Re: [ipwave] [Int-dir] Intdir early review of draft-ietf-ipwave-ipv6-over-80211ocb-34 -subnet structure, multicast

[Alexandre Petrescu <[e-mail]>]

Pascal,

Please allow me to change the subject of this, to reflect the content.
It helps tracking the discussion.

Le 11/04/2019 à 04:36, Pascal Thubert (pthubert) a écrit :
> Hello Brian
> 
> I meant broadcast at layer 2 not layer 3. L3 uses multicast but it 
> requires a service at the lower layer to implement it. This is rarely
> if ever a real L2 multicast service.

I can agree.

> IOW the IETF has thrown the problem over the fence to the IEEE but
> it is not really solved to this day.

I think indeed there is redirection of responsability to IEEE.  Maybe
IEEE does not like to do it, because of some reasons.

With respect to link-layer multicast: there is indeed no IEEE messaging
for creation or removal of link-layer multicast groups (like in IP there
is MLDv2).  But there is concept of link-layer multicast groups at IEEE.
  This is used extensively by mapping IP groups into link-layer groups,
and it helps IP.

Should IEEE develop a mechanism using messages (not just local filters)
for creating these link-layer groups?

> In practice, the service that is performed on IEEE std 802.3 is a 
> broadcast over a broadcast domain, and the subnet has to be contained
> within that domain.

Well yes and no.

Yes it is a broadcast  on 802.3 if we talk IPv4, but it is still
link-layer multicast on 802.3 if we talk IPv6: the link-layer addresses
ofIPv6 on Ethernet are link-layer multicast addresses.

> The broadcast operation is emulated on IEEE std 802.11 by the BSS
> operation whereby the AP reflects the message to be broadcasted, so
> the broadcast domain is that of the AP as opposed to that of the
> source STA.

I agree.

> By the proposed definition, if car A sees car B they are in the same
>  subnet. If car B sees car C they are in the same subnet. 
> Transitively Car A is in the same subnet as car C.

PAscal, again, this depends on how you set up the OCB interfaces on cars
A, B and C.

There are two options:
- use a single OCB interface with antenna sitting on top of each
   automobile.  Make them all in the same channel frequency (e.g. CCH -
   Control Channel).  That indeed has that A-B-C transitivity aspect.
   Worse, it has scalability issues: one cant grow a convoy beyond a few
   tens of meters and be sure the frontmost talks directly to the
   rearmost.  One never knows whether somebody in the middle repeats, or
   not.  Or one needs to  rely on MANET protocols that may forward on a
   single interface.  It has some PHY issues as well, that I can
   describe.  The powerpoint is readily filled with my last PHY
   experiments of propagation.
- use multiple OCB antennas situated at some strategic places in a car.
   This is in the same way as when placing the other ultra sound, radar
   and lidar sensors in the automobile.

   An OCB interface in the front bumper of one car forms a subnet with
   another OCB interface in the rear bumper of another car, on a
   particular channel (SCHx - service channel number x).  The front and
   rear subnets of a car are in distinct channels.  There is no A-B-C
   transitivity.  There is IP forwarding between front and rear
   interfaces of a car.

This can be described.  But I dont think it should be described in the
IP-over-OCB document.  It is a PHY MAC setting for OCB.

> But car C may not be in the radio broadcast domain of car A, and
> there is no BSS by definition of OCB to emulate a broadcast domain
> between them via an AP. End result is that a DAD or a lookup by car A
> will not reach car C.

That may be true, but it is true mostly in a setting where each car uses
a single OCB interface whose antenna is placed on the roof of the car
(placed at same place as the the GPS, LTE, FM or DVB-T antennas are placed).

In settings where each car has multiple OCB interfaces and multiple
antennas placed at strategic places (strategic: places that are relevant
to PHY propagation conditions), rather than simply on the roof, the
issue you describe in the above paragraph.

Now, if you read up to here, I would like to ask you (without claiming
to be all-knowing), whether you think a car could have several OCB
interfaces?

> By traditional MANET and 6lo definition, the radio broadcast domain 
> of a node is his link.

It is good, and I agree with it.

For my part, I do not use the traditional MANET and 6lo definitions
because I believe they are not sufficient for vehicular environments.

> In you lab you can arrange that the broadcast domains of 3 cars fully
> overlap.

I agree, people do that.  It is in small lab, with size in the range of
a few meters; there is much reflexion from the walls.  It is not outdoors.

