netdev - Re: [Query]: DSA Understanding

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Message-ID: <20180809120802.GB16359@lunn.ch>
Date:   Thu, 9 Aug 2018 14:08:02 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [Query]: DSA Understanding

On Thu, Aug 09, 2018 at 12:33:30PM +0100, Lad, Prabhakar wrote:
> Hi Florain,
> 
> Thanks for your reply.
> 
> On Thu, Aug 2, 2018 at 5:24 PM Florian Fainelli <f.fainelli@...il.com> wrote:
> >
> >
> >
> > On 08/02/2018 09:05 AM, Andrew Lunn wrote:
> > >> I dont see any Reply's on the PC with tcpdump on PC
> > >
> > > So try ethool -S on the PC. Any packets dropped because of errors?
> > >
> > > Try turning off hardware checksums on the switch. ethtool -K.
> >
> > Also make sure that cpsw is properly sending 64 bytes (including FCS)
> > packets to the switch, some switches will just discard packets when
> > packets are RUNT
> 
> how can I dump the FCS from the switch (can I use tshark ?)

tskark running on the target will not show you the FCS. The Ethernet
hardware should calculate that as it sends the packet. Wireshark on
the PC might, but some Ethernet cards strip off the FCS before passing
it to the stack.

What is important here is the idea of a runt packet. You appear to be
receiving some packets at the PC, if we can trust the statistics you
showed. Are those received packets all big? Are the small ARP replies
missing?

	Andrew