IPv6 - NS, DAD and MLDv2 interaction

From: Scheffenegger, Richard <Richard.Scheffenegger_at_netapp.com>
Date: Wed, 23 Feb 2022 13:46:32 UTC

I hope someone more knowledgeable then me in IPv6 affairs can give an informed opinion on the following:

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”.

However, IPv6 Multicast addresses are largely indendent of the above protocols (afaik) and can be freely defined in the IPv6 address space. A “proper” (non-local) IPv6 multicast is formed by a Host registering via MLD, and again mapping packets destinged to a partical IPv6 multicast group into a similarly formed Ethernet MAC 33-33-xx-xx-xx-xx.

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.

A bit similar to IGMP snooping, with the difference that in v4, crucial basic information was exchanged using Eth broadcasts (ARP) rather than Eth Multicasts which look alike “data” IPv6 multicast.

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…

Best regards,