are talking about currently works for a particular IPv4 /8 prefix and for an IPv6 /128 prefix and (b) the code would work equally well for any IPv6 /96 prefix. I don't know if that's true.

    Brian

> Cheers,
> Ole

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