[IPv6]Re: [v6ops] New draft: "The IPv6 Loopback Address Prefix"

[David Farmer <[e-mail]>]

While I'm not strongly opposed to this idea, I have always liked that the
IPv6 loopback address is a singular address rather than a prefix, as in
IPv4.

I don't think it is a major issue, and there are more than enough IPv6
addresses to define a lookback prefix for IPv6, instead of a singular
loopback address. It won't cause a shortage by any means.

I guess it is mostly a matter of taste. However, I would prefer a better
justification than simply saying we did it that way in IPv4, which seems to
be the primary justification.

Note that if we go hard with this idea, the entire IPv6 loopback prefix
should be added to the Locally-Served DNS Zones registry.

https://www.iana.org/assignments/locally-served-dns-zones/locally-served-dns-zones.xhtml#ipv6

Thanks.

On Tue, Nov 25, 2025 at 11:39 AM Warren Kumari <[e-mail]> wrote:

> Dear 6MAN and V6OPS,
>
> Geoff Huston and I have just submitted draft-kumari-ipv6-loopback - "The
> IPv6 Loopback Address Prefix"
> <https://datatracker.ietf.org/doc/draft-kumari-ipv6-loopback/>
>
> We believe that it is within the 6MAN charter ("The 6man working group is
> responsible for the maintenance, upkeep, and advancement of the IPv6
> protocol specifications and addressing architecture."), but I have CCed
> V6OPS as well, as it is clearly operational as well.
>
> Abstract:
> "This document updates the IP Version 6 Address Architecture to define the
> IPv6 address prefix ::/32 as the Loopback address prefix."
>
> Basically, this document expands the single loopback address ::1/128 into
> a prefix.
>
> Yes, we are aware that there have been some previous discussions[0] on the
> need (or lack thereof!) of a loopback prefix in IPv6, but we believe that
> they are worth revisiting.
>
> There are a number of situations in which having more than a single
> address is helpful; an obvious example of this is Dockers/k8s use of
> 127.0.0.11 for the DNS resolver, SPAM RBL use of the last octet on
> 127.0.0.x to encode the type of SPAM. It is also relatively common it use
> this for inter-service communication in container environments.
>
> It is also a common practice to bind different services to
> different addresses in the IPv4 loopback space to allow for scaling
> (avoiding the "Port already in use" issue), testing, etc.  Yes, these can
> be somewhat emulated with ULAs and / or additional interfaces and scopes,
> but they are all more complicated, and much more likely to result in
> leakage or collision.
>
> Another, more recent example is the ICANN Public Comment on "Name
> Collision IPv6 Research Study" and proposed use of ::ffff:7f00:3535 [1] -
> if there was a loopback prefix this would have been a better option[2]
>
>
> We expect a fairly robust discussion :-),
> W
>
> [0]: I know I've seen them, but I quick search of my mail was unable to
> find these — the authors are more than happy to link to previous documents,
> etc.
>
> [1]: See long threads on 6MAN
> https://mailarchive.ietf.org/arch/msg/ipv6/-HrYFMwHhsUWYxSXsFIkLpF_Qgk/ and
> V6OPS.
>
> [2]: Solving the technical concerns, but not necessarily the policy ones.
>
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