> In that case, the link appears to match the common sense of a link in
> wires and the classical IPv6 operations will work pretty much the
> same as in a BSS over that Link. It is for example easy to place a
> subnet that matches that Link. It is also easy to confuse a Link with
> a Subnet, which is what the definition does. As soon as the broadcast
> domains start diverging, things get hairy, see all the work by Erik
> about split subnet etc...

I fully agree with this paragraph.

I think if one puts several interfaces and antennas in a car, and
carefully design the use of the propagation models (e.g. avoid 'omni',
consider 'directional', etc) then one can avoid many problems forbidding
IP from running on wireless.

> The IETF has studied this situations for 10+ years at MANET, 6TiSCH 
> and 6lo. We have an architecture that cover single link and multilink
> subnets.

Yes, there is.

> In the former case, the link is defined by one node that owns the
> prefix. In the latter case, routing is required inside the subnet and
> we created RPL to cover the situation.

YEs, but these are departures from what might be called traditional IP
forwarding.  That forwarding happens between two distinct interfaces.

In practice it means little software for MANET-6lo-multilink is publicly
available, and the engineer skill about them is hard to find.  This
translates to equipment being very expensive.

I want to tell you that communication equipment for cars is already very
high compared to an off-the-shelf WiFi router.  That high price tag is
due also to specification of things that are too intelligent and that
require high skills from few people.  This is the case of V2X stacks
doing ETSI CAM with GeoNetworking and similar.  You end up with a
3000Eur IP-OBU when its underlying hardware with linux and traditional
IP forwarding costs around 700Eur.

To that 3000Eur one may need to add costs of complexity of MANET
protocols and 6lo multilink subnet moels you arrive at a cost per
communication box that is the equivalent of a small car.

This high cost is less and less acceptable.

Compare that to the 1Eur LTE-WiFi dongle retrofitted recently in some cars.

> We created RFC 8505 for an host to connect to the network in either 
> situation, without the requirement that the L2 broadcast domain of 
> the host (its Link) overlaps with that of other nodes in the subnet 
> (because they don't). We have made RFC 8505 abstract to the routing 
> protocol if any, IOW without the requirement that the host knows 
> there is a MLSN, understands RPL or whatever other routing is used

MLSN?

> to put together the MLSN. To get there we had to abandon the
> dependency that a L2 broadcast from the host reaches all nodes in the
> subnet, IOW that the subnet is contained within the Link of all of

IOW?

> its members, IOW that the Links of all the nodes in the subnet fully 
> overlap. This meant we had to abandon the idea of using multicast in 
> ND for DAD and AR.
> 
> Maybe someone can explain that better than I did. I so please be my 
> guest. I really tried but I'm not convinced I did not waste my time 
> with the authors of the draft.

You did not waste your time, no more than I did.

