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

From: "Templin (US), Fred L" <[email-masked]>
Date: Thu, 18 Feb 2021 20:11:18 +0000

Fernando,

Then, let's have a scope for "MANET-local" scope which is what you get when
you have a small collection of (probably) mobile nodes that form a network
between themselves without the support of any infrastructure. I think HITs
would make for fine IPv6 addresses within the MANET-local scope, but if the
MANET ever connects to the global Internet then nodes will also want to get
a *real* GUA (served by the infrastructure) to go along with the HIT they
already have.

Did I mention HITs are self-generated, and not delegated by some
infrastructure node?

Fred

> -----Original Message-----
> From: Fernando Gont [mailto:[email-masked]]
> Sent: Thursday, February 18, 2021 11:53 AM
> To: Templin (US), Fred L <[email-masked]>; IPv6 Operations <[email-masked]>; [email-masked]
> Subject: Re: [v6ops] Scope of Unique Local IPv6 Unicast Addresses (Fwd: New Version Notification for draft-gont-6man-
> ipv6-ula-scope-00.txt)
> 
> 
> On 18/2/21 16:46, Templin (US), Fred L wrote:
> [...]
> >>
> >> Hi, Fred,
> >>
> >> On 18/2/21 16:11, Templin (US), Fred L wrote:
> >> [...]
> >>>> On 18/2/21 14:37, Templin (US), Fred L wrote:
> >>>>> Another aspect I failed to mention is that the use of (H)HITs does not
> >>>>> necessarily  mean that all aspects of the HIP protocol must be used. (H)HITs could be
> >>>>> used with the AERO/OMNI services instead, for example.
> >>>>
> >>>> Questions: Are these addresses globally-unique?
> >>>
> >>> Yes - global uniqueness is a key objective of (H)HIT. Aggregation is not within
> >>> scope, however.
> >>
> >> If that's the case, then, according to RFC4007, they are global addresses.
> >
> > I actually think HITs are a bit of a gray area. According to RFC7343, they are
> > formed from the GUA prefix 2001:20::/28 but the remaining bits following
> > the ::/28 prefix are cryptographically generated and hence non-aggregatable.
> 
> BUt according to RFC4007, the scope is defined by the topological span
> where the address is meaningful....
> 
> 
> > That means that there is no way to represent a group of them in the routing
> > system using any other prefix length than /128.
> 
> That's not a requirement when it comes to "scope".
> 
> 
> 
> >> (I'd argue that if they cannot be aggregated, that's because they
> >> resulting "addresses" are not really topologically-dependent, in which
> >> case you might probably argue that they are not addresses in the first
> >> place :-) )
> >
> > Not in terms of routing across the global Internet, no, because it would not
> > scale to inject large numbers of /128's into the global Internet routing system.
> 
> The thing is that if they don't represent a location in the network
> topology, they don't seem to qualify as an address, anyway.
> 
> An address is supposed to be a topologically-dependent identifier --
> i.e., to convey information of location ("where?").
> 
> Thanks,
> --
> Fernando Gont
> SI6 Networks
> e-mail: [email-masked]
> PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492
> 
> 
>

---

From: Brian E Carpenter <[email-masked]>
Date: Fri, 19 Feb 2021 09:26:50 +1300

> Did I mention HITs are self-generated, and not delegated by some

Therefore, presumably, they are only statistically unique, even though
there are 100 pseudo-random bits. ULAs on steroids.

   Brian

> --------------------------------------------------------------------
> IETF IPv6 working group mailing list
> [email-masked]
> Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6
> --------------------------------------------------------------------
>

---

From: David Farmer <[email-masked]>
Date: Thu, 18 Feb 2021 16:52:04 -0600

So let's be clear "IPv6 Address Scope" does not really have the general
meaning of the word "scope", it has a very specific meaning that in my
opinion boils down to are Zone Indexes or Identifiers needed to
uniquely identify them.

There is an argument to be made that ULAs should be Scoped, and if they
were globally reachable they would have to be Scoped. Nevertheless, they
are not globally reachable, and therefore so while it is possible that
there is another user of the same ULA prefix you are using. But, if you
follow the algorithm, in RFC4193 for allocation, the probability of that
duplicate user ever being reachable by you is very-very small.

So then do you want to use Zone Indexes or Identifiers with MANET? I doubt
it, personally, I believe that would effectively make MANET unusable by
most users.

