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=-5.5 required=3.0 tests=BAYES_00, 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 38E96C433E1 for ; Wed, 15 Jul 2020 12:43:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1F86120578 for ; Wed, 15 Jul 2020 12:43:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729198AbgGOMnB (ORCPT ); Wed, 15 Jul 2020 08:43:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34876 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726335AbgGOMnA (ORCPT ); Wed, 15 Jul 2020 08:43:00 -0400 Received: from Chamillionaire.breakpoint.cc (Chamillionaire.breakpoint.cc [IPv6:2a0a:51c0:0:12e:520::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A37C5C061755 for ; Wed, 15 Jul 2020 05:43:00 -0700 (PDT) Received: from fw by Chamillionaire.breakpoint.cc with local (Exim 4.92) (envelope-from ) id 1jvgkU-0001R5-TJ; Wed, 15 Jul 2020 14:42:58 +0200 Date: Wed, 15 Jul 2020 14:42:58 +0200 From: Florian Westphal To: Stefano Brivio Cc: Florian Westphal , David Ahern , netdev@vger.kernel.org, aconole@redhat.com Subject: Re: [PATCH net-next 1/3] udp_tunnel: allow to turn off path mtu discovery on encap sockets Message-ID: <20200715124258.GP32005@breakpoint.cc> References: <20200712200705.9796-1-fw@strlen.de> <20200712200705.9796-2-fw@strlen.de> <20200713003813.01f2d5d3@elisabeth> <20200713080413.GL32005@breakpoint.cc> <20200713140219.GM32005@breakpoint.cc> <20200714143327.2d5b8581@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200714143327.2d5b8581@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Stefano Brivio wrote: > I would still like the idea I proposed better (updating MTUs down the > chain), it's simpler and we don't have to duplicate existing > functionality (generating additional ICMP messages). It doesn't make this work though. With your skeleton patch, br0 updates MTU, but the sender still won't know that unless input traffic to br0 is routed (or locally generated). Furthermore, such MTU reduction would require a mechanism to auto-reconfig every device in the same linklevel broadcast domain, and I am not aware of any such mechanism.