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

David Farmer <farmer@umn.edu> Wed, 26 November 2025 01:29 UTC

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From: David Farmer <farmer@umn.edu>
Date: Tue, 25 Nov 2025 19:29:19 -0600
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To: Geoff Huston <gih902@gmail.com>
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Subject: [IPv6]Re: [v6ops] Re: Re: New draft: "The IPv6 Loopback Address Prefix"
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Geoff,

To clarify, I don't object to 4B loopback addresses, or possibly even more.
My concern was corner cases regarding the reuse of IPv4-Compatible IPv6
Addresses. Even if something was still using them, it seems unlikely that
::0/104 or the equivalent of 0.0.0.0/8 would cause any problems. However, I
accept your argument that it's been long enough. Other than ::ffff:0:0/96
being used by IPv4-Mapped IPv6 Address, I would not object to using ::0/48
or even ::0/32. Nevertheless, you make a good point about Mark's proposed
use case.

Thanks.

On Tue, Nov 25, 2025 at 6:49 PM Geoff Huston <gih902@gmail.com> wrote:

> Hi Mark,
>
> I hear you, but I also observe that a prior effort to expand this
> designation
> in 2013 did not get beyoind a draft. This incarnation of the proposal is
> deliberately
> more modest (even then I see David Farmer saying (paraphrased) "whoa! Way
> too much!" So we have one comment saying "too big" and another saying "too
> small"!
>
>
> I'm inclined to say that the draft will keep this proposal  at a /96 for
> now but
> doubtless Warren and I will keep a close eye on any other comments
> that have a view about the appropriate size for a loopback prefix.
>
> But I do note:  "Those loopback interface addresses were all announced into
> the routing protocol" might bne interpreted as a bit contrary to RFC 4291
> which says quite  definitively "keep loopback em to yourself" So I am not
> exactly on board with a rationale that relates to a use scenario in routing
> protocol that "exports" these addresses out to neighbours, if I interpret
> your
> description correctly.
>
> regards,
>
>   Geoff
>
>
> _______________________________________________
> v6ops mailing list -- v6ops@ietf.org
> To unsubscribe send an email to v6ops-leave@ietf.org
>


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David Farmer               Email:farmer@umn.edu
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