[riot-devel] Border-router and multicast

Alexander Aring alex.aring at gmail.com
Mon May 9 18:59:49 CEST 2016

On Mon, May 09, 2016 at 06:20:48PM +0200, Baptiste Clenet wrote:
> 2016-05-09 16:44 GMT+02:00 Alexander Aring <alex.aring at gmail.com>:
> > On Mon, May 09, 2016 at 04:24:34PM +0200, Baptiste Clenet wrote:
> >> Hi Martine,
> >> Thank you for the answer.
> >> Ok ff04::1 is also a multicast address so I add it to every board with
> >> gnrc_networking and I should be able to ping them with this multicast
> >> address.
> >> Shouldn't I use:
> >> ifconfig 7 add multicast ff04::1
> >> ?
> >>
> >> I'm missing something here, could give me an explanation please:
> >> Before, I had a transceiver plugged on my linux so I was able to ping
> >> my board directly using fe80::address so I was able to use the local
> >> multicast address ff02::1, now that I use border router, I'm using a
> >> prefix 2001::db8 (why? and why documentation prefix?) Why can't I use
> >> fe80 as before?
> >
> > because link-local ff80::/10 will not be routed, between lowpan and
> > ethernet interface, so far I know.
> ff80? You meant fe80? I was able to do ping with fe80 and lowpan0.


> >
> > I think what you want to have is the npd proxy magic stuff. See [0].
> > Just plugin the ethernet cable and your network will be extended with
> > the 6LoWPAN nodes.
> What I want is to understand a bit better how my network works.
> Each node is inside the same PAN (let's say 0x23 by default on RIOT,
> any reason why you choose 0x23?)
> RIOT starts and we affect an link-local address fe80 so every RIOT
> node can ping another one with its link-local address.
> Then comes border-router, border router will tell every node to add a
> new ip with prefix 2001:db8::, is this right?

For this you need radvd [0] which sends RA with PIO (prefix information

> How often does border router send a message to other node to say to
> add this new ip address?

depends on setting. Normally RA is a responds according to RS. RA can
also be transmitted periodically.

> Why 2001:db8 has been chosen? and how should I choose this prefix if I
> want to use my product for commercial use?
> Why can't I ping a link-local address from Linux with the border router?

Because fe80::/10 address scope will not be routed, you could do that I
think with the ndp proxy stuff. If you simple want to extend your
ethernet IPv6 network with the 6LoWPAN nodes, then I suppose ndp proxy
can do that.

> I've got ten nodes and one linux with a border router, what I want is
> to be able to send messages to each of them (or all of them by
> multicast) at any moment, here I don't understand why I should use
> global address 2001:db8 instead of fe80::

Because global addresses will be routed and are global? :-)

local is local in your network and global can be accessed from
"outside" and with "outside" I mean the internet, that's maybe the
reason why link-local will not be routed.

With a border router, you need to route from one IPv6 interface to
another IPv6 interface and link-local will not be routed over that.

NDP proxy is so far I know something where you can extend the network
from one IPv6 interface to another IPv6 interface but it's more some
tricky stuff to do this and maybe not everything is implemented what you

> Thanks for your time,

I hope I could help you.

- Alex

[0] https://github.com/linux-wpan/radvd/tree/6lowpan

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