netdev - Re: dsa: mv88e6xxx not receiving IPv6 multicast packets

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Date:   Mon, 16 Nov 2020 10:45:18 +0000
From:   "Tj (Elloe Linux)" <ml.linux@...oe.vision>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Vladimir Oltean <olteanv@...il.com>, netdev@...r.kernel.org,
        chris.packham@...iedtelesis.co.nz, f.fainelli@...il.com,
        marek.behun@....cz, vivien.didelot@...il.com, info <info@...ris.cz>
Subject: Re: dsa: mv88e6xxx not receiving IPv6 multicast packets

On 15/11/2020 17:27, Andrew Lunn wrote:

> So check if you have an IGMP querier in the network. If not, try
> turning it on in the bridge,
> 
> ip link set br0 type bridge mcast_querier 
Thankfully it turns out this is totally unrelated to Linux - our TP-Link
Jetstream T1600G-PS has some unfortunate default behaviour and a bug.

Specifically, we are operating an IPv6-only network and Layer 2 MLD
snooping was enabled and set to forward unknown multicast groups and as
such the switch should be broadcasting all multicast packets.

However, buried in the TP-Link manual there's a note that says:

"Note: IGMP Snooping and MLD Snooping share the setting of Unknown
Multicast Groups, so you have to enable IGMP Snooping globally on the L2
FEATURES > Multicast > IGMP Snooping > Global Config page at the same
time."

We hadn't enabled IGMP snooping since we don't use IPv4!

Many thanks for the help resolving this and apologies for mis-reporting it.