netdev - Re: Distributed Switch Architecture(DSA)

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Message-ID: <20100619185739.GQ14513@mail.wantstofly.org>
Date:	Sat, 19 Jun 2010 20:57:39 +0200
From:	Lennert Buytenhek <buytenh@...tstofly.org>
To:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
Cc:	netdev@...r.kernel.org
Subject: Re: Distributed Switch Architecture(DSA)

On Sat, Jun 19, 2010 at 08:48:31PM +0200, Joakim Tjernlund wrote:

> > > > > Not sure how one would express whether VLAN tags should be stripped
> > > > > off or not when egressing the HW switch's physical port.
> > > >
> > > > If you transmit a packet onto 'lan', it will be sent to the switch chip
> > > > with an "untagged" DSA tag.  If you transmit a packet onto 'lan.123',
> > > > it will be sent to the switch chip with a "tagged" DSA tag.  See
> > > > net/dsa/tag_dsa.c for details.
> > >
> > > Ah, now I get it, thanks.
> > > However, how does this work for LAN to LAN pkgs? LAN1 and LAN2 could be
> > > in the same VLAN but one is implicit(port) VLAN and the
> > > other is explicit.
> >
> > If you tell the HW switch to forward these packets, they will never
> > appear at the CPU interface, so the DSA tagging/untagging doesn't enter
> > the picture.
> 
> "tell the HW switch"? Doesn't DSA do that already?

Not in its current iteration, as I've explained in previous emails.


> If not, what is the point of DSA then if it doesn't use the native
> forwarding capabilities of the HW switch?

The point is and always was to provide a framework for proper integration
of hardware switch chips into the Linux kernel.  This framework doesn't
become useless just because it doesn't already support every single
hardware feature at this point.


> > > How do I config the HW switch to do that?
> >
> > Tell the switch that the vlan is native on one of the ports but not on
> > the other.  It's been a while since I looked at the chip docs but there
> > are ways of doing this.
> 
> The current DSA impl. does not support this? There should be some
> way to manage this within the DSA framework.

Have you even tried the DSA code?
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