netdev - Re: [PATCH v3 net-next 0/5] IGMP snooping for local traffic

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Message-ID: <20171109211315.GA22805@lunn.ch>
Date:   Thu, 9 Nov 2017 22:13:15 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>, idosch@...lanox.com,
        jiri@...lanox.com
Subject: Re: [PATCH v3 net-next 0/5] IGMP snooping for local traffic

On Thu, Nov 09, 2017 at 12:35:32PM -0800, Florian Fainelli wrote:
> +Ido, Jiri,
> 
> On 11/09/2017 12:21 PM, Andrew Lunn wrote:
> > On Thu, Nov 09, 2017 at 11:38:26AM -0800, Florian Fainelli wrote:
> >> On 11/09/2017 11:30 AM, Andrew Lunn wrote:
> >>>> This means that switchdev drivers won't ever have to treat a HOST_MDB
> >>>> notification any differently than a PORT_MDB notification
> >>>
> >>> No, they need to treat it very differently. 
> >>
> >> Allow me to rephrase, switchdev drivers will ignore HOST_MDB
> >> notifications because that does not resolve to something they can do
> >> something about.
> > 
> > Hi Florian
> > 
> > Yes, they can. In fact, if they want to support IGMP snooping on the
> > bridge interface, they have to. How else do they know to forward
> > traffic to the host?
> 
> On a switchdev fabric, you need to have at least one user-facing port be
> a member of the bridge, and when the switchdev driver configures that,
> it should just make the IGMP packets trap to the management interface
> such that they can be delivered from the port member to the bridge
> network device (br0). In that case, I don't really see why you would
> need to send a HOST_MDB message to a switchdev fabric, since that should
> be part of enslaving the port to the bridge in the first place and
> appropriately configure the management interface to get IGMP snooping,
> BDPU etc.

So your network is carrying gigabits of multicast traffic. Are you
saying it should all hit the host, so the bridge can throw it away?
No, it is much more efficient that the bridge tells the switch when it
is interested in a specific multicast group. I.e. it sends a HOST_MDB
request for the group. Only then will the switch start to send the
data for that group to the host.

     Andrew