Re: On the "IPv6 Neighbor Discovery on Wireless Networks" draft

Hi Pascal,

On 25-Sep-19 21:22, Pascal Thubert (pthubert) wrote:
> Hello Nabil :
>  
> Many thanks for your questions and interest:
> 
>> 1- You say " But in reality, IPv6 multicast messages are typically broadcast on the wireless medium, and so they are processed by most of the wireless nodes over the subnet (e.g., the ESS fabric).” most, some or all nodes?
>  
> That’s most. Ideally a broadcast would reach all nodes, but on Wi-Fi there’s no retry for broadcast. When a node sends a broadcast packet, only a portion of the nodes actually get it.

My experience a few IETFs ago was that the chance of a given link-local multicast getting through was about 10%, even when the sending host was sitting next to the receiving host in the same room. On investigation, this was because the NOC's throttling policy in the switches was pretty strong, as you would expect for a network like the IETF's. By contrast, on my home network the chances seem to be close to 100%. So I think the text needs a YMMV warning, even if "most" is indeed typical. More below...

> Some miss it because they fail to decode the packet at the PHY layer, others because of throttling policies that drop the broadcast low in the stack to protect the battery. This is why DAD often fails to detect duplicates.
> 
>> 2- In the text you mentioned IEEE 802.11p. You need to replace it by IEEE 802.11-OCB since the 'p' is no more used by IEEE and it has been replaced by OCB. See https://tools.ietf.org/html/draft-ietf-ipwave-ipv6-over-80211ocb-52
> 
> Yes, I’ll fix that with the next revision.
>  
>> 3- I think there are some duplications in the text about the fact that ".... in all the cases in this specification, the Layer-3 multicast operation is always a MAC_Layer broadcast for the lack of a Layer-2 multicast operation that could handle a possibly very large number ofgroups in order to make the unicast efficient.." Already mentioned in the introduction section.
>  
> True, I’ll fix that too 😊
> 
>> 4- You mentionned the example of cars using RPL (Route-Over MLSN) I think that cars do not belong to LLNs category.
>  
> I would not argue about whether car networks are LLN or not, because I think that matters little: the bottom line is that RPL is a generic DV layer-3 protocol, agnostic of the particular links (the OF takes the hit)  and it is applicable beyond ultra-low power links. 
> 
> We have an implementation on ethernet for ANIMA. 

Have we seen that at a hackathon? The "victim" of the throttling I mentioned above was my prototype of the ANIMA GRASP protocol, but running unsecured over the raw layer 2 network.
I'd love to run it over a RPL substrate. (Reply off list if you prefer.)

   Brian

> The root of my work on RPL was actually for cars, if you’re aware of the nested NEMO problem. RPL optimizes the amount of control at the expense of a routing stretch when not talking to the root. This is good for lower power nodes because it saves energy. But this is also great for mobile nodes such as cars that really over one another to reach the internet, because RPL filters out what they do not want to know like which are all the other cars, what topology is built to reach out, and all the mobility that takes place between them.
> 
>  
> 
> Many tahks again for you excellent comments : )
> 
>  
> 
> Pascal
> 
>  
> 
> *From:*ipv6 <ipv6-bounces@ietf.org> *On Behalf Of *Nabil Benamar
> *Sent:* mardi 24 septembre 2019 23:06
> *To:* ipv6@ietf.org
> *Subject:* On the "IPv6 Neighbor Discovery on Wireless Networks" draft
> 
>  
> 
> 
> Hi Pascal,
> 
>  
> 
> I would like to ask you some questions about your interesting draft.
> 
>  
> 
> 1- You say " But in reality, IPv6 multicast
> 
>    messages are typically broadcast on the wireless medium, and so they
> 
>    are processed by most of the wireless nodes over the subnet (e.g.,
> 
>    the ESS fabric).
> 
>  
> 
> most, some or all nodes?
> 
>  
> 
> 2- In the text you mentioned IEEE 802.11p. You need to replace it by IEEE 802.11-OCB since the 'p' is no more used by IEEE and it has been replaced by OCB.
> 
> See https://tools.ietf.org/html/draft-ietf-ipwave-ipv6-over-80211ocb-52
> 
>  
> 
> 3- I think there are some duplications in the text about the fact that "....
> 
>    in all the cases in this specification, the Layer-3 multicast
> 
>    operation is always a MAC_Layer broadcast for the lack of a Layer-2
> 
>    multicast operation that could handle a possibly very large number ofgroups in order to make the unicast efficient.."
> 
> Already mentioned in the introduction section.
> 
>  
> 
> 4- You mentionned the example of cars using RPL (Route-Over MLSN)
> 
> I think that cars do not belong to LLNs category.
> 
>  
> 
>  
> 
> Yours.
> 
>  
> 
> Best regards
> 
> Nabil Benamar
> 
> -------------------
> 
> نبيل بنعمرو
> 
>  
> 
>  
> 
>  
> 
> 
> 
> 
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