Spanning Tree Protocol (continued)

Necessity of generating a tree

The routing selection protocol, such as rip, can prevent loops on the network layer. However, there is nothing to do with the L2 loop router, so there is a spanning tree protocol.

Role 1: logically prevents Loops

2. When the main link goes down, the blocked port is enabled to implement the backup link function.

The generation tree uses BPDU for information exchange. There are two types of BPDU:

Configure the BPDU package and topology change announcement BPDU package

Under normal circumstances, the switch will only receive BPDU packets from its root port.

When the topology of A vswitch changes, a TCN packet is sent to the root bridge from the root port.

Generate relationship between trees and VLANs

IEEE General Spanning Tree CST runs STP in units of switches. The advantage of CST is that the number of BPDU packets is reduced.

Cisco uses an independent pvst for each VLAN. Because the L2 VLAN is not connected, the optimal path is selected for each VLAN through pvst, but the disadvantage is that

Large switch Load

Cisco pvst + is compatible with ieee cst and allows CST to pass messages to pvst

650) This. width = 650; "src =" http://s3.51cto.com/wyfs02/M00/4D/95/wKioL1RTpsLx3rs2AACM1qreaMI777.jpg "Title =" area.jpg "alt =" wkiol1rtpslx3rs2aacm1qreami777.jpg "/>

IEEE defines RSTP (Rapid Spanning-Tree Protocol)

This protocol is based on STP

Due to the slow speed of STP port status convergence

Two Port roles are added to RSTP.

Alternate port this port serves as the backup port of the root Port

Backup port this port serves as the backup port of the specified port

Meanwhile, the STP status is reduced to discarding, learning, and forwarding.

RSTP fast convergence mechanism is divided into three types

1. Protocol/Agreement Mechanism

2. Fast root port switching

3. Edge port Introduction

End!

This article from the "Indomitable" blog, please be sure to keep this source http://changbo.blog.51cto.com/1316452/1570589

Spanning Tree Protocol (continued)