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Date: Sat, 28 Oct 2023 01:03:47 +0200
From: Andrew Lunn <>
To: Florian Fainelli <>
Cc: Linus Walleij <>,
	Vladimir Oltean <>,
	"David S. Miller" <>,
	Eric Dumazet <>,
	Jakub Kicinski <>, Paolo Abeni <>,,
Subject: Re: [PATCH] dsa: tag_rtl4_a: Bump min packet size

On Fri, Oct 27, 2023 at 02:23:13PM -0700, Florian Fainelli wrote:
> You would want your subject to be:
> net: dsa: tag_rtl4_a: Bump min packet size
> On 10/27/23 13:21, Linus Walleij wrote:
> > It was reported that the "LuCI" web UI was not working properly
> > with a device using the RTL8366RB switch. Disabling the egress
> > port tagging code made the switch work again, but this is not
> > a good solution as we want to be able to direct traffic to a
> > certain port.
> > 
> > It turns out that sometimes, but not always, small packets are
> > dropped by the switch for no reason.
> And we are positive that the Ethernet MAC is also properly padding frames
> before having them ingress the switch?

It might be interesting to run a script which systematically does a
ping, or similar, for all frame sizes.

> > If we pad the ethernet frames to a minimum of ETH_FRAME_LEN + FCS
> > (1518 bytes) everything starts working fine.
> That is quite unprecedented, either the switch is very bogus or there is
> something else we do not fully understand...

It would also be interesting to know if the frames on the wire have
the padding removed when needed. Its not going to be good for
performance if a TCP ACK is 1500bytes in size, rather than the usual

Have problems also been noticed with traffic going from user port to
user port?


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