Re: IPv6 - NS, DAD and MLDv2 interaction

From: Lutz Donnerhacke <>
Date: Wed, 23 Feb 2022 15:51:38 UTC
On Wed, Feb 23, 2022 at 01:46:32PM +0000, Scheffenegger, Richard wrote:
> As far as I know, an IPv6 host initially tries to perform Duplicate
> Address Detection, as well as Neighbor Discovery / Neighbor Solicitation.
> All of this typically works on Ethernet, by mapping into a well-known
> Ethernet multicast destination MAC “33-33-xx-xx-xx-xx”.

Yup. IPv6 replaced broadcast by multicast on the link layer.

> It appears that some vendors of switches have started to become overly
> restrictive in forwarding Ethernet Multicast, and only deliver these *after*
> a Host has registered itself to receive / participate in specific IPv6
> Multicast groups.

May you please drop an information about the vendor?
So that we can warn the community to buy those broken products.

> So far, I could not find any guidance (and with my lack of depth into
> IPv6, it is also unclear to me, if this would even be possible) if
> registering a host into a IPv6 MC group via MLDv2 in order for it to receive
> NS, ND, DAD is something that would be expected…

The host must join (using MLDv2) the multicast groups for all of its own
addresses to be reachable by Neighbor Discovery. This does not include the
standard RD group (IIRC).