Troubleshoot: Why there’s no lights for both switches?

by Cyrus Lok on Wednesday, May 12, 2010 at 2:57am

No lights for both my 3550 ports and 2950 ports after I connected both ports with cross over cable

3550:
3550-2#sh int status

Port Name Status Vlan Duplex Speed Type
Fa0/1 connected 1 a-full a-100 10/100BaseTX
Fa0/2 notconnect 1 auto auto 10/100BaseTX
<output truncated>

3550-2#sh run interface fa0/2
Building configuration…

Current configuration : 68 bytes
!
interface FastEthernet0/2
switchport mode dynamic desirable
end

port fa0/2 of 3550 is in default mode: dynamic desirable.

2950:
Port Name Status Vlan Duplex Speed Type
Fa0/1 connected trunk a-full a-100 10/100BaseTX
Fa0/2 err-disabled 10 auto auto 10/100BaseTX
Fa0/3 err-disabled 10 auto auto 10/100BaseTX
<output truncated>

2950-2#sh int status err

Port Name Status Reason
Fa0/2 err-disabled bpduguard
Fa0/3 err-disabled bpduguard

Previously I have configured bpduguard on both fa0/2 and fa0/3 and I forgot. Now both fa0/2 and 3 are in error disabled state.

To solve this:
2950-2(config)#int fa0/2
2950-2(config-if)#no spanning-tree bpduguard
2950-2(config-if)#shut
2950-2(config-if)#no shut
2950-2(config-if)#
2950-2(config-if)#
00:14:13: %LINK-3-UPDOWN: Interface FastEthernet0/2, changed state to up
00:14:14: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/2, changed state to up

Ok now fa0/2 has light. 3550 port also has light.

Now I will fix fa0/3
Enter configuration commands, one per line. End with CNTL/Z.
2950-2(config)#int fa0/3
2950-2(config-if)#no spann
2950-2(config-if)#no spanning-tree bpdug
2950-2(config-if)#no spanning-tree bpduguard
2950-2(config-if)#shut
2950-2(config-if)#no shut
2950-2(config-if)#do sh int status err

show interface status errdisabled does not have output which means no more error disabled ports.