7.2 RSTP

1.基本概念

STP收敛慢,端口定义繁琐,对网络拓扑变化依赖计时器。

RSTP(快速生成树)对STP进行了优化,收敛速度快,能兼容STP。

2.RSTP接口角色

包含根接口、指定接口、替代接口、备份接口。

1)替代接口

图片[1]-7.2 RSTP-大赛人网
图7-6  RSTP替代接口网络拓扑
[SW3]display stp brief 
MSTID  Port                        Role  STP State     Protection
0    GigabitEthernet0/0/2        ROOT  FORWARDING      NONE
0    GigabitEthernet0/0/3        ALTE  DISCARDING      NONE
GigabitEthernet0/0/3为阻塞接口,是根接口的备份。

2)备份接口

一台设备上由于收到了自己所发的BPDU从而被阻塞的接口。

3.RSTP接口状态

丢弃Discarding、学习Learning、转发Forwarding

4.边缘接口

连接终端设备的接口不需要参与STP生成树计算,可以设置为边缘接口(Edge Port),可以立即切换到转发状态。

图片[2]-7.2 RSTP-大赛人网
图7-7  RSTP边缘接口网络拓扑
[SW2]interface GigabitEthernet 0/0/1
[SW2-GigabitEthernet0/0/1]stp edged-port enable 
[SW2]interface GigabitEthernet 0/0/2
[SW2-GigabitEthernet0/0/2]stp edged-port enable 
[SW2]interface GigabitEthernet 0/0/3
[SW2-GigabitEthernet0/0/3]stp edged-port enable 

5.P/A机制

RSTP通过Proposal/Agreement(提议/同意)机制保证一个指定接口从丢弃状态快速进入转发状态,加快了生成树收敛。

6.保护功能

1)BPDU保护

边缘接口收到BPDU后会变成一个普通接口,引发RSTP重新计算,影响网络,在交换机激活BPDU保护功能后如果边缘接口收到BPDU,则交换机会立即把接口关闭(Error-Down),并触发告警信息。

图片[3]-7.2 RSTP-大赛人网
图7-8  RSTP边缘接口激活BPDU保护网络拓扑

(1)边缘端口配置

[SW2]interface GigabitEthernet 0/0/1
[SW2-GigabitEthernet0/0/1]stp edged-port enable 
[SW2]interface GigabitEthernet 0/0/2
[SW2-GigabitEthernet0/0/2]stp edged-port enable 
[SW2]interface GigabitEthernet 0/0/3
[SW2-GigabitEthernet0/0/3]stp edged-port enable 

(2)边缘端口激活BPDU保护配置

[SW2]stp bpdu-protection
[SW2]display stp brief
MSTID  Port                        Role  STP State     Protection
0    GigabitEthernet0/0/1        DESI  FORWARDING      BPDU
0    GigabitEthernet0/0/2        DESI  FORWARDING      BPDU
0    GigabitEthernet0/0/3        DESI  FORWARDING      BPDU
0    GigabitEthernet0/0/24       ROOT  FORWARDING      NONE

(3)BPDU保护接口自动恢复配置

手动恢复端口(undo shutdown)或设置自动恢复
[SW2]error-down auto-recovery cause bpdu-protection interval 30

2)根保护

根桥是可抢占的,重新计算RSTP会对网络造成影响,开启根保护功能会规避以上问题。
[SW1]interface GigabitEthernet 0/0/24
[SW1-GigabitEthernet0/0/24]stp root-protection 
[SW1]display stp brief 
MSTID  Port                        Role  STP State     Protection
0    GigabitEthernet0/0/24       DESI  FORWARDING      ROOT

3)环路保护

图片[4]-7.2 RSTP-大赛人网
图7-9  RSTP环路保护网络拓扑

(1)RSTP基本配置

[SW1]stp mode rstp 
[SW1]stp  priority 0
[SW2]stp mode rstp 
[SW3]stp mode rstp 
[SW3]display stp brief 
MSTID  Port                        Role  STP State     Protection
0    GigabitEthernet0/0/2        ROOT  FORWARDING      NONE
0    GigabitEthernet0/0/3        ALTE  DISCARDING      NONE

