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 904F8C433E1 for ; Sun, 12 Jul 2020 22:39:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 65AF620663 for ; Sun, 12 Jul 2020 22:39:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="VVM3P9nI" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728140AbgGLWjs (ORCPT ); Sun, 12 Jul 2020 18:39:48 -0400 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:32362 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727795AbgGLWjs (ORCPT ); Sun, 12 Jul 2020 18:39:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1594593587; 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=LFfzGviOYxW9rceC8tkrnK7xNZwZvK4+TkMyAjQ4oe0=; b=VVM3P9nILTX7SI46lvsO2OuquVHaF01LxX/wFr38YXJeDMqxVuvLKZ+qvtDIC1RRBxooJT 4UE2X8ermhAl6lNW5gL9DIW/KUjNQWgd7uKt7jAfc0YTdKUXzCkuz02gCyXN4ErGemYCcf d79M4Rjkm2SY7HAP8IoDm73MnglHuc4= 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-34-Yr4dUYENPUCUTdUGJNsLJw-1; Sun, 12 Jul 2020 18:39:45 -0400 X-MC-Unique: Yr4dUYENPUCUTdUGJNsLJw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 304F6106B242; Sun, 12 Jul 2020 22:39:44 +0000 (UTC) Received: from elisabeth (unknown [10.36.110.62]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E0386724D1; Sun, 12 Jul 2020 22:39:41 +0000 (UTC) Date: Mon, 13 Jul 2020 00:39:33 +0200 From: Stefano Brivio To: Florian Westphal Cc: , aconole@redhat.com Subject: Re: [PATCH net-next 0/3] vxlan, geneve: allow to turn off PMTU updates on encap socket Message-ID: <20200713003933.292755b4@elisabeth> In-Reply-To: <20200712200705.9796-1-fw@strlen.de> References: <20200712200705.9796-1-fw@strlen.de> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Sun, 12 Jul 2020 22:07:02 +0200 Florian Westphal wrote: > There are existing deployments where a vxlan or geneve interface is part > of a bridge. > > In this case, MTU may look like this: > > bridge mtu: 1450 > vxlan (bridge port) mtu: 1450 > other bridge ports: 1450 > > physical link (used by vxlan) mtu: 1500. > > This makes sure that vxlan overhead (50 bytes) doesn't bring packets over the > 1500 MTU of the physical link. > > Unfortunately, in some cases, PMTU updates on the encap socket > can bring such setups into a non-working state: no traffic will pass > over the vxlan port (physical link) anymore. > Because of the bridge-based usage of the vxlan interface, the original > sender never learns of the change in path mtu and TCP clients will retransmit > the over-sized packets until timeout. > > > When this happens, a 'ip route flush cache' in the netns holding > the vxlan interface resolves the problem, i.e. the network is capable > of transporting the packets and the PMTU update is bogus. > > Another workaround is to enable 'net.ipv4.tcp_mtu_probing'. > > This patch series allows to configure vxlan and geneve interfaces > to ignore path mtu updates. Regardless of the comments to 1/3, I don't have any problem with this (didn't review yet) if it's the only way to currently work around the issue (of course :)). I think we should eventually fix PMTU discovery for bridged setups, but perhaps it's more complicated than that. I wonder, though: - wouldn't setting /proc/sys/net/ipv4/ip_no_pmtu_disc have the same effect? - does it really make sense to have this configurable for IPv6? -- Stefano