Subject: RE: Open issues list? [Re: New (-02) version of IPv6 CPE Router draft is available for review]

From: Francois-Xavier Le Bail <[email-masked]>
Date: Thu, 31 Jul 2008 00:39:55 -0700 (PDT)

--- On Wed, 7/30/08, Hemant Singh (shemant) <[email-masked]> wrote:
> However, the Loopback interface has other uses. Please see
> the slide titled "Routing Domains and Address assignments"
> from our v6ops presentation and see that the Loopback interface
> in the picture is being used with an anycast address for ICMP health
> check (as per RFC4241).

The RFC4241 in his section 2.8. Connectivity Monitoring say:
"The old document of APNIC IPv6 address assignment policy required
that APNIC could ping the subnet anycast address to check address usage."

But the APNIC ipv6-policy-280599 is obsolete and the actual policy
(http://www.apnic.net/policy/ipv6-address-policy.html) dont have such
"check address usage".

So, the RFC4241 cannot be used as argument in favour of a loopback interface.

Francois-Xavier

---

From: "Hemant Singh (shemant)" <[email-masked]>
Date: Thu, 31 Jul 2008 03:44:38 -0400

During the presentation at IETF, it was clearly said, the picture is one
addressing scheme.  One may use some other addressing scheme as well.
However, the bullets in that slide do reflect current CPE Router
addressing plan.

Forget RFC4241 for a moment - any router has a loopback interface.  What
one configures on the Loopback interface is left to the user.

Hemant 

-----Original Message-----
From: Francois-Xavier Le Bail [mailto:[email-masked]] 
Sent: Thursday, July 31, 2008 8:40 AM
To: Hemant Singh (shemant)
Cc: Iljitsch van Beijnum; [email-masked]
Subject: RE: Open issues list? [Re: New (-02) version of IPv6 CPE Router
draft is available for review]

--- On Wed, 7/30/08, Hemant Singh (shemant) <[email-masked]> wrote:
> However, the Loopback interface has other uses. Please see the slide 
> titled "Routing Domains and Address assignments"
> from our v6ops presentation and see that the Loopback interface in the

> picture is being used with an anycast address for ICMP health check 
> (as per RFC4241).

The RFC4241 in his section 2.8. Connectivity Monitoring say:
"The old document of APNIC IPv6 address assignment policy required that
APNIC could ping the subnet anycast address to check address usage."

So, the RFC4241 cannot be used as argument in favour of a loopback
interface.

Francois-Xavier

---

From: Francois-Xavier Le Bail <[email-masked]>
Date: Thu, 31 Jul 2008 01:10:27 -0700 (PDT)

--- On Thu, 7/31/08, Hemant Singh (shemant) <[email-masked]> wrote:
> any router has a loopback.

It is not true.

In a previous e-mail, you wrote:
"I agree with you that Loopback interfaces are not common to home
Linksys-like routers."

Francois-Xavier

---

From: "Hemant Singh (shemant)" <[email-masked]>
Date: Thu, 31 Jul 2008 04:15:54 -0400

It's because Linksys does not configure it or expose the Loopback
interface to the user! Any router has a Loopback interface! 

Hemant 

-----Original Message-----
From: Francois-Xavier Le Bail [mailto:[email-masked]] 
Sent: Thursday, July 31, 2008 9:10 AM
To: Hemant Singh (shemant)
Cc: Iljitsch van Beijnum; [email-masked]
Subject: RE: Open issues list? [Re: New (-02) version of IPv6 CPE Router

It is not true.

Francois-Xavier

---

From: Antonio Querubin <[email-masked]>
Date: Wed, 30 Jul 2008 22:55:57 -1000 (HST)

> interface to the user! Any router has a Loopback interface!

Can we please not go down this rabbit hole again?  It's the observable 
behaviour that matters.

Antonio Querubin
whois:  AQ7-ARIN

---

From: Gert Doering <[email-masked]>
Date: Thu, 31 Jul 2008 15:15:52 +0200

Hi,

> interface to the user! Any router has a Loopback interface! 

