为什么只有根桥发送bpdu_BPDU的完整形式是什么？

为什么只有根桥发送bpdu

BPDU：网桥协议数据单元 (BPDU: Bridge Protocol Data Unit)

BPDU is an abbreviation of the "Bridge Protocol Data Unit".

BPDU是“网桥协议数据单元”的缩写 。

It is a data message in the form of a frame that used to exchange or transmits information within an organized superfluous Local Area Network (LAN) by using a MAC address from its source of basis port to the Multicast address. BPDU consists of information regarding the spanning tree protocol which is required to organize and keep up its topology. It also consists of information about switches, ports, port priority, costs, and addresses. In a local area network topology, the data messages are transmitted across bridges to identify loops. After identification of loops, preferred bridge interfaces are then close down to eradicate loops and putting down superfluous switch ports in the state of backup support or blocked state.

它是帧形式的数据消息，用于通过使用从其基本端口源到多播地址的MAC地址在有组织的多余的局域网(LAN)中交换或传输信息。 BPDU包含有关生成树协议的信息，这是组织和保持其拓扑结构所必需的。它还包含有关交换机，端口，端口优先级，成本和地址的信息。在局域网拓扑中，数据消息跨网桥传输以标识环路。识别出环路之后，然后关闭首选的网桥接口以消除环路，并使多余的交换机端口处于备份支持或阻塞状态。

BPDU的处理 (Processing of BPDU)

In the transmission of BPDU, the transmission, in the beginning, does not begin instantly by devices which are connected to switch ports. By contrast, the devices progress through a variety of unusual conditions at the same time as the processing of transmission of BPDU resolves the network topology. After resolving the network topology, the Configured BPDU is transmitted by root bridges to make available data port information to the entire switches.
在BPDU的传输中，开始时，传输不会立即由连接到交换机端口的设备开始。相反，随着BPDU传输的处理解决了网络拓扑问题，设备同时经历了各种异常情况。解决网络拓扑后，已配置的BPDU由根网桥传输，以向整个交换机提供可用的数据端口信息。
A topology change notification (TCN) BPDU transmitted by bridges in the direction of the root bridges to inform further switches of port changes in the topology, such as port up or port down. The introduction of TCNs into the network is done by a non-root switch and transmitted to the root in the topology.
网桥在根网桥的方向上发送的拓扑更改通知(TCN) BPDU ，用于通知其他交换机拓扑中的端口更改，例如端口打开或端口关闭。将TCN引入网络是由非根交换机完成的，并传输到拓扑中的根。
When the TCN BPDU is received by root bridges, then there will be a topology change done by the root switch to lay down a topology change flag in its standard BPDU. This flag is transmitted instantly to the entire additional switches to give a command to them to quickly age out their forwarding table opening
当根网桥接收到TCN BPDU时 ，根交换机将进行拓扑更改，以在其标准BPDU中放置一个拓扑更改标志。此标志立即传输到所有其他交换机，以发出命令以使它们快速老化其转发表的开口

switches.
开关。