Subject: review of draft-ietf-6man-multi-homed-host-07

From: Mikael Abrahamsson <[email-masked]>
Date: Fri, 19 Aug 2016 13:30:21 +0200 (CEST)

Reading it as if I never read it before.

1.1

I think the "multi-interface router (MIF)" acronym here warrants a bit 
more introduction. The word "MIF" first occurs in the diagram, before it's 
ever been defined in the document.

"Hence, if the router is a multi-interface (MIF) router"

Routers typically have multiple interfaces....?

Speaking of which, "two interfaces sharing a prefix". What does that 
mean? That they're for instance /64s from the same /56? If it's the same 
/64, then it seems this router isn't a router, it's a switch?

I then read the rest, and nothing else came up. My only thought here was 
that the document is very light on prescriptive language. It says what to 
do, but without saying exactly how. Is this on purpose, that we want to 
leave that up to the implementor? Do we foresee a v6ops document outlining 
more operational recommendations for implementors?

Apart from that, I am 100% behind the ideo of this document and it's my 
firm opinion that the kind of behaviour described in it is crucial that 
clients implement in order to enable interoperation with complex networks 
going forward.

What would be interesting to discuss is what to do with other information, 
what resolver should a client use? If it has two interfaces with two 
different prefixes and two different resolvers, should source address 
selection somehow influence (or be influenced by) what DNS resolver 
currently in use? What about other services? NTP? SMTP? I imagine we don't 
want that in this document, but I would imagine it's something that has to 
be fixed somewhere?

-- 
Mikael Abrahamsson    email: [email-masked]

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From: Suresh Krishnan <[email-masked]>
Date: Fri, 19 Aug 2016 12:41:41 +0000

Hi Mikael,
   Thanks for your review. This document has already been evaluated by the 
IESG and is close to being approved after the next version will be posted. 
The IESG evaluation is here

https://datatracker.ietf.org/doc/draft-ietf-6man-multi-homed-host/ballot/

Adding new prescriptive language to this draft at this point is not going to 
be appropriate. If you feel strongly that there are blocking concerns with 
the current draft, please contact the chairs, authors and me offline to 
discuss the possibilities.

Regards
Suresh

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From: Brian E Carpenter <[email-masked]>
Date: Sat, 20 Aug 2016 08:27:23 +1200

> discuss the possibilities.

There is going to be another spin of the document to address concerns that came
up at the very end of IETF Last Call and during IESG review - just waiting
for the last word from the IESG discussion. But my own opinion is that to
add more normative language is very difficult, because the details are mixed
up with implementation choices. What we have done, as you'll see when the
next version appears, is to be more precise about which bits of RFC 4861 are
extended.

Beyond that, see
https://mailarchive.ietf.org/arch/msg/v6ops/6r_FOp8DGRZ0PjhmhCiXoi_AM2Y

   Brian

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From: Mikael Abrahamsson <[email-masked]>
Date: Sat, 20 Aug 2016 05:51:37 +0200 (CEST)

> https://mailarchive.ietf.org/arch/msg/v6ops/6r_FOp8DGRZ0PjhmhCiXoi_AM2Y

Ok, I understand. I think the document is fine without prescriptive 
language, the result is just that I think we'll end up with a future v6ops 
document giving guidance on these topics. I think that's fine as well.

But my other comment regarding MIF and the shared prefix still stands, if 
there is a document respin could you please take a look at my comment and 
see if minor edit can be made to clarify that for the reader?

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From: Brian E Carpenter <[email-masked]>
Date: Sat, 20 Aug 2016 16:10:11 +1200

> see if minor edit can be made to clarify that for the reader?

Yep. I changed the caption in the figure. I didn't change the text
about "MIF" because I couldn't really see putting "multiple, i.e. more
than two" and I think the figure makes it fairly clear.

(If English had a word for "more than two" that would be great. Actually,
some dictionaries claim that "several" means "more than two" but I think
that is a very academic definition and not helpful for the international
readership of RFCs.)

Rgds
    Brian

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From: Mikael Abrahamsson <[email-masked]>
Date: Sat, 20 Aug 2016 06:37:59 +0200 (CEST)

> that is a very academic definition and not helpful for the international

Ok, that was my lesser concern. The "sharing a prefix" is much bigger.

