From patchwork Thu Nov 23 13:45:48 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Hangbin Liu X-Patchwork-Id: 13466268 X-Patchwork-Delegate: kuba@kernel.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="F5w1wGAR" Received: from mail-pg1-x52d.google.com (mail-pg1-x52d.google.com [IPv6:2607:f8b0:4864:20::52d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F30A3F9 for ; Thu, 23 Nov 2023 05:46:29 -0800 (PST) Received: by mail-pg1-x52d.google.com with SMTP id 41be03b00d2f7-5c2066accc5so628160a12.3 for ; Thu, 23 Nov 2023 05:46:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1700747189; x=1701351989; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=wDbV4TqVpQY3WWJc+DEqiCW2ek6jh/ijW23lPWhz1m0=; b=F5w1wGARnk8pK8thL+m6BvHAsSb4L39tqnGXCOkT/2OopZQ39nbAVblzKSZ1iUkd81 QyUSuoFgVDqoc0hX6BsZ739FJwximEy0/PzLCUwf8KbAtKTkNB/9eR4pDKnlvq6J83v/ 4P5ykSDLBVjde+x/ehLg3N2LNu0ldhtBCtQsjrv8mn34DzhNqXkrnlzkkX/Qr5HorJ2n xbTPuLZVRPI7t4Pklv6Cg+rAY4S7Rz7/S+fEROkJoEkdwW0wwYBcL/PLLOxGbfnzgiPS DhXvxKIBVYtAgVvbK8+hxdoFC52OimO0MgelLy8fgsITy0MHpHyB1EHH5YcAXpdQonSl pv/Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1700747189; x=1701351989; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=wDbV4TqVpQY3WWJc+DEqiCW2ek6jh/ijW23lPWhz1m0=; b=DM9cmgqZ0dIHfI8ni33odmLsc116ToauaGxnC5NX76OOFP/CEn61vPwsx48/U9CDMS ENk598XjycbKtb7+5oRd+WWOthXdxL6E4aV4p+cFuzhsnieurgO5VSQxCjqNL5FF29US JFBiicRKS/TWta3K8uzQt5LhW5JwQF2m0qUdJYjn/aM423nPRhq6qdMRIEFmFfnnlMTc gvwiI6ri5XjLGYyKlZJOKyRUWlw+kN5jE2aLnzdRQycXa+kRks8IdlcD9ZSOYsetCyRV C88GmbBVnwIDqYnGjgRj+U32LOEk3BFWF43YEc0t2U7gSnsDEdie9U5lqnJaP7ZyBs7s KkIw== X-Gm-Message-State: AOJu0Yx9wkuahoUVX3Zz6Cg9Lxt3X8f0R53T+AA5PFycnNCgjGQz3BZ2 94j2wKUQ1557P7wMsdVMvK8vhoyOx81d/zqe X-Google-Smtp-Source: AGHT+IGp2UvAqedWM1WdpELsQ15s9O5ug8vy4pnoOSAQLb/+ttVFrHjRKSJmBrbKzuCjZkj2PDZ0sg== X-Received: by 2002:a17:90a:1951:b0:280:a01a:906a with SMTP id 17-20020a17090a195100b00280a01a906amr5687128pjh.5.1700747188919; Thu, 23 Nov 2023 05:46:28 -0800 (PST) Received: from Laptop-X1.redhat.com ([43.228.180.230]) by smtp.gmail.com with ESMTPSA id 29-20020a17090a195d00b0028328057c67sm1414210pjh.45.2023.11.23.05.46.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Nov 2023 05:46:28 -0800 (PST) From: Hangbin Liu To: netdev@vger.kernel.org Cc: "David S . Miller" , David Ahern , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Ido Schimmel , Nikolay Aleksandrov , Roopa Prabhu , Stephen Hemminger , Florian Westphal , Andrew Lunn , Florian Fainelli , Vladimir Oltean , Jiri Pirko , Marc Muehlfeld , Hangbin Liu Subject: [PATCHv2 net-next 05/10] docs: bridge: add STP doc Date: Thu, 23 Nov 2023 21:45:48 +0800 Message-ID: <20231123134553.3394290-6-liuhangbin@gmail.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20231123134553.3394290-1-liuhangbin@gmail.com> References: <20231123134553.3394290-1-liuhangbin@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: kuba@kernel.org Add STP part for bridge document. Signed-off-by: Hangbin Liu --- Documentation/networking/bridge.rst | 85 +++++++++++++++++++++++++++++ 1 file changed, 85 insertions(+) diff --git a/Documentation/networking/bridge.rst b/Documentation/networking/bridge.rst index 84aae94f6598..1fd339e48129 100644 --- a/Documentation/networking/bridge.rst +++ b/Documentation/networking/bridge.rst @@ -51,6 +51,91 @@ options are added. .. kernel-doc:: net/bridge/br_sysfs_br.c :doc: Bridge sysfs attributes +STP +=== + +The STP (Spanning Tree Protocol) implementation in the Linux bridge driver +is a critical feature that helps prevent loops and broadcast storms in +Ethernet networks by identifying and disabling redundant links. In a Linux +bridge context, STP is crucial for network stability and availability. + +STP is a Layer 2 protocol that operates at the Data Link Layer of the OSI +model. It was originally developed as IEEE 802.1D and has since evolved into +multiple versions, including Rapid Spanning Tree Protocol (RSTP) and +`Multiple Spanning Tree Protocol (MSTP) +`_. + +Bridge Ports and STP