From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Lunn Subject: Should the bridge learn from frames with link local destination MAC address? Date: Fri, 9 Nov 2018 04:24:43 +0100 Message-ID: <20181109032443.GA23331@lunn.ch> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev , Florian Fainelli To: Roopa Prabhu , Nikolay Aleksandrov Return-path: Received: from vps0.lunn.ch ([185.16.172.187]:56205 "EHLO vps0.lunn.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727311AbeKINDX (ORCPT ); Fri, 9 Nov 2018 08:03:23 -0500 Content-Disposition: inline Sender: netdev-owner@vger.kernel.org List-ID: Hi Roopa, Nikolay br_handle_frame() looks out for frames with a destination MAC addresses with is Ethernet link local, those which fit 01-80-C2-00-00-XX. It does not normally forward these, but it will deliver them locally. Should the bridge perform learning on such frames? I've got a setup with two bridges connected together with multiple links between them. STP has done its thing, and blocked one of the ports to solve the loop. host0 host1 +-----------------+ +-----------------+ | lan0 forwarding |-----| lan0 forwarding | | | | | | lan1 forwarding |-----| lan1 blocked | +-----------------+ +-----------------+ I have LLDP running on both system, and they are sending out periodic frames on each port. Now, lan0 and lan1 on host1 use the same MAC address. So i see the MAC address bouncing between ports because of the LLDP packets. # bridge monitor 00:26:55:d2:27:a8 dev lan1 master br0 00:26:55:d2:27:a8 dev lan0 master br0 00:26:55:d2:27:a8 dev lan1 master br0 00:26:55:d2:27:a8 dev lan0 master br0 00:26:55:d2:27:a8 dev lan1 master br0 This then results in normal traffic from host0 to host1 being sent to the blocked port for some of the time. LLDP is using 01-80-C2-00-00-0E, a link local MAC address. If the bridge did not learn on such frames, i think this setup would work. The bridge would learn from ARP, IP etc, coming from the forwarding port of host1, and the blocked port would be ignored. I've tried a similar setup with a hardware switch, Marvell 6352. It never seems to learn from such frames. Thanks Andrew