RSTP,讲述RSTP相较于STP的新增元素,如端口状态、端口角色、协商过程

1、 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-1Implementing Spanning TreeImplementing RSTP 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-2STP分类分类 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-3RSTP Port States 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03

2、-4RSTP Port States1） state状态上简化了 u discarding -忽略 disable -blocking -listening u learning - 构建mac-address-table u forwarding -转发数据 - Blocking，listening只能接收BPDU报文，进行生成树的选举，都不能做实质性的工作（包括构建MAC地址表，转发以太流量），所以在端口状态上做了简化 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-5Rapid Spanning Tree Protocol

3、 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-6RSTP Port Roles 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-7RSTP Port States2）端口的 role 角色扩展了概念 u RP ： root port 根端口 u DP ： designated port 指定端口 u NDP ： Non-designated-port 非指定端口 ： n AP ： alternative port 替代口 （NDP中作为RP备份接口） n BP

4、 ： backup port 备份口 （NDP中作为DP备份接口） uEP： edge-port 边缘口(不定义会造成30S收敛延迟) 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-8What Are Edge Ports? Will never have a switch connected to it Immediately transitions to forwarding Functions similarly to PortFast Configured by issuing the spanning-tree po

5、rtfast command 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-9RSTP Link Types 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-10RSTP summary cont 3） 制定了链路类型的概念（link-type） ： Half-duplex -shared (shr) Full-duplex - P2P (point-to-point) RSTP 中规定 P2P链路上采取 DP（指定端口）的协商选举机制，借助BPDU报文中FLA

6、G标记控制位的增强定义： proposal（提议） agreement（同意） 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-11RSTP BPDU Flag Byte Use 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-12RSTP BPDU Flag Byte Useu Port Role （flag 4th， 5th ） 表示 转发生成树BPDU报文的接口当前的角色 00-unknown 01-Alternative/backup 10-Root 11

7、-Designatedu Learning / forwarding （flag 3rd / 2nd） 用于描述端口的状态（learning，forwarding，discard）u proposal / agreement ( flag 6th / 1st ) RSTP 中规定 P2P链路上采取 DP（指定端口）的协商选举机制，借助BPDU报文中FLAG标记控制位的增强定义u Topo change / Topo change ACK （flag 0 / 7th） 优化拓补变更的扩散，加快网络收敛 2006 Cisco Systems, Inc. All rights reserved.BC

8、MSN v3.03-13RSTP Proposal and Agreement Process 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-14 Root and switch A synchronize. Ports on A come out of sync. Proposal or agreement takesplace between A and B.Downstream RSTP Proposal and Agreement 2006 Cisco Systems, Inc. All rights reserved

9、.BCMSN v3.03-15RSTP Topology Change Mechanism 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-16PVRST Implementation CommandsConfiguring spanning-tree mode rapid-pvstVerifying show spanning-tree vlan 101Debugging debug spanning-tree 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-1

10、7How to Implement Rapid PVRST 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-18Verifying PVRST Display spanning tree mode is set to PVRST.Switch# show spanning-tree vlan 30 VLAN0030Spanning tree enabled protocol rstpRoot ID Priority 24606Address 00d0.047b.2800This bridge is the rootHello T

11、ime 2 sec Max Age 20 sec Forward Delay 15 secBridge ID Priority 24606 (priority 24576 sys-id-ext 30) Address 00d0.047b.2800Hello Time 2 sec Max Age 20 sec Forward Delay 15 secAging Time 300Interface Role Sts Cost Prio.Nbr Type- - - - - -Gi1/1 Desg FWD 4 128.1 P2pGi1/2 Desg FWD 4 128.2 P2pGi5/1 Desg

12、FWD 4 128.257 P2p 2006 Cisco Systems, Inc. All rights reserved.BCMSN v3.03-19Summary RSTP provides faster convergence than 802.1D STP when topology changes occur. RSTP defines three port states: discarding, listening, and forwarding. RSTP defines five port roles: root, designated, alternate, backup, and disabled. Edge ports forward while topology changes occur. RSTP makes use of two link typesP2P and shared. 802.1w uses the BPDU differently from 802.1D. Convergence results from the proposal and agreement process conducted switch by switch. The RSTP topology change noti