               +-----------------+
               |                 |
               |     MIF Router  +---/--- other interfaces
               |                 |
               +---+---------+---+
                   |         | Two interfaces sharing a prefix
                 --+-+--   --+-+--
                     |         |
                  +--+---------+--+
                  |   MIF Host    |
                  +---------------+

                 Figure 1: Hypothetical MIF interconnection

"Two interfaces sharing a prefix"

I spent 5-10 minutes pondering 1.1 and I still can't figure it out. I see 
a router, it has two interfaces. I have to take for granted that this 
router has routed ports, and typically routers don't allow for overlapping 
address space, so these two ports would have different /64s? Or are they? 
So what's the prefix shared? Upstream /56? Now I'm just guessing.

So I just can't figure it out. Or is this a router with a built in switch 
and it's the same /64 on both ports? I just think there is clarification 
needed in 1.1, and if there is a re-spin, I think the document would be 
better if that could happen.

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From: [email-masked]
Date: Mon, 22 Aug 2016 12:24:04 +0200

> I spent 5-10 minutes pondering 1.1 and I still can't figure it out. I see a router, it has two interfaces. I have to take for granted that this router has routed ports, and typically routers don't allow for overlapping address space, so these two ports would have different /64s? Or are they? So what's the prefix shared? Upstream /56? Now I'm just guessing.
> 
> So I just can't figure it out. Or is this a router with a built in switch and it's the same /64 on both ports? I just think there is clarification needed in 1.1, and if there is a re-spin, I think the document would be better if that could happen.

Re-reading this I also share your confusion.

While the section explors the weak/strong host models and tries to exemplify the problem, I think the example might be a little confusing as Mikael points out.

"Two interfaces sharing a prefix"; (assuming we're talking onlink prefixes here) can only happen for fe80::/10 right?

"For example, a host with a link-local-only interface and a default route pointing to that interface"

What if this text is removed:

   Hence, if the router is a multi-interface (MIF) router and is using the same prefix on two or more
   LANs shared by the host (as in Figure 1), the host might use each of
   those LANs and meet the requirement.

And s/Two interfaces sharing a prefix/Link-local only prefix/ in the caption.

Cheers,
Ole

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From: Brian E Carpenter <[email-masked]>
Date: Tue, 23 Aug 2016 13:05:19 +1200

> "Two interfaces sharing a prefix"; (assuming we're talking onlink prefixes here) can only happen for fe80::/10 right?

Yes, and I don't think that's what Fred intended when he wrote
this. I *think* he meant that the two interfaces both have prefixes
(of length L) taken out of the same shorter prefix (e.g. of length L-16).
Or to give a very specific example, the two subnets have prefixes
2001:db8:aaaa:1::/64 and 2001:db8:aaaa:2::/64 and the site
has a WAN prefix 2001:db8:aaaa::/48 .

Does that seem right? If so, I certainly need to fix the text some more.

    Brian

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From: [email-masked]
Date: Tue, 23 Aug 2016 10:45:37 +0200

Brian,

> Does that seem right? If so, I certainly need to fix the text some more.

'Two interfaces with subnets from the same prefix' ?

cheers,
Ole

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From: Hemant Singh <[email-masked]>
Date: Tue, 23 Aug 2016 07:27:27 -0400

Right, which router will let one configure two interfaces with the same
subnet for IP address configuration.  This is why others have already
suggested that the two interfaces are using a link-local address.

Hemant

On Tue, Aug 23, 2016 at 4:45 AM, <[email-masked]> wrote:

> >>> I spent 5-10 minutes pondering 1.1 and I still can't figure it out. I
> see a router, it has two interfaces. I have to take for granted that this
> >>> So I just can't figure it out. Or is this a router with a built in
> switch and it's the same /64 on both ports? I just think there is
> clarification needed in 1.1, and if there is a re-spin, I think the
> document would be better if that could happen.
> >>
> >> While the section explors the weak/strong host models and tries to
> exemplify the problem, I think the example might be a little confusing as
> Mikael points out.
> >>
> >> "Two interfaces sharing a prefix"; (assuming we're talking onlink
> prefixes here) can only happen for fe80::/10 right?
> >