Alex

> 
> All the best,
> 
> Pascal
> 
>> -----Original Message----- From: Int-dir <[e-mail]>
>> On Behalf Of Brian E Carpenter Sent: jeudi 11 avril 2019 09:54 To:
>> NABIL BENAMAR <[e-mail]>; Pascal Thubert (pthubert)
>>  <[e-mail]> Cc: [e-mail]; [e-mail]; 
>> [e-mail]; draft-ietf-ipwave-ipv6-over- 
>> [e-mail]; Alexandre Petrescu 
>> <[e-mail]>; Ole Troan <[e-mail]> 
>> Subject: Re: [Int-dir] Intdir early review of 
>> draft-ietf-ipwave-ipv6-over- 80211ocb-34 - 'conforming IPv6' - 
>> fe80::/10 vs fe80::/64
>> 
>> Hi Nabil,
>> 
>> On 11-Apr-19 03:40, NABIL BENAMAR wrote:
>>> Do we still talk about broadcast in IPv6 ?
>> 
>> No, we talk about multicast. Pascal was using shorthand. But if 
>> multicast fails with high probability, several aspects of IPv6 will
>> fail too, unless the LAN provides an NBMA (non-broadcast multiple
>> access) emulation of multicast, or suitable alternatives to SLAAC,
>> ND, NUD, and RA.
>> 
>> An earlier draft of this spec mentioned this problem:
>> 
>>>>> The operation of the Neighbor Discovery protocol (ND) over 
>>>>> 802.11-OCB links is different than over 802.11 links.  In 
>>>>> OCB, the link layer does not ensure that all associated 
>>>>> members receive all messages, because there is no association
>>>>> operation.  Neighbor Discovery (ND) is used over 802.11-OCB.
>> 
>> but it was inconsistent and was removed. If Ole is correct below 
>> about real-life conditions, the *problem* was not removed and the 
>> draft is not going to work in the real world.
>> 
>> Brian
>> 
>>> 
>>> On Wed, Apr 10, 2019, 14:45 Pascal Thubert (pthubert)
>> <[e-mail] <mailto:[e-mail]>> wrote:
>>> 
>>> Hello Ole:
>>> 
>>> Better remove, it is wrong anyway.
>>> 
>>> Because it is transitive, the description extends the so-called 
>>> subnet step
>> by step to a potentially large number of cars such that there is no
>> broadcast domain that covers them all. If there is no broadcast 
>> domain and no multicast emulation like a BSS does, how can we run 
>> ND? Yes, it works with 3 cars in a lab.
>>> 
>>> The description looks like it is confused with the MANET / 
>>> 6LoWPAN
>> concept of link, whereby my link joins the collection of nodes that
>> my radio can reach.
>>> 
>>> All the best,
>>> 
>>> Pascal
>>> 
>>>> -----Original Message----- From: Ole Troan 
>>>> <[e-mail]
>> <mailto:[e-mail]>>
>>>> Sent: mercredi 10 avril 2019 20:41 To: Alexandre Petrescu 
>>>> <[e-mail]
>> <mailto:[e-mail]>>
>>>> Cc: Pascal Thubert (pthubert) <[e-mail]
>> <mailto:[e-mail]>>; [e-mail] 
>> <mailto:[e-mail]>;
>>>> [e-mail] <mailto:[e-mail]>; [e-mail] 
>>>> <mailto:int-
>> [e-mail]>; draft-ietf-ipwave-ipv6-over-
>>>> [e-mail] <mailto:[e-mail]>; Brian E
>> Carpenter <[e-mail] 
>> <mailto:[e-mail]>>
>>>> Subject: Re: [Int-dir] Intdir early review of 
>>>> draft-ietf-ipwave-ipv6-over- 80211ocb-34 - 'conforming IPv6' -
>>>>  fe80::/10 vs fe80::/64
>>>> 
>>>>> You said: if OCB is still 48bit, and if there is bridging 
>>>>> OCB-Ethernet, then
>> no
>>>> reason to be different than rfc2464.
>>>>> 
>>>>> I said: OCB is still 48bit, but there is no bridging 
>>>>> OCB-Ethernet.
>>>>> 
>>>>> The conclusion is: there is reason to be different from RFC 
>>>>> 2464.
>>>> 
>>>> Why?
>>>> 
>>>>> Now, you give a different conclusion.
>>>>> 
>>>>> Excuse me, I would like to clarify this please?
>>>> 
>>>> Clarify what? That a link-layer that looks an awfully lot like
>>>>  Ethernet should not follow
>> the
>>>> 64-bit boundary and the definition of the link-local address 
>>>> mapping of rfc2464? Section 4.5.1 is already clear on that.
>>>> 
>>>> I think the only thing we are asking you is to change the 
>>>> following
>> paragraph:
>>>> 
>>>> OLD: A subnet is formed by the external 802.11-OCB interfaces 
>>>> of vehicles that are in close range (not by their in-vehicle 
>>>> interfaces).  This subnet MUST use at least the link-local 
>>>> prefix fe80::/10 and the interfaces MUST be assigned IPv6 
>>>> addresses of type link-local.
>>>> 
>>>> NEW: A subnet is formed by the external 802.11-OCB interfaces 
>>>> of vehicles that are in close range (not by their in-vehicle 
>>>> interfaces). A node MUST form a link-local address on this 
>>>> link.
>>>> 
>>>> Not quite sure what value that paragraph adds in the first 
>>>> place. You
>> could
