netdev - Re: [PATCH] bridge: mask forwarding of IEEE 802 local multicast groups

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Date:	Tue, 12 Jul 2011 13:36:43 +0200
From:	David Lamparter <equinox@...c24.net>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
Cc:	Nick Carter <ncarter100@...il.com>, netdev@...r.kernel.org,
	Michał Mirosław <mirqus@...il.com>,
	David Lamparter <equinox@...c24.net>, davem@...emloft.net
Subject: Re: [PATCH] bridge: mask forwarding of IEEE 802 local multicast
 groups

On Mon, Jul 11, 2011 at 08:27:55AM -0700, Stephen Hemminger wrote:
> On Sun, 10 Jul 2011 17:04:30 +0100
> Nick Carter <ncarter100@...il.com> wrote:
> 
> > Updated diffs so they apply to net-next (Original diffs were based off 2.6.38).
> > 
> > Any chance of getting these diffs applied?  The default behaviour of
> > the bridge code is unchanged.  They solve the problem of
> > authenticating a virtual 802.1x supplicant machine against an external
> > 802.1X authenticator.  It is also a general solution that allows the
> > forwarding of any combination of the IEEE 802 local multicast groups.
> > 
> > Signed-off-by: Nick Carter <ncarter100@...il.com>
> > Reviewed-by: David Lamparter <equinox@...c24.net>
> 
> I am still undecided on this. Understand the need, but don't like idea
> of bridge behaving in non-conforming manner. Will see if IEEE 802 committee
> has any input.

The patch doesn't make the bridge behave nonconformant. The default mask
is 0, which just keeps the old behaviour.

If you set the lowest 3 bits, yes, you can break your network. But so
does enabling proxy_arp in most cases. And there are reasonable use
cases for it, both 802.1X forwarding and fully-transparent* packet
capture bridges benefit from it. And the latter is something I wouldn't
wish to move to userspace either.

Maybe we should add a warning if the lowest 3 bits are set, like
"you have enabled forwarding of STP/Pause/Bond frames. This can
thoroughly break your network."

* excl. pause frames, sadly - those get eaten by hw/driver...

> Also, don't want to build more knobs in with sysfs that are per-bridge.
> Eventually, the plan is to make all the setting per-port with sysctl's
> like IPv6.

This setting doesn't make sense per-port IMHO. Also, sysctl?!

-David

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