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=-4.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 20D79C4320A for ; Mon, 2 Aug 2021 13:37:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 07A9F60FA0 for ; Mon, 2 Aug 2021 13:37:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233978AbhHBNhX (ORCPT ); Mon, 2 Aug 2021 09:37:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35678 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233764AbhHBNhW (ORCPT ); Mon, 2 Aug 2021 09:37:22 -0400 Received: from mail-oi1-x22f.google.com (mail-oi1-x22f.google.com [IPv6:2607:f8b0:4864:20::22f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5B57DC06175F; Mon, 2 Aug 2021 06:37:12 -0700 (PDT) Received: by mail-oi1-x22f.google.com with SMTP id u10so24087443oiw.4; Mon, 02 Aug 2021 06:37:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=PbcBzYCDzjM/TKXUy4gd/mf09bcYCldaAFLfvfQnHzQ=; b=DwaAWEc4Q6Uca77i1pa2FzsHjwr9/FjCJvqewvhgiKAby+uKugn8R/1vtl381tQ9TD zD6mjWM7EDPmBy87dl6240otKOcRKK1tPlXJY1ZXkmxjjFZBhIk06BhMdPmByoKvaPqg Y3mtrBAYzvH3br9rxFH3OmFeiQ//k8GQ/IFamrv3tamOfxhY+RJQzGqYHx+AToApOs17 mwY54HJmk5kv5ObixIBouxDiRRWFFhhXyumRy56FpmsZ18OAF6ob0pvtdJsHllSVets1 NRS7JS7nUCA04dXRUjgz0WM4Mcm0r3xQY8IQnLSI9OoH+2FoLlk6ZZDuNurkvBpCGMUJ l9CQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=PbcBzYCDzjM/TKXUy4gd/mf09bcYCldaAFLfvfQnHzQ=; b=cluepT3ZAVK36QsmYZSw8tfPvOqohrQjlhJ4DSM0MQCB50zFMoXp7ButbY8Oup0cVo o5jhOLvgxQty2leYBHYg+oCfhHtEsZ8cNxPHCDUMftyeGy+z91vYM11MxCE5pOHJa/UI V4j1eeKjT+LeKlzzoYI7UPikAzNvUkXRAtkXoDEpa4iw+lTwnkzTenYOZNGdlfMK2b5o tv3heu7Ed0sG/Ab4AbJPzgHLQeubMMwGZX04TVKdDgsjGn4lnGsJRJtBZkBQkTq8JTXl PTsOrUttY+TDUU9T0IIqAKfdEGhGEaSUUI2HzmXDP+tM6SlqfFHDnbkapRsfz9lAUqve BMIw== X-Gm-Message-State: AOAM530eCHU8USaE3x9YUUjPXzQx5IHClHGNsdtkmU8CdjXTJJin0EcU 2aeTB7vI0HBbmR38YKJCqns= X-Google-Smtp-Source: ABdhPJyf6PwIBiYKEvn/j5AUOIaUsrJFqOISQa5mzqZHiymrzID1xoPdYD1lL+ot9DwqGtiWx7VCEQ== X-Received: by 2002:a05:6808:13c5:: with SMTP id d5mr10367796oiw.56.1627911431838; Mon, 02 Aug 2021 06:37:11 -0700 (PDT) Received: from Davids-MacBook-Pro.local ([8.48.134.27]) by smtp.googlemail.com with ESMTPSA id r5sm1856639oti.5.2021.08.02.06.37.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Aug 2021 06:37:11 -0700 (PDT) Subject: Re: [PATCH net-next v2] ipv6: add IFLA_INET6_RA_MTU to expose mtu value in the RA message To: Rocco Yue , David Ahern Cc: "David S . Miller" , Jakub Kicinski , Hideaki YOSHIFUJI , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, rocco.yue@gmail.com, chao.song@mediatek.com, zhuoliang.zhang@mediatek.com References: <5be90cf4-f603-c2f2-fd7e-3886854457ba@gmail.com> <20210802031924.3256-1-rocco.yue@mediatek.com> From: David Ahern Message-ID: Date: Mon, 2 Aug 2021 07:37:08 -0600 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20210802031924.3256-1-rocco.yue@mediatek.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/1/21 9:19 PM, Rocco Yue wrote: > On Sat, 2021-07-31 at 11:17 -0600, David Ahern wrote: > On 7/30/21 7:52 PM, Rocco Yue wrote: >>> In this way, if the MTU values that the device receives from >>> the network in the PCO IPv4 and the RA IPv6 procedures are >>> different, the user space process can read ra_mtu to get >>> the mtu value carried in the RA message without worrying >>> about the issue of ipv4 being stuck due to the late arrival >>> of RA message. After comparing the value of ra_mtu and ipv4 >>> mtu, then the device can use the lower MTU value for both >>> IPv4 and IPv6. >> >> you are storing the value and sending to userspace but never using it >> when sending a message. What's the pointing of processing the MTU in the >> RA if you are not going to use it to control message size? > > Hi David, > > In the requirement of mobile operator at&t in 2021: > AT&T Prioritize Lower MTU value: > If the MTU values that the device receives from the network in the PCO > IPv4 and the RA IPv6 procedures are different, > then the device shall use the lower MTU value for both IPv4 and IPv6. > > And in the 3GPP 23.060: > The PDP PDUs shall be routed and transferred between the MS and the GGSN > or P-GW as N-PDUs. In order to avoid IP layer fragmentation between the > MS and the GGSN or P-GW, the link MTU size in the MS should be set to the > value provided by the network as a part of the IP configuration. This > applies to both IPv6 and IPv4. > > That means user needs to be able to correctly read the mtu value carried > in the RA message so that user can correctly compare PCO ipv4 mtu and > RA ipv6 mtu. > Then userspace should get a link notification when ra_mtu is set so it does not have to poll.