RE: New (-02) version of IPv6 CPE Router draft is available for review

["Hemant Singh (shemant)" <shemant@cisco.com>]

David,

Barring Shin's concern that even if a LAN interface on the CPE Router is
up with a GUA but the WAN interface of the CPE Router does not have a
GUA acquired, using a GUA of a LAN interface is fine as source for WAN
packet to the SP.  This is the Cisco IOS unnumbered interface model.
Then the Loopback interface is not required.  Sorry, some folks like
Iljitsch thought our draft was alluding to the Cisco IOS unnumbered
interface model seeing the "Unnumbered Model" section of our draft.  Our
draft was NOT referring to the IOS unnumbered model, we just used the
term in our draft to signify that the WAN doesn't have a GUA assigned to
it.  The Unnumbered Model is our -02 draft was merely providing a
solution with Loopback interface that folks had asked for at the time.

Sorry, I haven't been able to understand all of Shin's concerns
completely and that is why I am meeting him at IETF to get to the bottom
of things.  As a separate observation, Ole has shot down the Shin
1plusus64s draft and the draft's concern in section 4.  I don't
understand all of Shin's concerns to shoot down his draft or not. 

Yes, the internals of the CPE Router does include a bridge that is
always up if the router is powered up.  Further, notice from RFC4241
that the Loopback interface used in that RFC's DSL Deployment is
provisioned for an anycast address for ping checks.  We will add such
information to our draft that the optional Loopback interface can be
spawned for the anycast address ping.  

Hemant & Wes

-----Original Message-----
From: David Miles [mailto:davidm@thetiger.com] 
Sent: Thursday, July 24, 2008 3:44 AM
To: Hemant Singh (shemant)
Cc: v6ops WG
Subject: Re: New (-02) version of IPv6 CPE Router draft is available for
review

>
> Some comments on draft-02:
> - The un-numbered  model doesn't require a loopback interface
>
> <hs>
> It does.  You may be behind checking your emails on this thread.   
> Please
> read ample evidence given for this one.
> </hs>
>


When Shin was pointing out the considerations for a loopback, Francois-
Xavier noted:
"When the CPE router has only a link-local address on the WAN port, if
the CPE has a LAN bridge, I hope there is an option to have the global-
scope address set on the LAN bridge (from IA_PD via DHCPv6) as an
alternative to loopback solution."
Between Shin, Francois-Xavier, Ole and others it seemed there was an
appreciation that loopbacks were not required to support the unnumbered
model - best summarised in Shin's email on 3 July. (I'm not suggesting
everyone thought the unnumbered model was preferred, but that there was
no technical obstacle).

RFC 3484 says:
It is RECOMMENDED that the candidate source addresses be the set of
unicast addresses assigned to the interface that will be used to send to
the destination. (The "outgoing" interface.) On routers, the candidate
set MAY include unicast addresses assigned to any interface that
forwards packets, subject to the restrictions described below.
This seems to hit the nail on the head - we are describing a router that
MAY use a unicast address assigned to any interface (LAN) subject to the
restrictions in RFC 3484 (which do not pose any problem in my
interpretation). I initially raised the use of a loopback as an option
because I was concerned about LAN interface state (and said so in the
original thread). If the LAN interface is a bridge (always up) I see no
mandatory need for a loopback. I would urge continued discussion in-
list if there are technical arguments against a un-numbered model
without loopback. The two points raised in favour of such an option are
that : it avoids an additional /64 for the loopback, and; caters to CPE
that may not support a loopback interface (may need to be qualified).

IE (a reference for a routing CPE with internal MAC bridge):

       +------------------------+
       | Routing CPE w/ bridge  |
       | +------+     +------+  |
Port1-|-|      |     |      |  |
       | |Bridge|-----|Router|--|----WAN
Port2-|-|      |  LAN|      |  |
       | +------+     +------+  |
       +------------------------+


LAN is connected to a bridge device so it is always up.

Addresses:
WAN: 	fe80::<iid>%wan prefixlen 64
LAN:  	2001:db8:0:1::<iid> prefixlen 64 (example)
		fe80::<iid>%lan prefixlen 64