Re: [v6ops] What's "global"? -- Re: Possible issue with source address selection for ULAs...

[George Michaelson <[e-mail]>]

Forgive a probably obvious corollary/comment:

"globally reachable" doesn't mean it IS routed. It means it COULD BE.
Nobody should have bit marker rules to deny its routability, whereas
the others could have "don't route me bro" qualities by their bitmark
(multicast aside)

On Thu, Jan 13, 2022 at 11:11 AM Brian E Carpenter
<[e-mail]> wrote:
>
> Ted,
>
> We have IETF rough consensus for the text in RFC8190/BCP153:
>
> "  Globally Reachable - A boolean value indicating whether an IP
>     datagram whose destination address is drawn from the allocated
>     special-purpose address block is forwardable beyond a specified
>     administrative domain."
>
> and we have IETF rough consensus for the text in RFC4291 (PS):
>
> "
>     The type of an IPv6 address is identified by the high-order bits of
>     the address, as follows:
>
>        Address type         Binary prefix        IPv6 notation   Section
>        ------------         -------------        -------------   -------
>        Unspecified          00...0  (128 bits)   ::/128          2.5.2
>        Loopback             00...1  (128 bits)   ::1/128         2.5.3
>        Multicast            11111111             FF00::/8        2.7
>        Link-Local unicast   1111111010           FE80::/10       2.5.6
>        Global Unicast       (everything else)
> "
>
> Perhaps surprisingly, uniqueness is not defined as a required
> property of a Global Unicast address in that RFC. In practice,
> because of ULAs or any other kind of limit on forwarding, the
> practical implication of the "Global Unicast" property is "this
> address MAY be forwarded off link and its prefix MAY be the
> subject of a routing protocol."
>
> Nothing more, so ULAs are simply a subset of Global Unicast,
> routable but not globally reachable.
>
> Regards
>     Brian Carpenter
>
> On 13-Jan-22 07:20, Ted Lemon wrote:
> > I don't think there's strong agreement on this, actually. We've had discussions about it before (maybe not here?). What I think "global scope" means is that the identifier is presumed to be globally unique. It doesn't
> mean that the identifier /is/ globally unique: just that we expect to be able to treat it as it is. I think that this is pretty close to what you said, but just thinking about it from a different angle.
> >
> > On Wed, Jan 12, 2022 at 1:04 PM Fred Baker <[e-mail] <mailto:[e-mail]>> wrote:
> >
> >     Please correct my understanding.
> >
> >     My understanding of "global scope" is that one could imagine the address being reachable from a non-local site, such as a site the the UAL owner/user has an agreement with, while "globally reachable" is a statement about routing and may or may not be true of any address that isn't local in scope. Close?
> >
> >      > On Jan 5, 2022, at 1:08 PM, Brian E Carpenter <[e-mail] <mailto:[e-mail]>> wrote:
> >      >
> >      > On 06-Jan-22 09:12, Gábor LENCSE wrote:
> >      >> 1/5/2022 8:51 PM keltezéssel, Brian E Carpenter írta:
> >      >>>> If I can avoid using ULA, I would always do that.
> >      >>>
> >      >>> All the same, it seems that we really need a document that
> >      >>> characterises use cases for ULA usage and suggests guidelines.
> >      >>> We've tried and failed to do that it in the past, so the
> >      >>> issue keeps coming up.
> >      >>>
> >      >> Did you mean this one?
> >      >> https://tools.ietf.org/id/draft-carpenter-6man-whats-global-00.txt <https://tools.ietf.org/id/draft-carpenter-6man-whats-global-00.txt>
> >      >> I am not sure, what the best fix could be, but I think it would
> be worth
> >      >> trying to find one. :-)
> >      >
> >      >
> >      > No, I meant the previous serious attempt:
> >      > https://datatracker.ietf.org/doc/draft-ietf-v6ops-ula-usage-considerations/ <https://datatracker.ietf.org/doc/draft-ietf-v6ops-ula-usage-considerations/>
> >      > but since we never reached WG consensus on that, a different approach seems
> >      > to be needed.
> >      >
> >      > The "what's global?" issue was formally resolved by RFC8190 (part of BCP153). This fixed the IANA terminology to use "globally reachable"
> at https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml <https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml>. But the problem isn't resolved in the real world: for example the Python ipaddress library is still wrong, since it doesn't distinguish "global scope" (should be True for ULAs) from "globally reachable" (should be False for ULAs).
> >      >
> >      >   Brian
> >      >
> >      >> Gábor
> >      >>> Regards
> >      >>>    Brian
> >      >> _______________________________________________
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> >      >
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