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交换技术 STP

Module 5-5. 交换技术 STP. 冗余的拓扑. 冗余的链路排除了单点故障的问题 . 冗余的链路导致广播风暴 , 重复帧 , 以及 MAC 地址表的不稳定。. 广播帧. Station D sends a broadcast frame. Broadcast frames are flooded to all ports except the originating port. 广播风暴. 主机 X 发送一个广播帧 . 交换机继续不断的传送广播帧. 重复帧. 主机 X 发送单播帧到路由器 Y.

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交换技术 STP

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  1. Module 5-5 交换技术 STP

  2. 冗余的拓扑 • 冗余的链路排除了单点故障的问题. • 冗余的链路导致广播风暴, 重复帧,以及MAC地址表的不稳定。

  3. 广播帧 • Station D sends a broadcast frame. • Broadcast frames are flooded to all ports except the originating port.

  4. 广播风暴 • 主机 X 发送一个广播帧. • 交换机继续不断的传送广播帧.

  5. 重复帧 • 主机X发送单播帧到路由器Y. • 如果交换机的MAC地址表中没有路由器Y的MAC地址. • 路由器将会收到两个相同的数据帧.

  6. MAC地址表的不稳定 • 主机X发送单播帧到路由器Y. • 路由器Y的MAC地址没有被交换机学习. • 交换机A 和 B从端口1中学习到主机X的MAC地址. • 但是发往路由器Y的数据帧被泛洪. • 交换机A和B错误的从端口2再次学习了主机X的MAC地址.

  7. 利用 STP 解决环路 • 通过将个别端口设置为blocking状态可以为网络提供一个无环的网络 • 它公布在IEEE 802.1D • Cisco 执行更强的PVST+

  8. Spanning-Tree 操作 • 每个广播域一个根桥. • 每个非根桥上一个根端口. • 每个网段上一个指定端口. • 为指派的端口不使用.

  9. STP 根桥的选举 • BPDU (default = sent every 2 seconds) • Root bridge = bridge with the lowest bridge ID • Bridge ID = Bridge Priority MAC Address

  10. Spanning-Tree 端口状态 Spanning tree transits each port through several different states:

  11. Uplinkfast / Backbonefast SwitchX(config)# spanning-tree uplinkfast • 用来在本地交换机上检测链路失效，并且能快速修复链路失效 ，一般只用于接入层交换机 SwitchX(config)# spanning-tree backbonefast • 用来在远端交换机上检测链路失效，一般可用于所有交换机

  12. PortFast PortFast 是配置在 access 上，而不是 trunk 端口.

  13. Configuring and Verifying PortFast SwitchX(config-if)# spanning-tree portfast • Configures PortFast on an interface OR SwitchX(config)# spanning-tree portfast default • Enables PortFast on all non-trunking interfaces SwitchX# show running-config interface interface • Verifies that PortFast has been configured on an interface

  14. BPDU护卫 / 过滤器 SwitchX(config-if)# spanning-tree bpduguard enable/disable • 在接入层交换机实用，允许接收BPDU SwitchX(config)# spanning-tree bpdufilter enable/disable • 当接收到BPDU则强制取消端口portfast

  15. Spanning-Tree Operation Example

  16. Spanning-Tree Path Cost

  17. Spanning-Tree Recalculation

  18. Per VLAN Spanning Tree Plus

  19. PVST+ 扩展的 桥 ID Bridge ID without the extended system ID Extended bridge ID with system ID System ID = VLAN

  20. Rapid Spanning Tree Protocol

  21. Default Spanning-Tree Configuration • Cisco 交换机三种类型的STPs: • PVST+ • PVRST+ • MSTP • 默认情况下在Cisco交换机上使用PVST+ : • 每个VLAN有一个独立的STP • 所有VLAN可以使用同一个交换机做根 • 但不等做负载均衡

  22. PVRST+ 配置指南 • Enable PVRST+. • 指定和配置交换机为根桥. • 指定和配置另一个交换机为备份的根桥. • 验证配置.

  23. PVRST+ 执行命令 SwitchX(config)# spanning-tree mode rapid-pvst • Configures PVRST+ SwitchX# show spanning-tree vlan vlan# [detail] • Verifies the spanning-tree configuration SwitchX# debug spanning-tree pvst+ • Displays PVST+ event debug messages

  24. 验证 PVRST+ SwitchX# show spanning-tree vlan 30 VLAN0030 Spanning tree enabled protocol rstp Root ID Priority 24606 Address 00d0.047b.2800 This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 24606 (priority 24576 sys-id-ext 30) Address 00d0.047b.2800 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 Interface Role Sts Cost Prio.Nbr Type -------- ----- --- --- -------- ---- Gi1/1 Desg FWD 4 128.1 P2p Gi1/2 Desg FWD 4 128.2 P2p Gi5/1 Desg FWD 4 128.257 P2p The spanning-tree mode is set to PVRST.

  25. Configuring the Root and Secondary Bridges

  26. Configuring the Root and Secondary Bridges: SwitchA SwitchA(config)# spanning-tree vlan 1 root primary • This command forces this switch to be the root for VLAN 1. SwitchA(config)# spanning-tree vlan 2 root secondary • This command configures this switch to be the secondary root for VLAN 2. OR SwitchA(config)# spanning-tree vlan # priority priority • This command statically configures the priority (increments of 4096).

  27. Configuring the Root and Secondary Bridges: SwitchB SwitchB(config)# spanning-tree vlan 2 root primary • This command forces the switch to be the root for VLAN 2. SwitchB(config)# spanning-tree vlan 1 root secondary • This command configures the switch to be the secondary root VLAN 1. OR SwitchB(config)# spanning-tree vlan # priority priority • This command statically configures the priority (increments of 4096).

  28. Summary • 冗余的交换网络拓扑包含多交换机和以太通道组 • 冗余的网络产生环路问题，例如广播风暴. • 使用STP生成无环路的网络拓扑. • 原始的STP被加强为PVST+和RSTP.

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