Subject: [Int-dir] INT area directorate review for draft-ietf-6man-multi-homed-host-06

From: Zhen Cao <[email-masked]>
Date: Tue, 7 Jun 2016 22:33:11 +0800

Hi,

I am an assigned INT directorate reviewer for draft-ietf-6man-multi-
homed-host-06.txt. These comments were written
primarily for the benefit of the Internet Area Directors. Document
editors and shepherd(s) should treat these comments just like they
would treat comments from any other IETF contributors and resolve them
along with any other Last Call comments that have been received. For
more details on the INT Directorate, see http://www.ietf.org/iesg/direc
torate.html.

Thank authors for this work.

Overall, this is a well-written draft. It clearly specifies what a
multi-homed host needs to take into account while making default route
and source address selections, especially when a certain in-path
filter/middleboxes may prevent successful communication.

One cent for discussion as below:

>3.2.  Default Router Selection
>
>Default Router Selection is modified as follows: A host SHOULD select
>default routers for each prefix it is assigned an address in.
>Routers that have advertised the prefix in its Router Advertisement
>message SHOULD be preferred over routers that do not advertise the
>prefix.

If both routers have not advertised the prefix, how will the host make
the decision?

A normal daily example is a host being connected to the Internet via
one router, and at the same time connected to a VPN to a private
domain which is further connected to global Internet.  If the host
initiates communication with some public internet address(not
advertised by either link), it is sometimes undefined which route to
take because both links connect to that destination.  From my
understanding, route metric will be take into account in this case.  I
do experience different VPN clients behave differently because their
assignment of the VPN link metric.  A note to this case might be
useful for readers.

Many thanks,
Zhen

---

From: Zhen Cao <[email-masked]>
Date: Tue, 7 Jun 2016 22:42:20 +0800

Excuse me for resending due to the use of a wrong author email alias.

I believe it is in a good shape for publication.

Many thanks,
Zhen

---

From: Brian E Carpenter <[email-masked]>
Date: Wed, 8 Jun 2016 08:11:04 +1200

Hi Zhen,

Thanks for the review.

> If both routers have not advertised the prefix, how will the host make

You mean, no router advertised it? We could simply state that this case
is out of scope for the document, but I guess it would be clearer to
state that normal routing metrics will apply.

> assignment of the VPN link metric.  A note to this case might be

I've had no experience of that with IPv6. I did have it for IPv4 with a
previous employer, and the VPN came with a very complex set of host routes
that answered this question.

    Brian

---

From: Zhen Cao <[email-masked]>
Date: Wed, 8 Jun 2016 09:52:25 +0800

On Wed, Jun 8, 2016 at 4:11 AM, Brian E Carpenter <
[email-masked]> wrote:

> You mean, no router advertised it?

> We could simply state that this case

Good to me.

> that answered this question.

Exactly true.

Cheers,
Zhen