netdev - Re: [patch net-next] mlxsw: spectrum_switchdev: Allow port enslavement to a VLAN-unaware bridge

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Date:   Wed, 21 Feb 2018 13:31:40 -0700
From:   David Ahern <dsahern@...il.com>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org,
        davem@...emloft.net, idosch@...lanox.com, mlxsw@...lanox.com
Subject: Re: [patch net-next] mlxsw: spectrum_switchdev: Allow port
 enslavement to a VLAN-unaware bridge

On 2/21/18 1:24 PM, Ido Schimmel wrote:
>>> Does it matter if you try IPv4 ping or if vlan_filtering is set 1?
>>> Unfortunately, I can't reproduce on my switch.
>>
>> Bring up the hosts and then reboot the switch. At that point I get no
>> host to host communication. As soon as I flap the port on host1 host3 to
>> host1 starts working.
>>
>> So it seems to be something about the initial boot state.
> 
> You didn't have IPv6 *and* IPv4 ping? I'm asking because it's possible
> host1 sent an MLD join to the Solicited-node multicast address before
> the bridge started listening, which means it didn't have a corresponding
> MDB entry.

The sim only configures IPv6, but it is not acting as an mcast router.
It's really a dummy setup -- bridge on the switch, ports connected to hosts.

> 
> Assuming your hosts aren't functioning as multicast routers and sending
> MLD queries and that you didn't configure them as mrouter ports on the
> switch, then when host3 sent a neighbour solicitation message to host1's
> Solicited-node multicast address it wasn't flooded to host3 which
> prevented ping from passing.
> 
> This also explains why it started working when you flapped the port on
> host1, as Linux generates MLD joins in these cases.
> 
> You can try to disable snooping:
> 
> # ip link set dev br0 type bridge mcast_snooping 0
> 
> Just a guess, but worth a try.

good guess. That change gets it working.