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Re: how do I disable IPv6?

kre%munnari.OZ.AU@localhost (Robert Elz) writes:

>IPv6 DAD uses multicast (nothing in IPv6 uses broadcast), if WiFi
>is unable to do multicast, then it cannot implement half of the infrastructure
>of IPv6 - and I find that hard to believe.

A true WiFi multicast can only work at the lowest common speed of all devices,
it cannot work if devices don't have a common speed at all.

That's why multicast is mostly implemented by sending a packet to the access
point which then unicasts the data to each device individually. In that
specific environment it's much faster and occupies less 'air time' than
other solutions.

So, multicasting IP works fine. But you receive the replicated transmissions
from the access point, even when you are the original sender. With standard
DAD it's impossible to distinguish your DAD probes from other devices' DAD
probes, as everything is received from the access point (or even other
access points in case of roaming).

The topic is somewhat discussed in RFC 4862 Appendix A.

Standard DAD works on the IP layer, by merging in WiFi-specific information
(origin mac address) you could resolve the issue for WiFi, but maybe not for
other media.

A generic solution would be a nonce that is sent with a probe to detect the
looped back packet by checking its payload.

AFAIK, there were drafts about such extensions, but nothing standard.

There is also RFC4429 (I don't think we implement it) which would speed
up regular DAD but which would also need to be adapted to such special
WiFi extensions.

                                Michael van Elst
                                "A potential Snark may lurk in every tree."

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