netdev - Re: [Query]: DSA Understanding

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Date:   Mon, 13 Aug 2018 16:58:53 +0100
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [Query]: DSA Understanding

Hi Andrew/Florain,

On Mon, Aug 13, 2018 at 2:38 PM Andrew Lunn <andrew@...n.ch> wrote:
>
> > > I agree, this should be padding packets correctly, can you still
> > > instrument cpsw to make sure that what comes to its ndo_start_xmit() is
> > > ETH_ZLEN + tag_len or more?
> > >
> > Yes I can confirm the skb->len is always >= 62 (ETH_ZLEN + 2)
>
> Which switch are you using?
>
> Marvell switches use either 4 or 8 bytes of tag. Broadcom has 4, KSZ
> has 1 for packets going to the switch, lan9303 has 4, mtd uses 4, qca
> has 2.
>
I am using the KSZ switch. for Ingress it has 1 byte and for Egress it
has 2 bytes.
I came across patch [1] and padded 2 more bytes in ksz_xmit() and I was
successfully able to ping from lan4 to PC. Thank you very much for
your guidance/support.

Now I have stumbled into a different issue:

Case 1 Works:
=================
lan0 = 192.168.0.1
PC1 = 192.168.0.10
For the above ping works from both directions.

CASE 2 Doesn’t Work:
=========================
lan0 = 192.168.0.1
PC1 = 192.168.0.10
lan4 = 192.168.0.4
PC2 = 192.168.0.11

Ping from lan0 to PC1 and PC1 to lan0 works
But ping from PC2 to lan4 and lan4 to PC2 fails.

CASE 3 Works:
=========================
lan0 = 192.168.0.1
PC1 = 192.168.0.10
lan4 = 192.168.4.4
PC2 = 192.168.4.11

With the above setup ping works.

[Query] Why does ping fail in case 2. Any thoughts what I am missing here ?
or is it the expected behaviour ?

[1] https://lore.kernel.org/patchwork/patch/851457/

Cheers,
--Prabhakar Lad