netdev - Re: [Query]: DSA Understanding

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Message-ID: <CA+V-a8vAuigs9GTUa7AwRY8YR6ti9N90-RsChoDdRPxYMGWoWg@mail.gmail.com>
Date:   Thu, 9 Aug 2018 13:45:52 +0100
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: [Query]: DSA Understanding

On Thu, Aug 9, 2018 at 1:02 PM Andrew Lunn <andrew@...n.ch> wrote:
>
> 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?
>
The received packets captured on the PC are MDNS and DHPC, these MDNS
are causing the rx
packet counter go up:

685    682.956266963    0.0.0.0    255.255.255.255    DHCP    422
DHCP Discover - Transaction ID 0x9d832fac
550    555.543322200    0.0.0.0    255.255.255.255    DHCP    422
DHCP Discover - Transaction ID 0x9d832fac
572    576.738682378    fe80::2f12:3d45:7cca:57fa    ff02::fb    MDNS
  136    Standard query 0x0000 AAAA VB4-SN00000000.local, "QM"
question SRV VB4-SN00000000._sftp-ssh._tcp.local, "QM" question
630    630.706578680    169.254.126.126    224.0.0.251    MDNS    168
  Standard query response 0x0000 AAAA, cache flush
fe80::c6f3:12ff:fe08:fe7f SRV, cache flush 0 0 22 VB4-SN00000000.local
A, cache flush 169.254.126.126
732    728.982449369    169.254.78.251    224.0.0.251    MDNS    122
 Standard query 0x0000 AAAA VB4-SN00000000.local, "QM" question A
VB4-SN00000000.local, "QM" question SRV
VB4-SN00000000._sftp-ssh._tcp.local, "QM" question
733    728.983534948    169.254.126.126    224.0.0.251    MDNS    168
  Standard query response 0x0000 SRV, cache flush 0 0 22
VB4-SN00000000.local AAAA, cache flush fe80::c6f3:12ff:fe08:fe7f A,
cache flush 169.254.126.126

> 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.
>
I don’t see any packets reaching the PC for the ping request. I can see the
RX and TX on the switch for lan4 increasing every second. seems like the
switch itself is consuming it and not forwarding(but then lan4 TX
shouldn’t have incremented ?).

any thoughts where I could focusing on the switch or cpsw ?

Cheers,
--Prabhakar Lad