Thanks

On Thu, Feb 18, 2021 at 2:11 PM Templin (US), Fred L <
[email-masked]> wrote:

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

-- 
===============================================
David Farmer               Email:[email-masked]
Networking & Telecommunication Services
Office of Information Technology
University of Minnesota
2218 University Ave SE        Phone: 612-626-0815
Minneapolis, MN 55414-3029   Cell: 612-812-9952
===============================================

---

From: Fernando Gont <[email-masked]>
Date: Thu, 18 Feb 2021 20:10:05 -0300

> opinion boils down to are Zone Indexes or Identifiers needed to 

Well, this is a spec inconsistency. You have one spec (RFC4007) defining 
"scope" and "global scope", and another specs:

a) making use of the same terms in an incorrect way, or,

b) employing same terms but with a different definition.

i.e., either the definition in RFC4007 is incorrect, or the use in 
RFC4193 and implicit use in RFC4291 is incorrect.

As you've correctly noted, this applies to other address types, too.

> were globally reachable they would have to be Scoped.

Well, you can also argue that they are not globally reachable because 
they are actually scoped ;-)

> Nevertheless, they 

This accounts for "why do things do not break in practice". But 
certainly doesn't help with the consistency of the specs.

Thanks,

---

From: "Manfredi (US), Albert E" <[email-masked]>
Date: Thu, 18 Feb 2021 23:39:02 +0000

-----Original Message-----
From: ipv6 <[email-masked]> On Behalf Of Fernando Gont

You can also argue, if there are prefix bits sent in the clear, and those prefix bits are used to send the packets to a pre-determined gateway, and that gateway is then used to decrypt all of the remaining address bits, then route packets through a walled garden intranet with global span, then global scope could still apply.

Just sayin'. These still aren't like RFC 1918.

Bert

---

From: David Farmer <[email-masked]>
Date: Thu, 18 Feb 2021 17:41:27 -0600

> certainly doesn't help with the consistency of the specs.

I agree there are inconsistencies, how fatal those inconsistencies are, I
think we disagree. I believe adding a single word to the definition in
RFC4007 will align RFC4007 and RFC4193,  "uniquely identifying interfaces
anywhere *reachable* on the Internet".

Further, I think when we eventually get around to revising RFC4291, every
remaining use of the word "scope" needs to be examined, and probably a
reference to the updated definition in RFC4007 or its replacement should be
added. Note most of the words "scope" in RFC4291 are in reference to local
and global IIDs, which basically go away with RFC7136. But even after that
cleanup, I think there is some confusion around "scope" and its meaning, at
least for the uninitiated reader of RFC4291.

Thanks

---

From: Fernando Gont <[email-masked]>
Date: Thu, 18 Feb 2021 21:09:37 -0300

On 18/2/21 20:41, David Farmer wrote:
> 
> 
> On Thu, Feb 18, 2021 at 5:10 PM Fernando Gont <[email-masked] 
> <mailto:[email-masked]>> wrote:
> 
[...]
> 
> I agree there are inconsistencies, how fatal those inconsistencies are, 
> I think we disagree.

FWIW, I'm not arguing that they are fatal. For instance, I don't think 
anybody has died out of his -- although I wouldn't want to tempt the 
devils in this respect, either :-) (local saying, so to speak)

IPv6 is mostly all about addressing. I believe we should be able to have 
clear definitions for these things. Or otherwise, just get rid of 
conflicting definitions.

> I believe adding a single word to the definition in 
> RFC4007 will align RFC4007 and RFC4193,  "uniquely identifying 
> interfaces anywhere *reachable* on the Internet".

This is tricky for two reasons:

1) Reachability depends on a lot of things, including filtering/security 
policies

2) this seems like a circular definition
e.g., link-local addresses are only reachable on the local link, because 
they have a link-local scope.  But, base on your definition, they are 
"link-local scope" because they are reachable only within the local link.

3) With your definition, link-locals could be considered GUAs: they are 
indeed unique anywhere reachable on the Internet (which for LLs happens 
to be"the local link").

> Further, I think when we eventually get around to revising RFC4291, 
> every remaining use of the word "scope" needs to be examined, and 
> probably a reference to the updated definition in RFC4007 or its 
> replacement should be added. Note most of the words "scope" in RFC4291 
> are in reference to local and global IIDs, which basically go away with 
> RFC7136. But even after that cleanup, I think there is some confusion 
> around "scope" and its meaning, at least for the uninitiated reader of 
> RFC4291.

It actually seems to be RFC4007 vs everything else. e.g., RFC4007 is at 
odds with RFC4193, too.

