netdev - Re: [Query]: DSA Understanding

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Message-ID: <20180809120159.GA16359@lunn.ch>
Date:   Thu, 9 Aug 2018 14:01:59 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: [Query]: DSA Understanding

On Thu, Aug 09, 2018 at 12:31:31PM +0100, Lad, Prabhakar wrote:
> Hi Andrew,
> 
> On Thu, Aug 2, 2018 at 5:05 PM Andrew Lunn <andrew@...n.ch> 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?
> >
> I dont see any drops/errors on the PC, following is the dump from PC:
> 
> sudo ethtool -S enx00e04c68c229
> [sudo] password for prabhakar:
> NIC statistics:
>      tx_packets: 1659
>      rx_packets: 485
>      tx_errors: 0
>      rx_errors: 0
>      rx_missed: 0
>      align_errors: 0
>      tx_single_collisions: 0
>      tx_multi_collisions: 0
>      rx_unicast: 18
>      rx_broadcast: 295
>      rx_multicast: 172
>      tx_aborted: 0
>      tx_underrun: 0

So there are received packets at the PC. Not many unicast, mostly
broadcast, which fits with ARP. What does wireshark tell you about
these received packets? Are they ARP replies? Are they something else?
If they are ARP replies, why are they being ignored?  I don't know if
tshark will show you CRC problems. Wireshark does, when you unfold a
packet, and look at the fields in detail.

> Seems like the packet is not being transmitted from the switch at all
> ? (as ping from switch lan4 to PC fails)

I don't think you can make that conclusion yet. The PC is receiving
something, rx_packets=485. What are those packets?

Look at the statistics along the chain, from the target to the PC.
Look at the master device, lan4 and the PC. You should see about one
packet per second transmitted on the master device. One packet per
second transmitted on lan4, and one packet per second received on the
PC. Where does this break down.

	   Andrew