"could have"

If not configured, all my Cisco routers do *not* have Loopback interfaces.

Gert Doering
        -- NetMaster
-- 
Total number of prefixes smaller than registry allocations:  128645

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

---

From: Pekka Savola <[email-masked]>
Date: Thu, 31 Jul 2008 16:26:12 +0300 (EEST)

> If not configured, all my Cisco routers do *not* have Loopback interfaces.

If you ping 127.0.0.1, does the router respond? 
Which interface has that address?

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

---

From: Gert Doering <[email-masked]>
Date: Thu, 31 Jul 2008 15:30:37 +0200

Hi,

> If you ping 127.0.0.1, does the router respond? 

No.

> Which interface has that address?

None.

Cisco>ping 127.0.0.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 127.0.0.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
Cisco>sh ip route 127.0.0.1
% Network not in table

(I know that some Cisco boxes use 127.0.0.x for internal communication
between blades in a multi-CPU-chassis, like the catalyst 5xxx/6xxx 
switches - but that's very much *not* a loopback thing)

Gert Doering
        -- NetMaster

---

From: "Hemant Singh (shemant)" <[email-masked]>
Date: Thu, 31 Jul 2008 09:43:38 -0400

Agreed, Gert.

Hemant 

-----Original Message-----
From: Gert Doering [mailto:[email-masked]] 
Sent: Thursday, July 31, 2008 2:16 PM
To: Hemant Singh (shemant)
Cc: Francois-Xavier Le Bail; Iljitsch van Beijnum; [email-masked]
Subject: Re: Open issues list? [Re: New (-02) version of IPv6 CPE Router

Hi,

"could have"

If not configured, all my Cisco routers do *not* have Loopback
interfaces.

Gert Doering
        -- NetMaster

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

---

From: "Stark, Barbara" <[email-masked]>
Date: Thu, 31 Jul 2008 13:36:01 -0400

>It's the observable behaviour that matters.
>
> Antonio Querubin

I really agree with this statement, and wonder if it would be more
useful to describe externally observable behavior, than to try to
specify implementation (loopback interfaces and such). And identify what
external stimuli the CPE router needs to be able to respond to, and what
those responses are. I look at CPE routers as black boxes. Either they
behave the way I want, or they don't. What they do on the inside to
behave that way, doesn't really matter to me. I can't test that -- I can
only test what I can observe.

That is, when a CPE router's WAN interface is connected to the access
network, the access network sees messages coming from the CPE router,
and sends messages in return (router advertisements and such).

Given that we appear to agree that the access network dictates whether
stateful or stateless address assignment happens, and whether or not it
hands out a global address (i.e., whether or not the access network uses
the numbered or unnumbered model), the CPE router that expects to work
on all types of access networks needs to be prepared to respond
appropriately to all of these cases. A CPE router that is specifically
designed to only operate on a particular network doesn't need to be
prepared for all of these cases, but I'm not really interested in
specifying that CPE router in the IETF. As I've stated before, my
biggest concern are the retail CPE routers with Ethernet WAN ports.

The non-network-specific CPE router must be prepared to act
appropriately when it gets a GUA (through SLAAC or stateful DHCPv6). It
must also be prepared to act appropriately (from the perspective of an
external observer) when it does not. In my opinion, a
non-network-specific CPE router must also boot with LAN coming up
without dependency on the WAN (the LAN before WAN boot mode). 

If the "loopback interface" somehow appears different to the access
network, and the access network needs to know this, then this interface
is relevant. If the access network (or the LAN, either) cannot tell that
there is a loopback interface, or doesn't care, then such an
implementation isn't relevant.

What I do care about is the GUA that the CPE router uses when it
initiates IP traffic to other global addresses (not within its assigned
prefix). I think it should use an address from the prefix. If the access
network didn't give it a GUA (unnumbered model), then I think it *must*
use an address from the prefix. I don't really care how this is
implemented internally, so long as there is agreement that it is
possible and acceptable that this be able to occur. I don't care if this
address is somehow connected to the "WAN interface", or not. So long as
the router uses it.

Barbara