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Mon, 30 Nov 2020 22:50:35 +0000 Subject: Re: warnings from MTU setting on switch ports To: Vladimir Oltean Cc: Network Development , Florian Fainelli , Andrew Lunn References: <20201130160439.a7kxzaptt5m3jfyn@skbuf> <61a2e853-9d81-8c1a-80f0-200f5d8dc650@prevas.dk> <20201130223507.rav22imba73dtfxb@skbuf> From: Rasmus Villemoes Message-ID: <2d4024ef-f80a-475f-a247-e02971b55152@prevas.dk> Date: Mon, 30 Nov 2020 23:50:34 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 In-Reply-To: <20201130223507.rav22imba73dtfxb@skbuf> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [5.186.115.188] X-ClientProxiedBy: AM6PR10CA0046.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:209:80::23) To AM0PR10MB1874.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:208:3f::10) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.1.149] (5.186.115.188) by AM6PR10CA0046.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:209:80::23) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3611.22 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: =?Windows-1252?Q?iVDdwkydrIgih4xQN5bMD3SJSSEpia/SBgp2JbRjcKJ6wRGqOy5K0Z4K?= =?Windows-1252?Q?WqOZXK1r3R5NTueDzCdb/GI0H0sqdW7CgUYZD2Cd4ViGuECV+gUcLgd1?= =?Windows-1252?Q?1/OPb9fk8ALWJDmEkFWhMP4oItk7cYGw91rIw42hu6tVRXeczNsbmkkD?= =?Windows-1252?Q?QNQpFzK3fsv4TsgTM5uTWap+RmF0faGCxN5dyKjzVCoaCode5gTAVkQw?= =?Windows-1252?Q?DW/XkAtulh6j2CmIfo1tPCLNp4AYhwXH/TkquvhRvxuThyOT1dA5WX3e?= =?Windows-1252?Q?YPQY15nrKo4bRuNEIIl67SLOvaitDqhnDAACshLwOaf8fj2b5U5ZypBn?= =?Windows-1252?Q?3ZllnR7KQy+oZXQ5diI/OvfCoLZ6JMY5WrvpGCRn5pmrK5EmS6OmRbRg?= =?Windows-1252?Q?7i56Zx4lotE0AOPMx+ZNO6Yo7DBOloDgSai6Dj7JYbAR74agIdAIUL6Y?= =?Windows-1252?Q?37TJBpPBV+JfJXoYgQ0rlBN5Bkl/MARebwZkZg4N6ObGX1Y0DidhIe0E?= =?Windows-1252?Q?8vn/imCGA2/p2A5uDY4syNfM33C8V6N1qtvLuKo8xbf6mjBUl4U8NfsZ?= =?Windows-1252?Q?rlAzC636i0UVfTE0PoH0fc/LeLVvl5zTRh57PrD6FrLbIZ24ssUrFjo8?= =?Windows-1252?Q?g8+pAILqZ8rzFrTmv0N7tPDJo/g5QjEtim1zZo7U5N3xzFdKq3BJkA16?= =?Windows-1252?Q?edsWD+M+spEeegYOoblK0n2nnLJKkurRC4kSXFGqn4n9oZ+t7qbpZzcz?= =?Windows-1252?Q?WoZ/XS7ChU3kFjz0tUD3eIXHEKFQ3KloVaWs2vENpnnKArlLFcLGLAzp?= =?Windows-1252?Q?GQwi0v7B5+4ZJGa6j4V27uZ4rD4Y/AmLnmsOuLAuh6HRCmOlKDbqayvT?= =?Windows-1252?Q?JmofGwylirfRSkUcgUz9SNoSJ4StTYof9DSIrOj2OnFUZw44sAq8KQRp?= =?Windows-1252?Q?OexGG3h/g2Vm5FAP2fBGdX7msyIrRRInUbyEUvB61sDIGDVca7WU8KSk?= =?Windows-1252?Q?c0iRMiyNU/0qiq6KUdpcjwYfgZuLlc5WG7bMgrqtiah4hJrHMZniGioB?= =?Windows-1252?Q?CeCx1vYTeeNpekeu?= X-OriginatorOrg: prevas.dk X-MS-Exchange-CrossTenant-Network-Message-Id: 2badab8c-b253-4d76-ff9f-08d8958259a7 X-MS-Exchange-CrossTenant-AuthSource: AM0PR10MB1874.EURPRD10.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Nov 2020 22:50:35.6333 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: d350cf71-778d-4780-88f5-071a4cb1ed61 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: tUOSQX/3PZkVUsAUYTM+qtsJ0ojZLCU9XQB+KlVoIZWQIiG4h6+y6GFA4WMBfIkhSmFW9S9pYP8i/Nc8dXnIGPUXbDcSYSwrDchF87qqAw4= X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM0PR10MB2356 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 30/11/2020 23.35, Vladimir Oltean wrote: > On Mon, Nov 30, 2020 at 11:13:39PM +0100, Rasmus Villemoes wrote: >> FWIW, on a 4.19 kernel, I can do 'ping -s X -M do' for X up to 1472 >> for IPv4 and 1452 for IPv6, but I don't think that tells me much about >> what the hardware could do. > > IP will get fragmented by the stack to the interface's MTU. Nope, that's what the '-M do' is for: # ping -M do -s 1880 169.254.246.13 PING 169.254.246.13 (169.254.246.13) 1880(1908) bytes of data. ping: local error: message too long, mtu=1500 Rasmus