netdev - Re: [RFC PATCH net-next 00/13] vxlan: Add MDB support

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Message-ID: <0a820f10-f10f-64b7-14ba-58d9337cbb69@blackwall.org>
Date:   Tue, 7 Feb 2023 22:02:58 +0100
From:   Nikolay Aleksandrov <razor@...ckwall.org>
To:     Ido Schimmel <idosch@...dia.com>
Cc:     netdev@...r.kernel.org, bridge@...ts.linux-foundation.org,
        davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        edumazet@...gle.com, roopa@...dia.com, petrm@...dia.com,
        mlxsw@...dia.com
Subject: Re: [RFC PATCH net-next 00/13] vxlan: Add MDB support

On 2/7/23 11:25, Ido Schimmel wrote:
> On Tue, Feb 07, 2023 at 12:24:25AM +0100, Nikolay Aleksandrov wrote:
>> Hmm, while I agree that having the control plane in user-space is nice,
>> I do like having a relatively straight-forward and well maintained
>> protocol implementation in the kernel too, similar to its IGMPv3 client
>> support which doesn't need third party packages or external software
>> libraries to work. That being said, I do have (an unfinished) patch-set
>> that adds a bridge daemon to FRR, I think we can always add a knob to
>> switch to some more advanced user-space daemon which can snoop.
>>
>> Anyway to the point - this patch-set looks ok to me, from bridge PoV
>> it's mostly code shuffling, and the new vxlan code is fairly straight-
>> forward.
> 
> Thanks for taking a look. I was hoping you would comment on this
> section... :)
>

:)

> After sending the RFC I realized that what I wrote about the user space
> implementation is not accurate. An AF_PACKET socket opened on the VXLAN
> device will only give you the decapsulated IGMP / MLD packets. You
> wouldn't know from which remote VTEP they arrived. However, my point
> still stands: As long as the kernel is not performing snooping we can
> defer the forming of the replication lists to user space and avoid the
> complexity of the "added_by_star_ex" entries (among many other things).
> If in the future we need to implement snooping in the kernel, then we
> will expose a new knob (e.g., "mcast_snooping", default off), which will
> also enable the "added_by_star_ex" entries.
> 

Yep, I agree that it would be best for this case and we don't need the 
extra complexity in the kernel. I was referring more to the standard
IGMPv3 implementation (both client and bridge).

> I tried looking what other implementations are doing and my impression
> is that by "VXLAN IGMP snooping" they all refer to the snooping done in
> the bridge driver. That is, instead of treating the VXLAN port as a
> router port, the bridge will only forward specific groups to the VXLAN
> port, but this multicast traffic will be forwarded to all the VTEPs.
> This is already supported by the kernel.
> 
> Regarding what you wrote about a new knob in the bridge driver, you mean
> that this knob will enable MDB lookup regardless of "mcast_snooping"?

Yep, we can implement the snooping logic in user-space and use the
bridge only as a dataplane (that's what my bridge daemon in frr was
going to do for IGMPv3 and also explicit host tracking).

> Currently this knob enables both snooping and MDB lookup. Note that I
> didn't add a new knob to the VXLAN device because I figured that if user
> space doesn't want MDB lookup, then it will not configure MDB entries.
>

Yeah, of course. The set makes sense as it is since vxlan's logic would
be in user-space.

> Thanks!