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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 1334DC433E3 for ; Sat, 18 Jul 2020 17:59:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E538820717 for ; Sat, 18 Jul 2020 17:59:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Z+uuqjC4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728106AbgGRR7E (ORCPT ); Sat, 18 Jul 2020 13:59:04 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:36387 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728088AbgGRR7D (ORCPT ); Sat, 18 Jul 2020 13:59:03 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1595095142; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=YOC3JVzPDRJhj3DObWDI+eRxn6AScgc2CNNC0ur8YY8=; b=Z+uuqjC436f7nIqAj6snvN2gdpFoH9CWsMzCXM2SAcfrmCmFxg1qbW5Tlp64YR13uxdfXN FOh4AfIDjIXF99bV9ZNMw8jWKUlY6Bpax9crzyYN1Dox6BjA2uZLDHskfGHWFViU5lGpXn zEosDEWV1HpMVlV7rGfIQYLeP12TZQM= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-194-AErGAKYCPzqPt3p_G0o39A-1; Sat, 18 Jul 2020 13:58:58 -0400 X-MC-Unique: AErGAKYCPzqPt3p_G0o39A-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F3D0A1081; Sat, 18 Jul 2020 17:58:56 +0000 (UTC) Received: from elisabeth (unknown [10.36.110.8]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8D33C10013C4; Sat, 18 Jul 2020 17:58:55 +0000 (UTC) Date: Sat, 18 Jul 2020 19:58:50 +0200 From: Stefano Brivio To: David Ahern Cc: Florian Westphal , 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: <20200718195850.61104dd2@elisabeth> In-Reply-To: <9e47f521-b3dc-f116-658b-d6897b0ddf20@gmail.com> 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> <20200715124258.GP32005@breakpoint.cc> <20200715153547.77dbaf82@elisabeth> <20200715143356.GQ32005@breakpoint.cc> <20200717142743.6d05d3ae@elisabeth> <89e5ec7b-845f-ab23-5043-73e797a29a14@gmail.com> <20200718085645.7420da02@elisabeth> <9e47f521-b3dc-f116-658b-d6897b0ddf20@gmail.com> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Sat, 18 Jul 2020 11:02:46 -0600 David Ahern wrote: > On 7/18/20 12:56 AM, Stefano Brivio wrote: > > On Fri, 17 Jul 2020 09:04:51 -0600 > > David Ahern wrote: > > > >> On 7/17/20 6:27 AM, Stefano Brivio wrote: > >>>> > >>>>> Note that this doesn't work as it is because of a number of reasons > >>>>> (skb doesn't have a dst, pkt_type is not PACKET_HOST), and perhaps we > >>>>> shouldn't be using icmp_send(), but at a glance that looks simpler. > >>>> > >>>> Yes, it also requires that the bridge has IP connectivity > >>>> to reach the inner ip, which might not be the case. > >>> > >>> If the VXLAN endpoint is a port of the bridge, that needs to be the > >>> case, right? Otherwise the VXLAN endpoint can't be reached. > >>> > >>>>> Another slight preference I have towards this idea is that the only > >>>>> known way we can break PMTU discovery right now is by using a bridge, > >>>>> so fixing the problem there looks more future-proof than addressing any > >>>>> kind of tunnel with this problem. I think FoU and GUE would hit the > >>>>> same problem, I don't know about IP tunnels, sticking that selftest > >>>>> snippet to whatever other test in pmtu.sh should tell. > >>>> > >>>> Every type of bridge port that needs to add additional header on egress > >>>> has this problem in the bridge scenario once the peer of the IP tunnel > >>>> signals a PMTU event. > >>> > >>> Yes :( > >> > >> The vxlan/tunnel device knows it is a bridge port, and it knows it is > >> going to push a udp and ip{v6} header. So why not use that information > >> in setting / updating the MTU? That's what I was getting at on Monday > >> with my comment about lwtunnel_headroom equivalent. > > > > If I understand correctly, you're proposing something similar to my > > earlier draft from: > > > > <20200713003813.01f2d5d3@elisabeth> > > https://lore.kernel.org/netdev/20200713003813.01f2d5d3@elisabeth/ > > > > the problem with it is that it wouldn't help: the MTU is already set to > > the right value for both port and bridge in the case Florian originally > > reported. > > I am definitely hand waving; I have not had time to create a setup > showing the problem. Is there a reproducer using only namespaces? And I'm laser pointing: check the bottom of that email ;) -- Stefano