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Spanning Tree Understanding

Spanning Tree Understanding. Based on IEEE802.1D-1998 Edition. By Morning Mencius. Content. Why to use Spanning Tree? Spanning Tree figure Spanning Tree Algorithm Implementation of STA Q&A. Why to use Spanning Tree?. Spanning Tree Algorithm 运行的必要条件.

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Spanning Tree Understanding

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  1. Spanning Tree Understanding Based on IEEE802.1D-1998 Edition By Morning Mencius

  2. Content • Why to use Spanning Tree? • Spanning Tree figure • Spanning Tree Algorithm • Implementation of STA • Q&A

  3. Why to use Spanning Tree?

  4. Spanning Tree Algorithm运行的必要条件 • Bridge的Port有5种状态Disabled, Blocking, Listening, Learning, Forwarding • 每个switch都会处理目地址为MAC group address(01-80-c2-00-00-00)的frame • 每个switch都有一个唯一的ID • 每个switch的每个PORT都有一个唯一的PORT ID

  5. Spanning Tree Algorithm运行的参数 • Root Bridge ,交换网络中Bridge ID最小的switch • TransmissionCost,传输速度越快,该port的TC越小 • Path Cost: • Root Port,switch上唯一一个通向Root Bridge方向的Port • Root Path Cost • Designated Port,LAN上唯一一个通向Root Bridge方向cost最小的Port • Designated Bridge,LAN上拥有Designated Port的Bridge

  6. Spanning Tree Algorithm运行的时间参数 • Forward Delay,一个frame经过所有的bridge所需的最长时间 • Message Age,root bridge所发出的BPDU frame已生存的时间 • Maximum Age,frame的最大生存时间 • Hello Time,root bridge产生问候frame的时间间隔

  7. Spanning Tree Algorithm的基本方法 • 通过不断的发送hello frame交换信息 • 选root bridge,Bridge ID最小的 • 选root port,Root Path Cost最小,Port ID最小 • 选designate port,Path cost最小,Bridge ID最小的 • 简单模拟一下STP的工作过程(flash)

  8. BPDU frame Bit8 – Topology Change Acknowledgment flag Bit1 -- Topology Change flag

  9. 抓包获得的BPDU

  10. 两种BPDU的数据结构

  11. 记录Bridge信息的数据结构

  12. 记录Port信息的数据结构

  13. STP协议实体的数据

  14. STP初始化 认为自己为root bridge,向所有端口发BPDU STP协议的初始化 • 认为自己是root bridge 将所有端口设为Blocking状态 并设置为指定端口 将指定端口设置为Listening 默认每2s向所有指定端口上发BPDU

  15. 某个端口上接到BPDU received_config_bpdu(port_no, BPDU) { /* 端口的指定root大于BPDU中的root */ /* 端口的指定cost大于BPDU中的root path cost */ /* 端口的指定bridge大于BPDU中的bridge id */ /* 端口的指定port大于BPDU中的port id */ if (supersedes_port_info(port_no, BPDU)) { /*将BPDU中的信息记录到端口数据port_info中*/ record_config_information(port_no, config); configuration_update(); /* 更新协议的配置 */ port_state_selection(); /* 重新设置端口状态 */ if (port_no == bridge_info.root_port) { /* 记录下BPDU中time信息到bridge_info中 */ record_config_timeout_values(config); config_bpdu_generation(); /* 向所有指定端口发包*/ } else if (designated_port(port_no)) { reply(port_no); /* 回复对方自己信息 */ } }

  16. Topology Change

  17. 默认参数表

  18. 生成树协议的发展 • STP/RSTP • PVST/PVST+ • MISTP/MSTP

  19. Q&A • 支持STP的switch端口有哪几种状态? • 在使用STP的网络中每一个switch都有一个root port,R(right) or W(wrong)? • STP使用的BPDU (目的MAC为01-80-c2-00-00-00)封包有哪几种类型？

  20. 4.如图运行STP的网络正常工作时, a.哪个bridge为root bridge? b.哪些端口为root port? c.哪些端口为designated port d.哪个端口是blocking状态?

  21. Q&A 5.如图运行STP的网络正常工作时, a.哪个bridge为root bridge? b.哪些端口为root port? c.哪些端口为designated port d.哪些端口是blocking状态?

  22. THANKS

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