>>>> probable remove it.
>>>> 
>>>> Cheers, Ole
>>>> 
>>>> 
>>>>> 
>>>>> Alex
>>>>> 
>>>>> Le 10/04/2019 à 12:28, Ole Troan a écrit :
>>>>>> Alexandre, Right, so it doesn’t sound like you have any 
>>>>>> reason to be different
>> from
>>>> RFC2464.
>>>>>> Just reference or copy that text (section 5, rfc2464). Ole
>>>>>>> On 10 Apr 2019, at 11:22, Alexandre Petrescu
>>>> <[e-mail]
>> <mailto:[e-mail]>> wrote:
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> Le 10/04/2019 à 11:04, Ole Troan a écrit :
>>>>>>>>>>>> "At least" does not mean "the value should be 
>>>>>>>>>>>> at least 10" in
>> that
>>>> phrase.
>>>>>>>>>>>> 
>>>>>>>>>>>> Do you think we should say otherwise?
>>>>>>>>>>> 
>>>>>>>>>>> To me there is nothing in the actual text to tell
>>>>>>>>>>> me that "at
>> least"
>>>>>>>>>>> qualifies the "/10". I think you could rephrase 
>>>>>>>>>>> as "This subnet's prefix MUST lie within the 
>>>>>>>>>>> link-local prefix fe80::/10 ..."
>>>>>>>>>>> 
>>>>>>>>>>> However, see Jinmei's messages about conformance
>>>>>>>>>>>  with RFC
>> 4291.
>>>>>>>>>>> 
>>>>>>>>>>> I think there might be unexpected side effects 
>>>>>>>>>>> from using an address like fe80:1::1. What if 
>>>>>>>>>>> some code uses matching with fe80::/64 to test if
>>>>>>>>>>> an address is link-local? I agree that would be
>>>>>>>>>>> faulty code, but you would be the first to 
>>>>>>>>>>> discover it.
>>>>>>>>>> Indeed. If you absoultely must cut and paste text 
>>>>>>>>>> from 2464:
>>>>>>>>> 
>>>>>>>>> YEs, that is how we started.  We cut and paste from 
>>>>>>>>> 2464.
>>>>>>>>> 
>>>>>>>>>> 5.  Link-Local Addresses The IPv6 link-local 
>>>>>>>>>> address [AARCH] for an Ethernet interface is formed
>>>>>>>>>> by appending the Interface Identifier, as defined
>>>>>>>>>> above,
>> to
>>>>>>>>>> the prefix FE80::/64. 10 bits            54 bits
>>>>>>>>>> 64 bits 
>>>>>>>>>> +----------+-----------------------+----------------------------+
>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> 
>>>>>>> |1111111010|         (zeros)       |    Interface 
>>>>>>> Identifier    |
>>>>>>>>>> 
>>>>>>>>>> +----------+-----------------------+----------------------------+
>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> 
>>>>>>> 
>>>>>>>>>> I presume there is support for bridging 802.11p and
>>>>>>>>>> other 802.3
>> links?
>>>>>>> 
>>>>>>> In the IP-OBUs that I know there is IP forwarding between
>>>>>>> 802.11-
>> OCB
>>>> (earlier 802.11p) and 802.3, not bridging.
>>>>>>> 
>>>>>>> In some IP-OBU (Internet Protocol On-Board Unit) some 
>>>>>>> non-OCB
>>>> interfaces are indeed bridged.  E.g. the Ethernet interface is
>>>>  bridged to
>> the
>>>> WiFi interface; that helps with DHCP, tcpdump and others to see
>>>> one a
>> single -
>>>> bridged - interface.
>>>>>>> 
>>>>>>> Bridging may be, but it is not a MUST.  There is no 
>>>>>>> necessarily any
>> bridging
>>>> between the 802.11-OCB interface and other interface, neither 
>>>> bridging between the multiple 802.11-OCB interfaces that might
>>>>  be present in
>> the
>>>> same computer.
>>>>>>> 
>>>>>>> Do you assume bridging of 802.11-OCB interface to 
>>>>>>> Ethernet
>> interface is
>>>> always there?
>>>>>>> 
>>>>>>> Note: I also heard many comments suggesting that EAL is 
>>>>>>> akin to
>>>> 'bridging'.  I do not know whether you refer to that 
>>>> perspective.  If yes,
>> we can
>>>> discuss it separately.
>>>>>>> 
>>>>>>> Alex
>>>>>>> 
>>>>>>> [...]
>>>>>>> 
>>>>>>>>>> And that the MAC address length of this link type 
>>>>>>>>>> is also 48 bits?
>>>>>>>>> 
>>>>>>>>> YEs, the length of MAC address on 802.11 mode OCB is
>>>>>>>>>  also 48.
>>>>>>>>> 
>>>>>>>>>> If the two assumptions above hold, then I see zero
>>>>>>>>>>  justification
>> for
>>>> pushing the 64 bit boundary in this draft.
>>>>>>>>> 
>>>>>>>>> Let me try  to understand the first assumption.
>>>>>>>> Ole
>>>>>>> 
>>>>>>> _______________________________________________ Int-dir 
>>>>>>> mailing list [e-mail] <mailto:[e-mail]> 
>>>>>>> https://www.ietf.org/mailman/listinfo/int-dir
>>>>> 
>>>>> _______________________________________________ Int-dir 
>>>>> mailing list [e-mail] <mailto:[e-mail]> 
>>>>> https://www.ietf.org/mailman/listinfo/int-dir
>>> 
>> 
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