Thanks,

---

From: Fernando Gont <[email-masked]>
Date: Thu, 18 Feb 2021 20:58:24 -0300

> You can also argue, if there are prefix bits sent in the clear, and those prefix bits are used to send the packets to a pre-determined gateway, and that gateway is then used to decrypt all of the r…

"global span" is defined as "Internet-wide" span. i.e., if an address 
does not unambiguously specify an interface Internet-wide, it's not 
global scope as per RFC4007.

> Just sayin'. These still aren't like RFC 1918.

The only practical differences I see with respect to rfc1918 are:

1) ULAs are not intended to be used with NAT.
However, were RFC1918 strictly specified to be employed along with NAT? 
Besides "not indended" != "won't be".

2) ULAs are intended to have a small probability of collision when a 
subset of ULA-based networks are interconnected.

This is the product of mandating that some bits are generated from a 
PRNG, plus the fact that ULAs have more bits than their RFC1918 counterpart.

If I have missed any other differences, please enlighten me. :-)

Thanks,

---

From: Brian E Carpenter <[email-masked]>
Date: Fri, 19 Feb 2021 13:36:28 +1300

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.

All addresses have a region of reachability. This may be confined to a single "link" (whatever a "link" means), some type of limited domain (such as, but not limited to, a "site" (whatever a "site" means)), or to a large part of the Internet as a whole (knowing that there is in reality no such thing as "the" Internet.)

LL addresses MUST NOT be used off a given L2 link.
ULAs MUST NOT be routed outside a given limited domain.
GUAs MAY be routed anywhere.

(MANETs and other mesh networks don't fit in there very well.)

Regards
   Brian

---

From: Fernando Gont <[email-masked]>
Date: Thu, 18 Feb 2021 21:58:29 -0300

> 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.

FWIW, wfm. :-)

And, if one gets rid of "scopes", probably RFC4007 boils down to a much 
shorter document.

(Modulo: the multicast folks do use "scope" in a more "successful" way, 
IIRC?)

> (MANETs and other mesh networks don't fit in there very well.)

I guess limited-domain might also work for manets?

Thanks,

---

From: Mark Smith <[email-masked]>
Date: Fri, 19 Feb 2021 12:21:57 +1100

On Fri, 19 Feb 2021, 11:37 Brian E Carpenter, <[email-masked]>
wrote:

> 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?

ULAs (and addresses in general) have at least two different scopes:

- scope or domain of intended uniqueness

- scope or domain of intended forwarding within a network or across a set
of networks

There's others, for example, portions of the GUA space will have RIR
assignment scopes or IETF/IANA assignment scope.

"Scope" and "domain" seem to almost be synonyms. "Global domain", without
specifying what "domain" refers to, would have the same problems as the
term "global scope".

Regards,
Mark.

> All addresses have a region of reachability. This may be confined to a
> single "link" (whatever a "link" means), some type of limited domain (such
> as, but not limited to, a "site" (whatever a "site" means)), or to a large
> part of the Internet as a whole (knowing that there is in reality no such
> thing as "the" Internet.)
>
> >> You can also argue, if there are prefix bits sent in the clear, and
> those prefix bits are used to send the packets to a pre-determined gateway,
> and that gateway is then used to decrypt all of the remaining address bits,
> then route packets through a walled garden intranet with global span, then
> global scope could still apply.
> >

---

From: "Manfredi (US), Albert E" <[email-masked]>
Date: Fri, 19 Feb 2021 02:45:42 +0000

From: Mark Smith <[email-masked]> 

> "Scope" and "domain" seem to almost be synonyms. "Global domain", without specifying what "domain" refers to, would have the same problems as the term "global scope".

Yeah +1. Whether you say "scope," or whether your say "region of reachability," or even "domain," you're going to get exactly the same finicky complaints. IMO, we're best off just living with it. I honestly don’t believe the "inconsistencies" are crucial.

As to MANETs, they're in a class of their own. As if invented by people who had no clue what IP addresses are, and assumed they are just unique identifiers. Like a Social Security number, or a MAC address. You end up needing an exhaustive list of addresses reachable, or just default all along through a given gateway.

Bert

---

From: Fernando Gont <[email-masked]>
Date: Fri, 19 Feb 2021 00:06:42 -0300

On 18/2/21 22:21, Mark Smith wrote:
> 
> 
> On Fri, 19 Feb 2021, 11:37 Brian E Carpenter, 
> <[email-masked] <mailto:[email-masked]>> 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.
> 
> 

As per RFC4007, scope refers to address uniqueness.

