Subject: Re: I-D Action:draft-ietf-v6ops-ipv6-cpe-router-02.txt

From: Hiroki Sato <[email-masked]>
Date: Tue, 03 Nov 2009 00:51:03 +0900 (JST)

Hi,

[email-masked] wrote
  in <[email-masked]>:

In> A New Internet-Draft is available from the on-line Internet-Drafts directories.
In> This draft is a work item of the IPv6 Operations Working Group of the IETF.
In>
In>
In> 	Title           : Requirements for IPv6 Customer Edge Routers
In> 	Author(s)       : H. Singh, et al.
In> 	Filename        : draft-ietf-v6ops-ipv6-cpe-router-02.txt
In> 	Pages           : 14
In> 	Date            : 2009-10-26

(Section 4.1)
 | When the router is attached to the WAN interface link it must act as
 | an IPv6 host for the purposes of IPv6 interface initialisation, ND
 | Router Discovery, Prefix Discovery and interface address assignment
 | ([RFC4861]/[RFC4862]).  The router acts as a requesting router for
 | the purposes of DHCP prefix delegation ([RFC3633]).

 I think this description is unclear whether the router must "act as
 an IPv6 host" on WAN side even after interface initialization or not.
 More specifically, 1) we should set or not the R-bit in Neighbor
 Advertisement messages on WAN side, and 2) the WAN interface can
 respond to Router Solicitation messages or not.

 IMO when the CE router is working as an IPv6 router (IsRouter flag in
 RFC4861 is enabled) after the provisioning, the IPv6 router behavior
 of Neighbor Discovery makes sense.  If the IP forwarding is disabled
 for some reason, acting as a host on WAN interface link would be
 reasonable for re-initialization.

 Anyway, the description in Section 4.1 can be improved by making this
 point (when it must act as a host and when it must act as a router)
 clear.

-- Hiroki

---

From: Ole Troan <[email-masked]>
Date: Tue, 3 Nov 2009 10:23:10 +0100

Hiroki,

>  respond to Router Solicitation messages or not.

for the purposes of SLAAC, router discovery etc it should always act
as a host on the WAN interface. it should not reply to RS messages nor
set the R-bit in NAs.
I'll take a stab at better text, but feel free to suggest something.

>  reasonable for re-initialization.

IP forwarding is enabled on the WAN interface. it is only for address
assignment that the host functions of RFC4861/4862 are used. the
interface is acting as _both_ a router and a host on the interface.

>  point (when it must act as a host and when it must act as a router)

it acts as both. again, feel free to submit better text.

cheers,
Ole

---

From: Hiroki Sato <[email-masked]>
Date: Thu, 05 Nov 2009 02:17:29 +0900 (JST)

Ole Troan <[email-masked]> wrote
  in <[email-masked]>:

ot> Hiroki,
ot> 
ot> > (Section 4.1)
ot> >  | When the router is attached to the WAN interface link it must act as
ot> >  | an IPv6 host for the purposes of IPv6 interface initialisation, ND
ot> >  | Router Discovery, Prefix Discovery and interface address assignment
ot> >  | ([RFC4861]/[RFC4862]).  The router acts as a requesting router for
ot> >  | the purposes of DHCP prefix delegation ([RFC3633]).
ot> >
ot> >  I think this description is unclear whether the router must "act as
ot> >  an IPv6 host" on WAN side even after interface initialization or not.
ot> >  More specifically, 1) we should set or not the R-bit in Neighbor
ot> >  Advertisement messages on WAN side, and 2) the WAN interface can
ot> >  respond to Router Solicitation messages or not.
ot> 
ot> for the purposes of SLAAC, router discovery etc it should always act
ot> as a host on the WAN interface. it should not reply to RS messages nor
ot> set the R-bit in NAs.

 Thank you for the clarification.  Correct me if I am wrong, but in my
 understanding, for router discovery and SLAAC the node must
 accept/process RAs and must discard received RSes.  This means
 "acting as a host", but is there a technical reason to always set
 R-bit in NAs zero?  A CE router has a moment of transition from a
 host to a router (after provisioning, for example) and vice versa as
 viewed from the PE router, so making R-bit depend on whether IP
 forwarding is enabled or not still seems reasonable to me.

 Even if doing so the R-bit should not prevent the CE router from
 router discovery or SLAAC.  While pretending a host by always setting
 the R-bit zero would work certainly, to me there is no strong reason
 to disable the functionality.

 So, I think acting as a host with regard to RS/RA is needed on WAN
 interface, but NS/NA do not always need to do so.  Is this a wrong
 idea?  What I mean in writing is something like the following:

 | When the router is attached to the WAN interface link it must act as
 | an IPv6 host for the purposes of IPv6 interface initialisation, ND
 | Router Discovery, Prefix Discovery and interface address assignment
 | ([RFC4861]/[RFC4862]) except that the Router flag in Solicited
 | Neighbor Advertisement messages MUST be set to one if IP forwarding
 | is enabled; otherwise it MUST be set to zero ([RFC4861] Section 7.2.4).

-- Hiroki

---

From: "Wes Beebee (wbeebee)" <[email-masked]>
Date: Wed, 4 Nov 2009 13:37:51 -0500

> Thank you for the clarification.  Correct me if I am wrong, but in my
understanding, for router
> discovery and SLAAC the node must  accept/process RAs and must discard
received RSes.  This means 
> "acting as a host", but is there a technical reason to always set
R-bit in NAs zero?  A CE router
> has a moment of transition from a  host to a router (after
provisioning, for example) and vice
> versa as  viewed from the PE router, so making R-bit depend on whether
IP  forwarding is enabled
> or not still seems reasonable to me.

-----------------------------------------------------------------------
> When the router is attached to the WAN interface link it must act as 
> an IPv6 host for the purposes of Neighbor Discovery[RFC4861] and IPv6 
> Stateless Address Autoconfiguration[RFC4862].  The router acts as a
requesting router for the purposes of DHCP prefix delegation
([RFC3633]).

And, obviously, the router routes traffic out the WAN interface and does
NOT use the Conceptual Sending Algorithm of Neighbor Discovery to do so,
but rather a proper routing table.  The LAN interface acts as a router
when sending RA's, but both the WAN and LAN act as a host when the
router is being configured (e.g. with SNMP/HTTP).  The LAN port acts as
a router for the purposes of IPv6 SLAAC even though the WAN port acts as
a host.

So, as you can see, a CPE Router is both a router and a host on its WAN
interface.

- Wes

---

From: Ole Troan <[email-masked]>
Date: Wed, 4 Nov 2009 21:02:40 +0100

Hiroki,

[...]

>  forwarding is enabled or not still seems reasonable to me.

I don't think you can say that there is a transition from a host to a
router. it is performing functions of both at the same time, all the
time. e.g it will continue to process received RAs as long as the
interface is up...

>  to disable the functionality.

to turn the question around, why would you want to enable the flag?
for these types of links it is unlikely to be another host there, even
so I would avoid any situation where a host on the WAN link would end
up using the CE router as its default router.

the IPv6 CE router MUST not send RA messages on the WAN interface of
course, nor enable any routing protocol to attract traffic.

>  | is enabled; otherwise it MUST be set to zero ([RFC4861] Section 7.2.4).

Best regards,
Ole