[PATCHv3,net-next,07/10] docs: bridge: add multicast doc

Commit Message

Hangbin Liu Nov. 28, 2023, 8:49 a.m. UTC

Add multicast part for bridge document.

Acked-by: Nikolay Aleksandrov <[e-mail]>
Signed-off-by: Hangbin Liu <[e-mail]>
---
 Documentation/networking/bridge.rst | 55 +++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

Comments

Florian Fainelli Nov. 29, 2023, 4:15 a.m. UTC | #1

On 11/28/2023 12:49 AM, Hangbin Liu wrote:
> Add multicast part for bridge document.
> 
> Acked-by: Nikolay Aleksandrov <[e-mail]>
> Signed-off-by: Hangbin Liu <[e-mail]>
> ---
>   Documentation/networking/bridge.rst | 55 +++++++++++++++++++++++++++++
>   1 file changed, 55 insertions(+)
> 
> diff --git a/Documentation/networking/bridge.rst b/Documentation/networking/bridge.rst
> index 764d44c93c65..956583d2a184 100644
> --- a/Documentation/networking/bridge.rst
> +++ b/Documentation/networking/bridge.rst
> @@ -161,6 +161,61 @@ on a bridge is disabled by default. After enabling VLAN filtering on a bridge,
>   it will start forwarding frames to appropriate destinations based on their
>   destination MAC address and VLAN tag (both must match).
>   
> +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.

nit: supports.

> +
> +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.

maybe s/joined/subscribed/g (throughout the whole document)? Other than 
that:

Reviewed-by: Florian Fainelli <[e-mail]>

Patch

diff --git a/Documentation/networking/bridge.rst b/Documentation/networking/bridge.rst
index 764d44c93c65..956583d2a184 100644
--- a/Documentation/networking/bridge.rst
+++ b/Documentation/networking/bridge.rst
@@ -161,6 +161,61 @@  on a bridge is disabled by default. After enabling VLAN filtering on a bridge,
 it will start forwarding frames to appropriate destinations based on their
 destination MAC address and VLAN tag (both must match).
 
+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 EHT support
+------------------------
+
+The Linux bridge supports IGMPv3/MLDv2 EHT (Explicit Host Tracking), which
+was added by `474ddb37fa3a ("net: bridge: multicast: add EHT allow/block handling")
+<https://lore.kernel.org/netdev/[e-mail]/>`_
+
+The explicit host tracking 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 host tracking 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/[e-mail]/>`_,
+which is disabled by default but can be enabled. And `Multicast Router Discovery
+<https://lore.kernel.org/netdev/[e-mail]/>`_,
+which help identify the location of multicast routers.
+
 FAQ
 ===