STP 實驗

 

 

 

 

stp 網絡中 存在一個根橋，其他交換機爲分根橋。根橋是stp 網絡的邏輯中心，非根橋是根橋的下游設備，當根橋發生故障，費根橋之前交互信息後選舉新的根橋，交互的信息稱爲BPDU。


stp 定義三種端口角色：指定端口，根端口和預備端口

指定端口：是交換機向所連網段轉發配置BPDU的端口，每個網段只能有一個指定端口。一般情況下，根橋的每個端口都是指定端口

根端口： 是非根交換機去往根橋路徑最優的端口。在一個運行STP協議的交換機上最多隻有一個根端口，但根橋上沒有根端口

預備端口： 如果個端口既不是指定端口也不是根端口，則此端口爲預備端口。預備端口將被阻塞。


根橋選舉： 橋ID，有橋優先級和mac地址組成


###開啓stp
#stp mode stp
[SW1]stp mode stp 
[SW1]dis stp 

<SW4>dis stp
-------[CIST Global Info][Mode STP]-------
CIST Bridge         :32768.4c1f-cc49-7893
Config Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
Active Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
CIST Root/ERPC      :32768.4c1f-cc49-7893 / 0
CIST RegRoot/IRPC   :32768.4c1f-cc49-7893 / 0
CIST RootPortId     :0.0
BPDU-Protection     :Disabled
TC or TCN received  :5
TC count per hello  :0
STP Converge Mode   :Normal 
Time since last TC  :0 days 0h:1m:10s
Number of TC        :10
Last TC occurred    :GigabitEthernet0/0/3

-------[CIST Global Info][Mode STP]-------
CIST Bridge         :32768.4c1f-cc6d-4399
Config Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
Active Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
CIST Root/ERPC      :32768.4c1f-cc49-7893 / 20000
CIST RegRoot/IRPC   :32768.4c1f-cc6d-4399 / 0
CIST RootPortId     :128.4
BPDU-Protection     :Disabled
TC or TCN received  :62
TC count per hello  :0
STP Converge Mode   :Normal 
Time since last TC  :0 days 0h:2m:7s
Number of TC        :18
Last TC occurred    :GigabitEthernet0/0/4

<SW2>dis stp
-------[CIST Global Info][Mode STP]-------
CIST Bridge         :32768.4c1f-ccfb-2981
Config Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
Active Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
CIST Root/ERPC      :32768.4c1f-cc49-7893 / 20000
CIST RegRoot/IRPC   :32768.4c1f-ccfb-2981 / 0
CIST RootPortId     :128.4
BPDU-Protection     :Disabled
TC or TCN received  :289
TC count per hello  :0
STP Converge Mode   :Normal 
Time since last TC  :0 days 0h:2m:37s
Number of TC        :21
Last TC occurred    :GigabitEthernet0/0/4


<SW1>dis stp 
-------[CIST Global Info][Mode STP]-------
CIST Bridge         :32768.4c1f-cc9f-5efe
Config Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
Active Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
CIST Root/ERPC      :32768.4c1f-cc49-7893 / 20000
CIST RegRoot/IRPC   :32768.4c1f-cc9f-5efe / 0
CIST RootPortId     :128.4
BPDU-Protection     :Disabled
TC or TCN received  :181
TC count per hello  :0
STP Converge Mode   :Normal 
Time since last TC  :0 days 0h:0m:43s
Number of TC        :19
Last TC occurred    :GigabitEthernet0/0/4

###sw1 的角色是非根橋

[SW1]dis stp brief
 MSTID  Port                        Role  STP State     Protection
   0    GigabitEthernet0/0/1        DESI  FORWARDING      NONE
   0    GigabitEthernet0/0/2        ALTE  DISCARDING      NONE
   0    GigabitEthernet0/0/3        DESI  FORWARDING      NONE
   0    GigabitEthernet0/0/4        ROOT  FORWARDING      NONE

確認SW4 是根橋，因爲只有根橋都是指定端口
 
[SW4]dis stp brief
 MSTID  Port                        Role  STP State     Protection
   0    GigabitEthernet0/0/1        DESI  FORWARDING      NONE
   0    GigabitEthernet0/0/2        DESI  FORWARDING      NONE
   0    GigabitEthernet0/0/3        DESI  FORWARDING      NONE
[SW4]

上述4臺交換機 橋ID 比較，優先級數字越小，優先級越高，優先級相同，則比較MAC 地址，mac地址越小，優先級越大


根端口選舉

非根交換機在選舉根端口分別依據該端口的根路徑開銷、對端BID(Bridge ID )、對端PID(Port ID) 和本端PID



指定端口選舉

首先比較累計路徑開銷，累計路徑開銷最小的端口就是指定端口。如果累計路徑開銷相同，則比較端口所在交換機的橋ID,所在橋ID最小的端口被選舉爲指定端口。
如果通過累計路徑端口和所在橋ID選舉不出來，則比較端口ID，端口ID最小的被選定位指定端口。

備註： 只有指定端口和根端口可以轉發數據。其他端口爲預備端口，被阻塞，不能轉發數據。





##指定開銷標準
[SW1]stp pathcost-standard ?
  dot1d-1998  IEEE 802.1D-1998
  dot1t       IEEE 802.1T
  legacy      Legacy



[SW1]stp pathcost-standard dot1t 
###disp stp 查看 開銷標準 
Port Cost(Dot1T )   :Config=auto / Active=20000


[SW1]inter GigabitEthernet 0/0/1
[SW1-GigabitEthernet0/0/1]stp cos	
[SW1-GigabitEthernet0/0/1]stp cost ?
  INTEGER<1-200000000>  Port path cost
###設置端口開銷
[SW1-GigabitEthernet0/0/1]stp cost 200000
[SW1-GigabitEthernet0/0/1]di th
#
interface GigabitEthernet0/0/1
 stp instance 0 cost 200000
#
return
[SW1-GigabitEthernet0/0/1]
###確認
 Port Cost(Dot1T )   :Config=200000 / Active=200000
 
 ###設置權限 修改後發現這個變成 根橋 
 [SW1]stp priority 8192
[SW1]
[SW1]di stp
-------[CIST Global Info][Mode STP]-------
CIST Bridge         :8192 .4c1f-cc9f-5efe
Config Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
Active Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
CIST Root/ERPC      :8192 .4c1f-cc9f-5efe / 0
CIST RegRoot/IRPC   :8192 .4c1f-cc9f-5efe / 0

[SW1]dis stp brief
 MSTID  Port                        Role  STP State     Protection
   0    GigabitEthernet0/0/1        DESI  FORWARDING      NONE
   0    GigabitEthernet0/0/2        DESI  FORWARDING      NONE
   0    GigabitEthernet0/0/3        DESI  FORWARDING      NONE
   0    GigabitEthernet0/0/4        DESI  FORWARDING      NONE
   
##修改成值，
 [SW1]stp priority 32768
[SW1]dis stp brief
 MSTID  Port                        Role  STP State     Protection
   0    GigabitEthernet0/0/1        DESI  FORWARDING      NONE
   0    GigabitEthernet0/0/2        ALTE  DISCARDING      NONE
   0    GigabitEthernet0/0/3        DESI  FORWARDING      NONE
   0    GigabitEthernet0/0/4        ROOT  FORWARDING      NONE
[SW1]