Bridges and ethernet multicast packet flooding?

Question

Sanity check:If I have an unmanaged bridge (or, in this case, a wireless client-to-ethernet adapter, connects to a wifi network,allows hardware with ethernet plug to be connected to thewifi network), is such a device required to pass all ethernetmulticast traffic? Case in point: I have such a device, the wifi network supportsIPv6 native, and and the (wired) device doesn't see anyIPv6 traffic - no Router Advertizements, ND doesn't work, etc. A friend suggested IGMP but that's not for IPv6 RA and ND packets, yes?Confued,Geert Jan

Albert Manfredi · Accepted Answer

IPv6 does not use IGMP. It uses MLD instead (multicast listener discovery).

But similar to IPv4, there are a set of multicast addresses that hosts are supposed to receive at al times, and there is also something called a "solicited node multicast address," based on the host's unicast address, that the host is supposed to receive at all times.

See RFC 4291 for the list of required multicast addresses, and RFC

2710 for MLDv1 (like IGMPv2).

The Ethernet addresses for IPv6 are mapped to 0x33-33-the bottom four bytes of the IPv6 multicast address.

So, there are some things to check out. Are both hosts IPv6? Are the layer 2 devices in the path doing IGMP snooping? That would be a bad thing in this case, because they may be blocking IPv6 multicasts that should never be blocked, i.e. those described in RFC 4291.

Bert

Bridges and ethernet multicast packet flooding?

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