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Miller" , Jakub Kicinski , Jonathan Corbet , , Subject: [PATCH net-next] doc: Document unexpected tcp_l3mdev_accept=1 behavior Date: Thu, 19 Aug 2021 17:38:54 +0900 Message-ID: <20210819083854.156996-1-bpoirier@nvidia.com> X-Mailer: git-send-email 2.32.0 MIME-Version: 1.0 X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 42ff079a-d112-4382-2dc6-08d962ed4f65 X-MS-TrafficTypeDiagnostic: BN6PR1201MB2546: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:10000; X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.112.35;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:schybrid04.nvidia.com;CAT:NONE;SFS:(4636009)(136003)(346002)(396003)(376002)(39860400002)(46966006)(36840700001)(2906002)(6916009)(26005)(186003)(8936002)(6666004)(2616005)(86362001)(5660300002)(478600001)(47076005)(426003)(7696005)(82310400003)(54906003)(70206006)(70586007)(336012)(316002)(83380400001)(1076003)(36756003)(82740400003)(7636003)(356005)(4326008)(36860700001)(8676002);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Aug 2021 08:42:42.7368 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 42ff079a-d112-4382-2dc6-08d962ed4f65 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.35];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: DM6NAM11FT021.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN6PR1201MB2546 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: kuba@kernel.org As suggested by David, document a somewhat unexpected behavior that results from net.ipv4.tcp_l3mdev_accept=1. This behavior was encountered while debugging FRR, a VRF-aware application, on a system which used net.ipv4.tcp_l3mdev_accept=1 and where TCP connections for BGP with MD5 keys were failing to establish. Cc: David Ahern Signed-off-by: Benjamin Poirier Reviewed-by: David Ahern --- Documentation/networking/vrf.rst | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/Documentation/networking/vrf.rst b/Documentation/networking/vrf.rst index 0dde145043bc..0a9a6f968cb9 100644 --- a/Documentation/networking/vrf.rst +++ b/Documentation/networking/vrf.rst @@ -144,6 +144,19 @@ default VRF are only handled by a socket not bound to any VRF:: netfilter rules on the VRF device can be used to limit access to services running in the default VRF context as well. +Using VRF-aware applications (applications which simultaneously create sockets +outside and inside VRFs) in conjunction with ``net.ipv4.tcp_l3mdev_accept=1`` +is possible but may lead to problems in some situations. With that sysctl +value, it is unspecified which listening socket will be selected to handle +connections for VRF traffic; ie. either a socket bound to the VRF or an unbound +socket may be used to accept new connections from a VRF. This somewhat +unexpected behavior can lead to problems if sockets are configured with extra +options (ex. TCP MD5 keys) with the expectation that VRF traffic will +exclusively be handled by sockets bound to VRFs, as would be the case with +``net.ipv4.tcp_l3mdev_accept=0``. Finally and as a reminder, regardless of +which listening socket is selected, established sockets will be created in the +VRF based on the ingress interface, as documented earlier. + -------------------------------------------------------------------------------- Using iproute2 for VRFs