(2)指定接口配置环路保护

[SW3]interface GigabitEthernet 0/0/2
[SW3-GigabitEthernet0/0/2]stp loop-protection 
[SW3]display stp brief              
 MSTID  Port                        Role  STP State     Protection
0    GigabitEthernet0/0/2        ROOT  FORWARDING      LOOP
0    GigabitEthernet0/0/3        ALTE  DISCARDING      NONE

(3)替代接口配置环路保护

[SW3]interface GigabitEthernet 0/0/3
[SW3-GigabitEthernet0/0/3]stp loop-protection 
[SW3]display stp brief              
MSTID  Port                        Role  STP State     Protection
0    GigabitEthernet0/0/2        ROOT  FORWARDING      LOOP
0    GigabitEthernet0/0/3        ALTE  DISCARDING      LOOP

(4)拓扑变更保护

[SW3]stp tc-protection 

7.RSTP配置

图片[5]-7.2 RSTP-大赛人网
图7-10  RSTP基本配置网络拓扑

1)RSTP基本配置

(1)基本配置

[SW1]stp mode rstp 
[SW1]stp root primary 
[SW1]stp enable
[SW2]stp mode rstp 
[SW2]stp root secondary 
[SW2]stp enable
[SW3]stp mode rstp 
[SW3]stp enable
[SW4]stp mode rstp 
[SW4]stp enable
[SW4]display stp brief 
MSTID  Port                        Role  STP State     Protection
0    GigabitEthernet0/0/3        ALTE  DISCARDING      NONE
0    GigabitEthernet0/0/4        ROOT  FORWARDING      NONE

(2)修改GigabitEthernet 0/0/4COST值,配置GigabitEthernet 0/0/4为阻塞端口

[SW4]interface GigabitEthernet 0/0/4
[SW4-GigabitEthernet0/0/4]stp cost 100000
[SW4]display stp brief              
MSTID  Port                        Role  STP State     Protection
0    GigabitEthernet0/0/3        ROOT  FORWARDING      NONE
0    GigabitEthernet0/0/4        ALTE  DISCARDING      NONE

[SW4]display stp interface GigabitEthernet 0/0/4
-------[CIST Global Info][Mode RSTP]-------
CIST Bridge         :32768.4c1f-cc04-10c3
Config Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
Active Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
CIST Root/ERPC      :0    .4c1f-cc28-59ea / 40000
CIST RegRoot/IRPC   :32768.4c1f-cc04-10c3 / 0
CIST RootPortId     :128.3
BPDU-Protection     :Disabled
TC or TCN received  :26
TC count per hello  :0
STP Converge Mode   :Normal 
Time since last TC  :0 days 0h:3m:2s
Number of TC        :12
Last TC occurred    :GigabitEthernet0/0/3
----[Port4(GigabitEthernet0/0/4)][DISCARDING]----
 Port Protocol       :Enabled
 Port Role           :Alternate Port
 Port Priority       :128
 Port Cost(Dot1T )   :Config=100000 / Active=100000
 Designated Bridge/Port   :4096.4c1f-ccb4-211f / 128.4
 Port Edged          :Config=default / Active=disabled
 Point-to-point      :Config=auto / Active=true
 Transit Limit       :147 packets/hello-time
 Protection Type     :None
 Port STP Mode       :RSTP                
 Port Protocol Type  :Config=auto / Active=dot1s
 BPDU Encapsulation  :Config=stp / Active=stp
 PortTimes           :Hello 2s MaxAge 20s FwDly 15s RemHop 0
 TC or TCN send      :1                   
 TC or TCN received  :3                   
 BPDU Sent           :2                   
          TCN: 0, Config: 0, RST: 2, MST: 0
 BPDU Received       :208                 
          TCN: 0, Config: 0, RST: 208, MST: 0
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