一个关于IOS软件引起的SPT 端口问题

本来是看一个题目觉得奇怪的,于是去查CISCO 文档,结果发现那个题目就是CISCO 文档上的东西.

只是这个文档本来是发布IOS  bug的一个通告,下面是关键内容.

Loopback Test: Test for a spanning-tree BPDU error. A crossover c able should be connected between two unused access ports. In this case, FastEthernet0/1 and FastEthernet0/2 are configured as access ports and are connected by a crossover cable. See for information on Ethernet RJ-45 crossover pinouts. The interface configuration is shown below:

Switch#show run interface FastEthernet0/1     

Building configuration...          

Current configuration : 72 bytes     

!     

interface FastEthernet0/1     

switchport mode access     

no ip address     

end          

Switch#show run interface FastEthernet0/2     

Building configuration...          

Current configuration : 72 bytes     

!     

interface FastEthernet0/2     

switchport mode access     

no ip address     

end

If, after 30 seconds, one of the port LEDs turns amber and the other stays green, the switch is working correctly, either because it does not have the problem or already has the Cisco IOS software upgrade that corrects the problem. If, after 30 seconds, both of the LEDs turn green and flash rapidly, the Cisco IOS software will need to be upgraded. This can also be verified by looking at the output from the following commands. If the switch is working correctly, the number of BPDUs received on the blocked port will be a non-zero number and will increase every two seconds, using the default timers

WORKING_Switch#show spanning-tree interface FastEthernet 0/1 detail     

Port 1 (FastEthernet0/1) of VLAN0001 is forwarding     

Port path cost 19, Port priority 128, Port Identifier 128.1.     

Designated root has priority 32769, address 000a.4107.7400     

Designated bridge has priority 32769, address 000a.4107.7400     

Designated port id is 128.1, designated path cost 0     

Timers: message age 0, forward delay 0, hold 0     

Number of transitions to forwarding state: 1     

BPDU: sent 237, received 1     

^^^^^^^^^^^^^^^^^^^^^^^^^^ Port is forwarding and sending BPDUs correctly. 

WORKING_Switch#show spanning-tree interface FastEthernet 0/2 detail     
Port 2 (FastEthernet0/2) of VLAN0001 is blocking     
Port path cost 19, Port priority 128, Port Identifier 128.2.     
Designated root has priority 32769, address 000a.4107.7400     
Designated bridge has priority 32769, address 000a.4107.7400     
Designated port id is 128.1, designated path cost 0     
Timers: message age 1, forward delay 0, hold 0     
Number of transitions to forwarding state: 0     
BPDU: sent 1, received 242     
^^^^^^^^^^^^^^^^^^^^^^^^^^ Port is blocking and receiving BPDUs correctly.
On a switch that is experiencing the problem, the number of BPDUs received on each port will stay at 0 (zero), 
and both ports will be forwarding.
PROBLEM_Switch#show spanning-tree interface FastEthernet 0/1 detail     
Port 1 (FastEthernet0/1) of VLAN0001 is forwarding     
Port path cost 19, Port priority 128, Port Identifier 128.1.     
Designated root has priority 32769, address 000a.4107.7400     
Designated bridge has priority 32769, address 000a.4107.7400     
Designated port id is 128.1, designated path cost 0     
Timers: message age 0, forward delay 0, hold 0     
Number of transitions to forwarding state: 1     
BPDU: sent 24, received 0     
^^^^^^^^^^^^^^^^^^^^^^^^^^ No BPDUs received. Port is forwarding.          
PROBLEM_Switch#show spanning-tree interface FastEthernet 0/2 detail     
Port 2 (FastEthernet0/2) of VLAN0001 is forwarding     
Port path cost 19, Port priority 128, Port Identifier 128.2.     
Designated root has priority 32769, address 000a.4107.7400     
Designated bridge has priority 32769, address 000a.4107.7400     
Designated port id is 128.2, designated path cost 0     
Timers: message age 0, forward delay 0, hold 0     
Number of transitions to forwarding state: 1     
BPDU: sent 26, received 0     
^^^^^^^^^^^^^^^^^^^^^^^^^^ No BPDUs received. Port is forwarding.
考811的战友应该对这个不陌生了