linux-kernel - Re: [PATCH net-next 7/9] net: dsa: mv88e6xxx: restore VLANTable map control

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Message-ID: <20160226223516.GC1560@lunn.ch>
Date:	Fri, 26 Feb 2016 23:35:16 +0100
From:	Andrew Lunn <andrew@...n.ch>
To:	Kevin Smith <kevin.smith@...csyscorp.com>
Cc:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kernel@...oirfairelinux.com" <kernel@...oirfairelinux.com>,
	"David S. Miller" <davem@...emloft.net>,
	Florian Fainelli <f.fainelli@...il.com>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Neil Armstrong <narmstrong@...libre.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Russell King <rmk+kernel@....linux.org.uk>
Subject: Re: [PATCH net-next 7/9] net: dsa: mv88e6xxx: restore VLANTable map
 control

On Fri, Feb 26, 2016 at 10:12:28PM +0000, Kevin Smith wrote:
> Hi Vivien, Andrew,
> 
> On 02/26/2016 03:37 PM, Vivien Didelot wrote:
> > Here, 5 is the CPU port and 6 is a DSA port.
> >
> > After joining ports 0, 1, 2 in the same bridge, we end up with:
> >
> > Port  0  1  2  3  4  5  6
> >    0   -  *  *  -  -  *  *
> >    1   *  -  *  -  -  *  *
> >    2   *  *  -  -  -  *  *
> >    3   -  -  -  -  -  *  *
> >    4   -  -  -  -  -  *  *
> >    5   *  *  *  *  *  -  *
> >    6   *  *  *  *  *  *  -
> The case I am concerned about is if the switch connected over DSA in 
> this example has a WAN port on it, which can legitimately route to the 
> CPU on port 5 but should not route to the LAN ports 0, 1, and 2.  Does 
> this VLAN allow direct communication between the WAN and LAN?  Or is 
> this prevented by DSA or some other mechanism?

A typical WIFI access point with a connection to a cable modem.

So in linux you have interfaces like

lan0, lan1, lan2, lan3, wan0

DSA provides you these interface. And by default they are all
separated. There is no path between them. You can consider them as
being separate physical ethernet cards, just like all other interfaces
in linux.

What you would typically do is:

brctl addbr br0
brctl addif br0 lan0
brctl addif br0 lan1
brctl addif br0 lan2
brctl addif br0 lan3

to create a bridge between the lan ports. The linux kernel will then
push this bridge configuration down into the hardware, so the switch
can forward frames between these ports.

The wan port is not part of the bridge, so there is no L2 path to the
WAN port. You need to do IP routing on the CPU.

Linux takes the stance that switch ports interfaces should act just
like any other linux interface and you configure them in the normal
linux way.

    Andrew