> - scope or domain of intended uniqueness

For ULAs, this is "set of interconnected ULA-based networks" -- i.e., 
some sort of limited domain/scope.

> - 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: and address uniqueness will limit 
reachability.

> "Scope" and "domain" seem to almost be synonyms. "Global domain", 
> without specifying what "domain" refers to, would have the same problems 
> as the term "global scope".

Per RFC4007, it's global uniqueness it refers to.

That's why https://www.rfc-editor.org/rfc/rfc8190.txt introduced the 
flag "globally reachable" to the "IANA IPv6 Special-Purpose Address 
Registry".

Thanks,

---

From: Fernando Gont <[email-masked]>
Date: Fri, 19 Feb 2021 00:14:06 -0300

> Yeah +1. Whether you say "scope," or whether your say "region of reachability," or even "domain," you're going to get exactly the same finicky complaints. IMO, we're best off just living with it. I…

I don't believe they are crucial.

But eventually this needs to be explained (whether in courses, books) or 
understood by people that just want to read and understand the specs.

Given IPv6 is mostly all about addressing, and that have a "scoped 
addressing architecture", it'd be nice to be able to agree on what scope 
actually means -- in a way that such definition works across specs -- or 
simply get rid of this and any other problematic terms.

Thanks,

---

From: Gert Doering <[email-masked]>
Date: Sat, 20 Feb 2021 15:09:01 +0100

Hi,

> > 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.

Seconded.

> (Modulo: the multicast folks do use "scope" in a more "successful" way, 

Their definitions are at least somewhat more clear on what a "scope" is -
send a packet to that address, and this is how far it will get.

In practice, how much IPv6 multicast is there which is not "node" and
"link" scoped?  Or, to be even more picky, not "link" scoped?

Gert Doering
        -- NetMaster
-- 
have you enabled IPv6 on something today...?

SpaceNet AG                      Vorstand: Sebastian v. Bomhard, Michael Emmer
Joseph-Dollinger-Bogen 14        Aufsichtsratsvors.: A. Grundner-Culemann
D-80807 Muenchen                 HRB: 136055 (AG Muenchen)
Tel: +49 (0)89/32356-444         USt-IdNr.: DE813185279

---

From: Vasilenko Eduard <[email-masked]>
Date: Sat, 20 Feb 2021 14:17:13 +0000

Indeed,
If something could be implemented through all continents in one case
But may have the significance "one link only" in another case,
Then any "Scope" classification for this thing would be misleading.
Better explanation is here: https://en.wikipedia.org/wiki/Occam%27s_razor
Ed/
-----Original Message-----
From: ipv6 [mailto:[email-masked]] On Behalf Of Gert Doering
Sent: Saturday, February 20, 2021 5:09 PM
To: Fernando Gont <[email-masked]>
Cc: IPv6 Operations <[email-masked]>; [email-masked]
Subject: Re: [v6ops] Scope of Unique Local IPv6 Unicast Addresses (Fwd: New Version Notification for draft-gont-6man-ipv6-ula-scope-00.txt)

Hi,

Seconded.

> (Modulo: the multicast folks do use "scope" in a more "successful" 

Their definitions are at least somewhat more clear on what a "scope" is - send a packet to that address, and this is how far it will get.

In practice, how much IPv6 multicast is there which is not "node" and "link" scoped?  Or, to be even more picky, not "link" scoped?

Gert Doering
        -- NetMaster

---

From: Ted Lemon <[email-masked]>
Date: Sat, 20 Feb 2021 09:42:54 -0500

> "link" scoped?  Or, to be even more picky, not "link" scoped?

It’s being used in the context of IoT to do mass events, like turning on all the lights in a context where the switch is on link A, and some lights are on links B and C, for example. The motivation for doing this is that in principle multicast uses less of the constrained bandwidth of the IoT network. This can work because even when this sort of partition happens, there is a common infrastructure backbone that can handle the multicast routing issues. The old dream of multicast video on the internet seems to be dead, but that doesn’t mean that off-link multicast is never useful.

---

From: Fernando Gont <[email-masked]>
Date: Sat, 20 Feb 2021 11:46:31 -0300

>>> 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.

That said, just ran into this I-D, that also makes use of "scope": 
draft-king-irtf-challenges-in-routing

> "link" scoped?  Or, to be even more picky, not "link" scoped?

