STP 实验

 

 

 

 

stp 网络中 存在一个根桥，其他交换机为分根桥。根桥是stp 网络的逻辑中心，非根桥是根桥的下游设备，当根桥发生故障，费根桥之前交互信息后选举新的根桥，交互的信息称为BPDU。


stp 定义三种端口角色：指定端口，根端口和预备端口

指定端口：是交换机向所连网段转发配置BPDU的端口，每个网段只能有一个指定端口。一般情况下，根桥的每个端口都是指定端口

根端口： 是非根交换机去往根桥路径最优的端口。在一个运行STP协议的交换机上最多只有一个根端口，但根桥上没有根端口

预备端口： 如果个端口既不是指定端口也不是根端口，则此端口为预备端口。预备端口将被阻塞。


根桥选举： 桥ID，有桥优先级和mac地址组成


###开启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 的角色是非根桥

[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

确认SW4 是根桥，因为只有根桥都是指定端口
 
[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台交换机 桥ID 比较，优先级数字越小，优先级越高，优先级相同，则比较MAC 地址，mac地址越小，优先级越大


根端口选举

非根交换机在选举根端口分别依据该端口的根路径开销、对端BID(Bridge ID )、对端PID(Port ID) 和本端PID



指定端口选举

首先比较累计路径开销，累计路径开销最小的端口就是指定端口。如果累计路径开销相同，则比较端口所在交换机的桥ID,所在桥ID最小的端口被选举为指定端口。
如果通过累计路径端口和所在桥ID选举不出来，则比较端口ID，端口ID最小的被选定位指定端口。

备注： 只有指定端口和根端口可以转发数据。其他端口为预备端口，被阻塞，不能转发数据。





##指定开销标准
[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 开销标准 
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
###设置端口开销
[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]
###确认
 Port Cost(Dot1T )   :Config=200000 / Active=200000
 
 ###设置权限 修改后发现这个变成 根桥 
 [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]