From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D87F1C3A59E for ; Mon, 26 Aug 2019 08:09:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AEB8E206BA for ; Mon, 26 Aug 2019 08:09:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730324AbfHZIJZ (ORCPT ); Mon, 26 Aug 2019 04:09:25 -0400 Received: from a3.inai.de ([88.198.85.195]:35764 "EHLO a3.inai.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728168AbfHZIJZ (ORCPT ); Mon, 26 Aug 2019 04:09:25 -0400 X-Greylist: delayed 590 seconds by postgrey-1.27 at vger.kernel.org; Mon, 26 Aug 2019 04:09:24 EDT Received: by a3.inai.de (Postfix, from userid 25121) id 80EC73BB696A; Mon, 26 Aug 2019 09:59:33 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by a3.inai.de (Postfix) with ESMTP id 7FE983BB6EEC; Mon, 26 Aug 2019 09:59:33 +0200 (CEST) Date: Mon, 26 Aug 2019 09:59:33 +0200 (CEST) From: Jan Engelhardt To: Florian Westphal cc: Rundong Ge , davem@davemloft.net, kuznet@ms2.inr.ac.ru, yoshfuji@linux-ipv6.org, netdev@vger.kernel.org, pablo@netfilter.org, kadlec@netfilter.org, roopa@cumulusnetworks.com, netfilter-devel@vger.kernel.org, coreteam@netfilter.org, bridge@lists.linux-foundation.org, nikolay@cumulusnetworks.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] bridge:fragmented packets dropped by bridge In-Reply-To: <20190730123542.zrsrfvcy7t2n3d4g@breakpoint.cc> Message-ID: References: <20190730122534.30687-1-rdong.ge@gmail.com> <20190730123542.zrsrfvcy7t2n3d4g@breakpoint.cc> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday 2019-07-30 14:35, Florian Westphal wrote: >Rundong Ge wrote: >> Given following setup: >> -modprobe br_netfilter >> -echo '1' > /proc/sys/net/bridge/bridge-nf-call-iptables >> -brctl addbr br0 >> -brctl addif br0 enp2s0 >> -brctl addif br0 enp3s0 >> -brctl addif br0 enp6s0 >> -ifconfig enp2s0 mtu 1300 >> -ifconfig enp3s0 mtu 1500 >> -ifconfig enp6s0 mtu 1500 >> -ifconfig br0 up >> >> multi-port >> mtu1500 - mtu1500|bridge|1500 - mtu1500 >> A | B >> mtu1300 > >How can a bridge forward a frame from A/B to mtu1300? There might be a misunderstanding here judging from the shortness of this thread. I understood it such that the bridge ports (eth0,eth1) have MTU 1500, yet br0 (in essence the third bridge port if you so wish) itself has MTU 1300. Therefore, frame forwarding from eth0 to eth1 should succeed, since the 1300-byte MTU is only relevant if the bridge decides the packet needs to be locally delivered.