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Message-ID: <8c92838a-4830-581d-c46d-08e399128f0f@blackwall.org> Date: Mon, 13 Nov 2023 12:00:04 +0200 From: Nikolay Aleksandrov <razor@...ckwall.org> To: Hangbin Liu <liuhangbin@...il.com>, netdev@...r.kernel.org Cc: "David S . Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Ido Schimmel <idosch@...sch.org>, Roopa Prabhu <roopa@...dia.com>, Stephen Hemminger <stephen@...workplumber.org>, Florian Westphal <fw@...len.de>, Andrew Lunn <andrew@...n.ch>, Florian Fainelli <f.fainelli@...il.com>, Vladimir Oltean <olteanv@...il.com>, Jiri Pirko <jiri@...nulli.us> Subject: Re: [RFC PATCHv3 net-next 07/10] docs: bridge: add multicast doc On 11/10/23 12:15, Hangbin Liu wrote: > Add multicast part for bridge document. > > Signed-off-by: Hangbin Liu <liuhangbin@...il.com> > --- > Documentation/networking/bridge.rst | 55 +++++++++++++++++++++++++++++ > 1 file changed, 55 insertions(+) > > diff --git a/Documentation/networking/bridge.rst b/Documentation/networking/bridge.rst > index 88dfc6eb0919..1fe645c9543d 100644 > --- a/Documentation/networking/bridge.rst > +++ b/Documentation/networking/bridge.rst > @@ -164,6 +164,61 @@ on bridge is disabled by default. After enabling VLAN > filter on bridge, the bridge can handle VLAN-tagged frames and forward them > to the appropriate destinations. > > +Multicast > +========= > + > +The Linux bridge driver has multicast support allowing it to process Internet > +Group Management Protocol (IGMP) or Multicast Listener Discovery (MLD) > +messages, and to efficiently forward multicast data packets. The bridge > +driver support IGMPv2/IGMPv3 and MLDv1/MLDv2. > + > +Multicast snooping > +------------------ > + > +Multicast snooping is a networking technology that allows network switches > +to intelligently manage multicast traffic within a local area network (LAN). > + > +The switch maintains a multicast group table, which records the association > +between multicast group addresses and the ports where hosts have joined these > +groups. The group table is dynamically updated based on the IGMP/MLD messages > +received. With the multicast group information gathered through snooping, the > +switch optimizes the forwarding of multicast traffic. Instead of blindly > +broadcasting the multicast traffic to all ports, it sends the multicast > +traffic based on the destination MAC address only to ports which have joined > +the respective destination multicast group. > + > +When created, the Linux bridge devices have multicast snooping enabled by > +default. It maintains a Multicast forwarding database (MDB) which keeps track > +of port and group relationships. > + > +IGMPv3/MLDv2 ETH support s/ETH/EHT/ Explicit Host Tracking is what we use in the bridge. I know both are correct, but we should be consistent. You can change it below as well. > +------------------------ > + > +The Linux bridge supports IGMPv3/MLDv2 ETH (Explicit Tracking of Hosts), which > +was added by `474ddb37fa3a ("net: bridge: multicast: add EHT allow/block handling") > +<https://lore.kernel.org/netdev/20210120145203.1109140-1-razor@blackwall.org/>`_ > + > +The explicit tracking of hosts enables the device to keep track of each > +individual host that is joined to a particular group or channel. The main > +benefit of the explicit tracking of hosts in IGMP is to allow minimal leave > +latencies when a host leaves a multicast group or channel. > + > +The length of time between a host wanting to leave and a device stopping > +traffic forwarding is called the IGMP leave latency. A device configured > +with IGMPv3 or MLDv2 and explicit tracking can immediately stop forwarding > +traffic if the last host to request to receive traffic from the device > +indicates that it no longer wants to receive traffic. The leave latency > +is thus bound only by the packet transmission latencies in the multiaccess > +network and the processing time in the device. > + > +Other multicast features > +------------------------ > +The Linux bridge also supports `per-VLAN multicast snooping > +<https://lore.kernel.org/netdev/20210719170637.435541-1-razor@blackwall.org/>`_, > +which is disabled by default but can be enabled. And `Multicast Router Discovery > +<https://lore.kernel.org/netdev/20190121062628.2710-1-linus.luessing@c0d3.blue/>`_, > +which help identify the location of multicast routers. > + > FAQ > === >
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