netdev - Re: [PATCH v3 net 2/9] bridge: Fix the way to insert new local fdb entries in br_fdb

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Date:	Sat, 08 Feb 2014 11:43:48 +0900
From:	Toshiaki Makita <toshiaki.makita1@...il.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
	"David S . Miller" <davem@...emloft.net>,
	Vlad Yasevich <vyasevic@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v3 net 2/9] bridge: Fix the way to insert new local fdb
 entries in br_fdb_changeaddr

On Fri, 2014-02-07 at 09:31 -0700, Stephen Hemminger wrote:
> On Fri,  7 Feb 2014 16:48:19 +0900
> Toshiaki Makita <makita.toshiaki@....ntt.co.jp> wrote:
> 
> > Since commit bc9a25d21ef8 ("bridge: Add vlan support for local fdb entries"),
> > br_fdb_changeaddr() has inserted a new local fdb entry only if it can
> > find old one. But if we have two ports where they have the same address
> > or user has deleted a local entry, there will be no entry for one of the
> > ports.
> > 
> > Example of problematic case:
> >   ip link set eth0 address aa:bb:cc:dd:ee:ff
> >   ip link set eth1 address aa:bb:cc:dd:ee:ff
> >   brctl addif br0 eth0
> >   brctl addif br0 eth1 # eth1 will not have a local entry due to dup.
> 
> I think the second addif should fail, it doesn't seem valid to have
> two interfaces on same bridge with same address. Most hardware switches
> would disable the port in that case.

Thank you for your comment, but I don't think so for several reasons.

- From other network elements on the same network, bridge ports don't
appear to have a mac address, but the bridge appears to have several mac
addresses that can reach to the bridge. The duplicated address is simply
seen as one of those addresses. I don't think it is a problem.

- This operation (add a port that has duplicated address) has allowed
for several years, and it is obviously intended, as commented in
fdb_insert().

417                 /* it is okay to have multiple ports with same
418                  * address, just use the first one.
419                  */

- Hardware switches usually have one mac address per one switch. Their
ports don't have mac addresses. It is not reasonable to compare hardware
switches.

Thanks,
Toshiaki Makita

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