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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-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210802_063712_721254_D942C942 X-CRM114-Status: GOOD ( 23.50 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel