STP Spanning Tree initialization and convergence analysis of Switch configuration

Build tree initialization and Convergence

STP establishes a root node, called the root bridge, and constructs a topology in which each node in the network can arrive at only one path, the final generated tree originated from the root node. redundant links that are not part of the shortest path tree will be blocked because such paths are blocked, therefore, it is possible to implement a non-loop topology. When a data frame is received on the blocked link, it is discarded.

STP needs network devices to exchange messages to detect bridging loops,VswitchA message sent to build a non-loop topology is called a Bridge Protocol Data Unit. The blocked port continuously receives BPDU to ensure that a new spanning tree can still be calculated when the active path or device fails. BPDU provides sufficient information. All switches can use this information to complete the following tasks: select a separate switch as the root of the Spanning Tree. Calculate the shortest path from itself to the root switch.

For each lan cidr Block, specify a vswitch as the nearest switch, which is called the specified switch. Specify the switch to process all communications from the LAN to the root switch. Each non-root switch selects its own port as the root port, which is the shortest interface to the root switch path. Select a port that is part of the spanning tree as the specified port on each CIDR block. unspecified ports will be blocked.

1. STP four-step initialization principle:

When establishing a non-loop logical topology, STP must follow the four-step STP initialization principle, namely:

Step 1: The lowest root BID.

Step 2: The lowest path overhead is to the root bridge.

Step 1: The lowest sender BID.

Step 2: lower port ID.

When a bridge device is powered on, it sends BPDU to all ports at a frequency of 2 seconds at the Hello Time interval. The bridge uses the preceding four steps to determine that each port has the highest BPDU priority. If you have the highest priority, send the peer. Otherwise, stop sending and accept the peer's BPDU. If you fail to receive the BPDU with a higher priority from the other party within 20 seconds, you can resend the BPDU to confirm the optimal BPDU.

2. Three Steps for Spanning Tree convergence

When all the switches are powered on, all the bridges send BPDU information to the connection port, and then immediately enter the STP non-loop logical topology computing. The spanning tree can be divided into three steps from topology initialization to convergence into a non-loop topology.

Step 2: Select Root Bridge). The only Root Bridge is elected.

Step 2: Select Root Ports). Other bridges calculate a series of Root Ports.

Step 2: select the specified port Designated ports) For CIDR block connection.

The introduction of the initialization and convergence of the Spanning Tree is over. I hope that you have understood the above content and we will continue to organize this knowledge for you.