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

[Sebastian Moeller <[e-mail]>]

> On 3. Dec 2025, at 07:58, Brian E Carpenter <[e-mail]> wrote:
> 
> On 03-Dec-25 19:04, Sebastian Moeller wrote:
>> Respectfully,
>> You seem to be arguing for even more operational differences between 4 and 6 here.
> 
> 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."
> 
> The main difference from IPv4 is that we have plenty of address ranges we could choose. And of course in both cases we can invent as many virtual interfaces as we need.

[SM] Yes, we can, but the consequence is further divergence between v4 and v6...

> 
>> No matter how backward we consider v4 to be, this would introduce additional friction for uses having the pleasure having to deal with both v4 and v6, is that really worth it?
> 
> What's the friction?

[SM] That to achieve the same goal two different mental models need to be maintained and two different conceptual address ranges need to to be selected.

> Once you picked (say) a /96 to use, the algorithm would be identical, wouldn't it, apart from a longer prefix?

[SM] The algorithm doers not care, I am concerned about the humans that would want to configure this... at least for me "pick addresses in the same subnet as home" is simpler and easier not to mix up than use 127.0.0.0/24 (or whatever) for v4 but 2001::/32 (or whatever) for v6. Is this ability heavy lift? No, but these kind of not strictly necessary divergences add up. Now, if we would be close to sun-set and retire v4 that might be a decent strategy, but my personal take is we are not even close so I at least want to mention the "friction" component, even if it might not carry the day. (While I would like unity between the IPs here, this is not a strong feeling)

Regards
	Sebastian

> 
>   Brian
> 
>> On December 2, 2025 6:52:01 PM GMT+01:00, Bob Hinden <[e-mail]> wrote:
>>    Warren,
>>    Two thoughts.
>>    Chair hat on: I agree that this should belong to 6MAN.
>>    Individual hat on: The question I have is about using loopback addresses for virtual host addresses. What was done with in IPv4 always seems to me like a “hack”. Probably because of IPv4 limitations. We don’t have these limitations in IPv6 and I wonder if that is the right to replicate what was done in IPv4 in IPv6.
>>    We could leave the IPv6 loop back address alone (that is, use it for loopback), and define a new set of IPv6 virtual host addresses. It doesn’t seem to me that it has anything to do with a loopback function.
>>    Further, there are a lot of possibilities for what to use for this, especially given the trend to allocate a prefix to a host. Even without that an IPv6 node can have many addresses.
>>    Bob
>>        On Dec 1, 2025, at 12:02 PM, Warren Kumari <[e-mail]> wrote:
>>        [ - V6OPS, +6MAN Chairs ]
>>        Dear 6MAN chairs,
>>        The authors would like to request adoption of this document.
>>        It is clear that there is still work needed before the document is ready
>>        for publication, but it's also clear that there is significant interest in
>>        the topic.
>>        It would be helpful for the document to have a designated home - I had
>>        originally CCed V6OPS, and there has been significant discussion there too.
>>    ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>>    IETF IPv6 working group mailing list
>>    [e-mail]
>>    List Info: https://mailman3.ietf.org/mailman3/lists/[e-mail]/ <https://mailman3.ietf.org/mailman3/lists/[e-mail]/>
>>    ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>> -- 
>> Sent from my Android device with K-9 Mail. Please excuse my brevity.
>> --------------------------------------------------------------------
>> IETF IPv6 working group mailing list
>> [e-mail]
>> List Info: https://mailman3.ietf.org/mailman3/lists/[e-mail]/
>> --------------------------------------------------------------------
> --------------------------------------------------------------------
> IETF IPv6 working group mailing list
> [e-mail]
> List Info: https://mailman3.ietf.org/mailman3/lists/[e-mail]/
> --------------------------------------------------------------------