Subject: [homenet] hierarchial assignment in draft-chakrabarti-homenet-prefix-alloc

From: Michael Richardson <[email-masked]>
Date: Tue, 01 Nov 2011 10:51:54 -0400

I read draft-chakrabarti-homenet-prefix-alloc as being the simplest
thing that might work.  We discussed this hierarchy at the interim
meeting, and we were not generally happy with it, as it seemed we were
restricting IPv6 to fail whenever IPv4 would fail, when we felt we could
in fact do better.  

We further felt that the incidence of users plugging in the wrong port
(plugging the "LAN" into the uplink on the CER), was sufficiently common
that it would be nice to have a system that was immune to this.

The analysis that 3 bits of a /56 gives us essentially three levels of
delegation, and that's probably enough for most places.  

The discussion in section 12 is a bit satisfying that actually IPv6 can
operate better than IPv4.  Figure 6 is likely quite common, particularly
when one considers that Network C is wireless and Network C/D (router Y)
is in fact wired, and the culprit is a PC in bridging mode.  This
happens ridiculously often.  The worst affects in figure 6 in IPv4 are
due to IP address clashes.  If equipment X and Y are from different
vendors, then the IPv4 address clash often goes away, and I've heard lots
of anecdotal stories from less technical friends about how you can never
have more than one router from the same vendor.

That pathology described in figure 7, is, I think, less frequent, simply
because having that many layers is uncommon.  I want to point out that
if router 4 does in fact pict router 3 as it's uplink, router 4 will be
the fourth level, and it will just barely get one /64, in the /56
divided by 3 bits...  The heuristic suggested at the end may be well
worthwhile, as it would make R4 prefer R1.

Some detailed comments:

From draft-chakrabarti-homenet-prefix-alloc:

>3.  Conceptual model of a Basic Home Router
>
>   A key assumption we make is that a Basic Home Router has a designated
>   uplink port.  Today such home routers include IPv4 NAT functionality
>   and as IPv6 support is added the goal is to not require IPv6 NAT
>   functionality but instead rely on different prefixes being allocated
>   to different links.

Can we change this text to say:

    A key assumption we make is that a Basic Home Router the ability to
    designate a port as the uplink port.  This may be by external
    convention (a label), or via a to-be-determined heuristic.
    Today such home routers include IPv4 NAT functionality...

(and  s/port is colors/port is colored/)

section 11:
>   The only exception to this is a CER which has been
>   configured to generate and advertise a ULA prefix even when the ISP
>   connection is down; such a CER would sub-delegate and advertise the
>   ULA prefix in parallel with requesting a prefix delegation from the
>   ISP.

What I understand is that a CER which is in factory default
configuration (therefore has never generated a ULA before), which never
connects to an ISP, will not generate a ULA without a manual configuration.
Configuration of the CER would have to be done by link-local address.

I had to write the above sentence out to convince myself that this was an
acceptable compromise.

Why would a CER which has generated a ULA care of it's never connected
to an ISP again?