States +--------------------------- + +In the context of STP, bridge ports can be in one of the following states: + * Blocking: The port is disabled for data traffic and only listens for + BPDUs (Bridge Protocol Data Units) from other devices to determine the + network topology. + * Listening: The port begins to participate in the STP process and listens + for BPDUs. + * Learning: The port continues to listen for BPDUs and begins to learn MAC + addresses from incoming frames but does not forward data frames. + * Forwarding: The port is fully operational and forwards both BPDUs and + data frames. + * Disabled: The port is administratively disabled and does not participate + in the STP process. The data frames forwarding are also disabled. + +Root Bridge and Convergence +--------------------------- + +In the context of networking and Ethernet bridging in Linux, the root bridge +is a designated switch in a bridged network that serves as a reference point +for the spanning tree algorithm to create a loop-free topology. + +Here's how the STP works and root bridge is chosen: + 1. Bridge Priority: Each bridge running a spanning tree protocol, has a + configurable Bridge Priority value. The lower the value, the higher the + priority. By default, the Bridge Priority is set to a standard value + (e.g., 32768). + 2. Bridge ID: The Bridge ID is composed of two components: Bridge Priority + and the MAC address of the bridge. It uniquely identifies each bridge + in the network. The Bridge ID is used to compare the priorities of + different bridges. + 3. Bridge Election: When the network starts, all bridges initially assume + that they are the root bridge. They start advertising Bridge Protocol + Data Units (BPDU) to their neighbors, containing their Bridge ID and + other information. + 4. BPDU Comparison: Bridges exchange BPDUs to determine the root bridge. + Each bridge examines the received BPDUs, including the Bridge Priority + and Bridge ID, to determine if it should adjust its own priorities. + The bridge with the lowest Bridge ID will become the root bridge. + 5. Root Bridge Announcement: Once the root bridge is determined, it sends + BPDUs with information about the root bridge to all other bridges in the + network. This information is used by other bridges to calculate the + shortest path to the root bridge and, in doing so, create a loop-free + topology. + 6. Forwarding Ports: After the root bridge is selected and the spanning tree + topology is established, each bridge determines which of its ports should + be in the forwarding state (used for data traffic) and which should be in + the blocking state (used to prevent loops). The root bridge's ports are + all in the forwarding state. while other bridges have some ports in the + blocking state to avoid loops. + 7. Root Ports: After the root bridge is selected and the spanning tree + topology is established, each non-root bridge processes incoming + BPDUs and determines which of its ports provides the shortest path to the + root bridge based on the information in the received BPDUs. This port is + designated as the root port. And it is in the Forwarding state, allowing + it to actively forward network traffic. + 8. Designated ports: A designated port is the port through which the non-root + bridge will forward traffic towards the designated segment. Designated ports + are placed in the Forwarding state. All other ports on the non-root + bridge that are not designated for specific segments are placed in the + Blocking state to prevent network loops. + +STP ensures network convergence by calculating the shortest path and disabling +redundant links. When network topology changes occur (e.g., a link failure), +STP recalculates the network topology to restore connectivity while avoiding loops. + +Proper configuration of STP parameters, such as the bridge priority, can +influence which bridge becomes the Root Bridge. Careful configuration can +optimize network performance and path selection. + FAQ ===