linux-kernel - Re: [RFC net-next 2/3] net: dsa: qca8k: enable assisted learning on CPU port

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Date:   Tue, 10 Aug 2021 19:27:05 +0200
From:   Andre Valentin <avalentin@...cant.net>
To:     DENG Qingfang <dqfext@...il.com>,
        Vladimir Oltean <olteanv@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        "open list:NETWORKING DRIVERS" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Ansuel Smith <ansuelsmth@...il.com>,
        Jonathan McDowell <noodles@...th.li>,
        Michal Vokáč <vokac.m@...il.com>,
        Christian Lamparter <chunkeey@...il.com>,
        Nishka Dasgupta <nishkadg.linux@...il.com>,
        John Crispin <john@...ozen.org>,
        Stefan Lippers-Hollmann <s.l-h@....de>,
        Hannu Nyman <hannu.nyman@....fi>,
        Imran Khan <gururug@...il.com>,
        Frank Wunderlich <frank-w@...lic-files.de>,
        Nick Lowe <nick.lowe@...il.com>
Subject: Re: [RFC net-next 2/3] net: dsa: qca8k: enable assisted learning on
 CPU port

On Sun, Aug 08, 2021 at 1805, DENG Qingfang wrote:
> On Sun, Aug 08, 2021 at 01:25:55AM +0300, Vladimir Oltean wrote:
>> On Sat, Aug 07, 2021 at 08:07:25PM +0800, DENG Qingfang wrote:
>>> Enable assisted learning on CPU port to fix roaming issues.
>>
>> 'roaming issues' implies to me it suffered from blindness to MAC
>> addresses learned on foreign interfaces, which appears to not be true
>> since your previous patch removes hardware learning on the CPU port
>> (=> hardware learning on the CPU port was supported, so there were no
>> roaming issues)

The issue is with a wifi AP bridged into dsa and previously learned
addresses.

Test setup:
We have to wifi APs a and b(with qca8k). Client is on AP a.

The qca8k switch in AP b sees also the broadcast traffic from the client
and takes the address into its fdb.

Now the client roams to AP b.
The client starts DHCP but does not get an IP. With tcpdump, I see the
packets going through the switch (ap->cpu port->ethernet port) and they
arrive at the DHCP server. It responds, the response packet reaches the
ethernet port of the qca8k, and is not forwarded.

After about 3 minutes the fdb entry in the qca8k on AP b is
"cleaned up" and the client can immediately get its IP from the DHCP server.

I hope this helps understanding the background.