I guess that depends a lot on the deployment environment. For the 
general case, the answer is "hardly any". But then I'm told that in e.g. 
some stock markets they are *required* to emply multicast to spread some 
information.

Thanks,

---

From: Mark Smith <[email-masked]>
Date: Sun, 21 Feb 2021 08:54:58 +1100

> 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.

> 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)."

> Normally, both of these are equal:

In ULAs they aren't.

Link-Local addresses generated using RFC7271s aren't either.

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
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.

and address uniqueness will limit
> reachability.

I'm not sure I understand what you're saying.

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.

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).

Regards,
Mark.

---

From: Mark Smith <[email-masked]>
Date: Sun, 21 Feb 2021 09:03:39 +1100

> some stock markets they are *required* to emply multicast to spread some

Australian Stock Exchange was using multicast to brokers in the
mid-1990s. I don't know if it is now, however that's just because I
haven't had any contact with anybody who has done anything in that
environment since.

I thought it was for distributing share prices, however I've also come
across "hoot-n-holler" networks, so it might have been voice:

https://en.wikipedia.org/wiki/Hoot-n-holler

> _______________________________________________
> v6ops mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/v6ops

---

From: Fernando Gont <[email-masked]>
Date: Sun, 21 Feb 2021 04:18:53 -0300

Hi, Mark,

> 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.

>        - 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"

>> Normally, both of these are equal:

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.

> 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.

> 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.

> 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)

> of the network, because the main use of the term I've encountered is

Reachability: topological span where a packet with said address could 
possibly be forwarded to.

> duplicate addresses (i.e. anycast).

The above would apply.

Thanks,

---

From: Mark Smith <[email-masked]>
Date: Tue, 23 Feb 2021 09:49:42 +1100

> all developments -- unless updated.

Did you miss this?

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

---

From: Owen DeLong <[email-masked]>
Date: Tue, 23 Feb 2021 15:18:44 -0800

> On Feb 20, 2021, at 6:09 AM, Gert Doering <[email-masked]> wrote:
> 
> Hi,
> 

Well, yes and no… Most of the scopes that are defined have extraordinarily variable
meaning:
	Admin-Local
	Site-Local
	Organization-Local

However, yes, Interface, Link, and Global are well defined even though it is common for
people to fail to grasp the difference between interface-local and link-local.

I will, however, argue that link-local scope is well defined as a scope for IPv6 addresses in fe80::/10.

> "link" scoped?  Or, to be even more picky, not "link" scoped?

A lot less than there should be.

Owen

---

From: Owen DeLong <[email-masked]>
Date: Tue, 23 Feb 2021 16:11:42 -0800

>      - Globally unique prefix (with high probability of uniqueness)."

Or in other words, “Globally maybe unique prefix, probably, we hope,
_IF_ everyone follows the directions.”

>> Normally, both of these are equal:

Well, we don’t really know that… The scope of a collection of cooperating
networks choosing to exchange ULA routes could become global. It’s not
likely to, but it’s not impossible, either.

> link, however the RFC7217 LL address's scope of uniqueness is global.

Again, you’re talking about its scope of likely uniqueness and said
uniqueness is for all practical purposes nearly accidental and certainly
not a criteria of validity.

The scope of guaranteed uniqueness is link.

> I'm not sure I understand what you're saying.

Well… Two hosts with the same address on different networks are pretty
unlikely to be able to communicate. Thus, reachability is impaired.

> of the network, because the main use of the term I've encountered is

I think in this context it refers to the ability to get a packet from
arbitrary host A to arbitrary host B. If A and B have unique addresses,
then this may be possible. If A and B have identical addresses, then this
is unlikely (absent stupid NAT tricks).

> duplicate addresses (i.e. anycast).

The forwarding domain is what is intended to be possible within the established
limits. However, lack of uniqueness in addressing certainly constitutes one
of the limits imposed on the possible forwarding domain.

Owen

---

From: Gert Doering <[email-masked]>
Date: Thu, 25 Feb 2021 17:59:15 +0100

Hi,

> A lot less than there should be.

I beg to differ on that...  among all the problems IPv6 has, "lack of
multicast" is not one...

Wide-scale routed multicast is a very nice idea, but totally non-deployable
across network boundaries in reality.  We've tried, for many years (with
IPv4), and every time a customer wanted to use it, it was broken in some
non-debuggable way (like, RP-Tree selecting a path in 3549 where they forgot
to turn on PIM on the interfaces...).

Even on-link multicast gets broken by switch vendors often enough.

Gert Doering
        -- NetMaster