Re: [v6ops] Scope of Unique Local IPv6 Unicast Addresses (Fwd: New Version Notification for draft-gont-6man-ipv6-ula-scope-00.txt)

[Mark Smith <[e-mail]>]

On Sun, 21 Feb 2021 at 20:39, Fernando Gont <[e-mail]> wrote:
>
> Hi, Mark,
>
> On 20/2/21 18:54, Mark Smith wrote:
> > On Fri, 19 Feb 2021 at 14:22, Fernando Gont <[e-mail]> wrote:
> >>
> >> On 18/2/21 22:21, Mark Smith wrote:
> >>>
> >>>
> >>> On Fri, 19 Feb 2021, 11:37 Brian E Carpenter,
> >>> <[e-mail] <mailto:[e-mail]>> wrote:
> >>>
> >>>      So, my thought (and it belongs on this thread OR the 'IPv6
> >>>      addressing: Gaps?' one) is something like:
> >>>
> >>>      We should abolish, delete, expunge and deprecate the word "scope"
> >>>      from all IPv6 documents. It clearly doesn't have an agreed meaning,
> >>>      so it is worse than useless.
> >>>
> >>>
> >>> I think the word scope is fine.
> >>>
> >>> The problem is that by itself it doesn't specify what thing the scope is
> >>> applying to, and people aren't explicitly saying what that scope they're
> >>> referring to. "Global scope" - scope of what?
> >>
> >> As per RFC4007, scope refers to address uniqueness.
> >
> > RFC4007 doesn't apply to ULAs:
> >
> > "Though the current address architecture specification [1] defines
> > unicast site-local addresses, the IPv6 working group decided to
> > deprecate the syntax and the usage [5] and is now investigating other
> > forms of local IPv6 addressing.  The usage of any new forms of
> > local addresses will be documented elsewhere in the future.  Thus,
> > this document intentionally focuses on link-local and multicast
> > scopes only."
> >
> > RFC4193 is of course this future document.
>
> RFC4007 is an architecture document and does not talk about ULAs because
> it *predates* ULAs.
>
> Given that RFC4007 is an architectural document, it is mean to apply to
> all developments -- unless updated.
>
>

Did you miss this?

"Thus, this document intentionally focuses on link-local and multicast
scopes only.""



>
>
>
> >>> ULAs (and addresses in general) have at least two different scopes:
> >>>
> >>> - scope or domain of intended uniqueness
> >>
> >> For ULAs, this is "set of interconnected ULA-based networks" -- i.e.,
> >> some sort of limited domain/scope.
> >>
> >
> > RFC4193 explicitly says that the scope of uniqueness is global:
> >
> > "Local IPv6 unicast addresses have the following characteristics:
> >
> >        - Globally unique prefix (with high probability of uniqueness)."
>
> Probability != certainty
>
>     [RFC4007] defines the scope of an address as:
>
>        "[the] topological span within which the address may be used as a
>        unique identifier for an interface or set of interfaces"
>
>     And defines the "global scope" to be used for:
>
>        "uniquely identifying interfaces anywhere in the Internet"
>
>
>
> It does *not* say "probably uniquely identifying interfaces anywhere in
> the Internet"
>
>
>
>
> >>> - scope or domain of intended forwarding within a network or across a
> >>> set of networks
> >>
> >> In this case, same as before.
> >>
> >> Normally, both of these are equal:
> >
> > In ULAs they aren't.
>
> If you look at the definition of global scope from RFC4007, the
> definition of ULAs as being global scope doesn't match with such definition.
>
>
> > Link-Local addresses generated using RFC7271s aren't either.
>
> That's not correct. RFC7217 leads to a unique address, or fails. ONece
> you have successfully generated the address, the address does uniquely
> identify an interface on the local-link.
>
>
>
> > The IID is likely to be globally unique, even though the Link-Local
> > prefix isn't. Combining the globally unique IID with the Link-Local
>
> IIDs are *not* globally unique. They are *locally* -- you check for
> uniqueness on the local link (via DAD), but not globally.
>
>
>
> > prefix results in a globally unique Link-Local address - the
> > forwarding scope of the packets with those addresses is limited to a
> > link, however the RFC7217 LL address's scope of uniqueness is global.
>
> Not sure what you mean: link-local addresses, as the name imply, have a
> link-local scope.
>
>
>
>
> > and address uniqueness will limit
> >> reachability.
> >>
> >
> > I'm not sure I understand what you're saying.
>
> You can only employ an address where the address is meaningful.
> "Meaningful" means that the address specifies the same interface at the
> sender as well as at the receiver. And it is the "scope" property which
> specifies the topologicaly span where the address complies with that
> property.
>
>
> Obviously, the address scope will be the upper constrain on
> reachability, because you can certainly *not* reach what you cannot address.
>
> (you cannot get to a place if you cannot specify where you want to go)
>
>
>
> > I am wondering if my definition of "reachability" is different from
> > yours. I see it as describing the likely current forwarding capability
> > of the network, because the main use of the term I've encountered is
> > in the context of BGP.
>
> Reachability: topological span where a packet with said address could
> possibly be forwarded to.
>
>
>
> > So the "forwarding domain" is what is designed to be the case, whereas
> > actual reachability depends on route tables, paths and links being
> > available, ACLs or other security policies etc, intentional or not
> > duplicate addresses (i.e. anycast).
>
> The above would apply.
>
> Thanks,
> --
> Fernando Gont
> SI6 Networks
> e-mail: [e-mail]
> PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492
>
>
>
>