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Date:   Thu, 3 Jan 2019 15:26:03 -0800
From:   Randy Dunlap <>
To:     Florian Fainelli <>,
Subject: Re: [PATCH net-next v2] Documentation: networking: Clarify switchdev
 devices behavior


Comments below.

On 1/3/19 2:47 PM, Florian Fainelli wrote:
> This patch provides details on the expected behavior of switchdev
> enabled network devices when operating in a "stand alone" mode, as well
> as when being bridge members. This clarifies a number of things that
> recently came up during a bug fixing session on the b53 DSA switch
> driver.
> Signed-off-by: Florian Fainelli <>
> ---
> Changes in v2:
> - clarified a few parts about VLAN devices wrt. VLAN filtering and their
>   behavior during enslaving.
> Ido, hopefully this captures correctly what we just talked about this
> morning. Thanks!
>  Documentation/networking/switchdev.txt | 95 ++++++++++++++++++++++++++
>  1 file changed, 95 insertions(+)
> diff --git a/Documentation/networking/switchdev.txt b/Documentation/networking/switchdev.txt
> index 82236a17b5e6..c0218746a783 100644
> --- a/Documentation/networking/switchdev.txt
> +++ b/Documentation/networking/switchdev.txt
> @@ -392,3 +392,98 @@ switchdev_trans_item_dequeue()
>  If a transaction is aborted during "prepare" phase, switchdev code will handle
>  cleanup of the queued-up objects.
> +
> +Switchdev enabled network device expected behavior
> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> +
> +Below is a set of defined behavior that switchdev enabled network device must be

                                                                     devices must

> +adhering to.

   adhere to.

> +
> +Configuration less state
> +------------------------
> +
> +Upon driver bring up, the network devices must be fully operational, and the
> +backing driver must be configuring the network device such that it is possible

                  must configure the

> +to send and receive to this network device such that it is properly separate
> +from other network devices/ports (e.g: as is frequently with a switch ASIC).


> +How this is achieved is heavily hardware dependent, but a simple solution can
> +be to use per-port VLAN identifiers unless a better mechanism is available
> +(proprietary metadata for each network ports for instance).


> +
> +The network device must be capable of running a full IP protocol stack must be
> +working, including multicast, DHCP, IPv4/6, etc. If necessary, it should be

garbled?  too many verb phrases.

> +programming the appropriate filters for VLAN, multicast, unicast etc. The
> +underlying device driver must effectively be configured in a similar fashion to
> +what it would do when IGMP snooping is enabled for IP multicast over these
> +switchdev network devices and unsollicited multicast must be filtered as early


> +as possible into the hardware.
> +
> +When configuring VLANs on top of the network device, all VLANs must be working,
> +irrespective of the state of other network devices (e.g: other ports being part


> +of a VLAN aware bridge doing ingress VID checking). See below for details.
> +
> +Bridged network devices
> +-----------------------
> +
> +When a switchdev enabled network device is added as a bridge member, it should
> +not be disrupting any functionality of non-bridged network devices and they

   not disrupt any

> +should continue to behave as normal network devices. Depending on the bridge
> +configuration knobs below, the expected behavior is documented.
> +
> +VLAN filtering
> +~~~~~~~~~~~~~~
> +
> +The Linux bridge allows the configuration of a VLAN filtering mode (compile and
> +run time) which must be observed by the underlying switchdev network
> +device/hardware:
> +
> +- with VLAN filtering turned off: frames ingressing the device with a VID that
> +  is not programmed into the bridge/switch's VLAN table must be forwarded.
> +
> +- with VLAN filtering turned on: frames ingressing the device with a VID that is
> +  not programmed into the bridges/switch's VLAN table must be dropped.
> +
> +Non-bridged network ports of the same switch fabric must not be disturbed in any
> +way, shape or form by the enabling of VLAN filtering.
> +
> +VLAN devices configured on top of a switchdev network device (e.g: sw0p1.100)
> +which is a bridge port member must also observe the following behavior:
> +
> +- with VLAN filtering turned off, these VLAN devices must be fully functional
> +  since the hardware is allowed VID frames. Enslaving VLAN devices into the
> +  bridge might be allowed provided that there is sufficient separatation using


> +  e.g: a reserved VLAN ID (4095 for instance) for untagged traffic.


> +
> +- with VLAN filtering turned on, these VLAN devices should not be allowed to
> +  be created because they duplicate functionality/use case with the bridge's
> +  VLAN functionality.
> +
> +Because VLAN filtering can be turned on/off at runtime, the switchdev driver
> +must be able to re-configure the underlying hardware on the fly to honor the
> +toggling of that option and behave appropriately.
> +
> +A switchdev driver can also refuse to support dynamic toggling of the VLAN
> +filtering knob at runtime and require a destruction of the bridge device(s) and
> +a creation of new bridge device(s) with a different VLAN filtering value to
> +ensure VLAN awareness is pushed down to the HW.
> +
> +IGMP snooping
> +~~~~~~~~~~~~~
> +
> +The Linux bridge allows the configuration of IGMP snooping (compile and run
> +time) which must be observed by the underlying switchdev network device/hardware
> +in the following way:
> +
> +- when IGMP snooping is turned off, multicast traffic must be flooded to all
> +  switch ports within the same broadcast domain, including the CPU/management
> +  port of the switch (if handled separately).
> +
> +- when IGMP snooping is turned on, multicast traffic must be selectively flowing

                                                        must selectively flow

> +  to the appropriate network ports and not flood the entire switch, that must
> +  include the CPU/management port.
> +
> +Because IGMP snooping can be turned on/off at runtime, the switchdev driver must
> +be able to re-configure the underlying hardware on the fly to honor the toggling
> +of that option and behave appropriately.
> +
> +Similarly to VLAN filtering, if dynamic toggling of the IGMP snooping

missing something here??


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