From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pascal Hambourg Subject: Re: Forced lladdr change with bridge - or not? Date: Sun, 22 Aug 2010 22:53:04 +0200 Message-ID: <4C718E30.1090908@plouf.fr.eu.org> References: <4C715667.9070008@pandora.be> Mime-Version: 1.0 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: netfilter-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="iso-8859-1" To: Jan Engelhardt Cc: Bart De Schuymer , netfilter@vger.kernel.org Hello, Jan Engelhardt a =E9crit : > On Sunday 2010-08-22 18:55, Bart De Schuymer wrote: >>> # brctl addbr br0 >>> # brctl addif br0 tap1 >>> # brctl addif br0 tap2 >>> # ip a >>> 196: tap1: mtu 1500 qdisc noop state DOWN qle= n 500 >>> link/ether 9a:17:c4:65:e9:76 brd ff:ff:ff:ff:ff:ff >>> 197: tap2: mtu 1500 qdisc noop state DOWN qle= n 500 >>> link/ether ce:61:28:5a:b7:93 brd ff:ff:ff:ff:ff:ff >>> 198: br0: mtu 1500 qdisc noop state DOWN = link/ether >>> 9a:17:c4:65:e9:76 brd ff:ff:ff:ff:ff:ff >>> >>> Is this behavior normal that the lladdrs of all but the first brpor= t >>> remain unchanged? If so, what is the purpose of changing the lladdr= on the >>> first brport? >>> =20 >> I don't understand your question, Me neither : according to your output, the MAC address of neither port has changed. > but the Linux bridge code assigns the MAC >> address of its first-added port to the virtual bridge device. >=20 > 1. Why does it do that, The bridge interface must have a MAC address, so why not pick up one in thoses of its ports ? > 2. Why only the first port? IME, the bridge picks up the lowest MAC address of its ports. This has an advantage : the bridge MAC address ends up the same for a same set of ports regardless of the order in which the ports are added. But this also has a big disadvantage : the bridge MAC address can chang= e whenever you add or remove a port, breaking ARP for a while, changing link-local and stateless autoconfigured IPv6 addresses...