%SPANTREE-6-PORT_STATE: Port Gi0/23 instance 2 moving from forwarding to disabled

[johnnynextiraone]

Working on this fault on behalf of a customer and looking for help.  (E-mail from customer below)

We have a 2960 access switch that has two uplinks to the core;  one uplink goes to core switch 1 (6509), and the second uplink goes to core switch 2 (6509).  This was working fine, for a few years, until December 24, when one of the two uplinks failed.  I have replaced all physical layer components, but this has not resolved.  I have noticed on a few occassions that when the failed uplink does come up the remaining working one goes down.  There are no errdisable msgs in the logs but there are some STP msgs (below).

I am sure this is a config issue, but cannot see what is causing one uplink port to constantly shutdown.  Also confused as to why port moves to disabled from forwarding and the interface changes to updown.  Port 23 is the faulty port.

Jan  3 15:14:43 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/23, changed state to up

Jan  3 15:14:43 GMT: %SPANTREE-6-PORT_STATE: Port Gi0/23 instance 2 moving from blocking to forwarding

Jan  3 15:14:44 GMT: %SPANTREE-6-PORT_STATE: Port Gi0/23 instance 301 moving from blocking to forwarding

Jan  3 15:20:08 GMT: %SPANTREE-6-PORT_STATE: Port Gi0/23 instance 2 moving from forwarding to disabled

Jan  3 15:20:08 GMT: %SPANTREE-6-PORT_STATE: Port Gi0/23 instance 301 moving from forwarding to disabled

Jan  3 15:20:09 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/23, changed state to down

[pshivkumar]

In my case it was the speed. I set it to 10/half.

[foleyequipment]

Why would you set any connection to 10/half to fix that problem?  You have a connected device that only runs at 10/half ?  

[paul driver]

Hello
Your issue seem to suggest possible physical issue with between core 1 and the access switch, Can you post the output of the following please:

LON-BSG-0-SW01
sh run int Gi0/23
sh run int Gi0/24
sh ip interface brief
sh interface status
sh int trunk

Core 1 & 2 (6509)
sh run int gig2/23
sh run int vlan 2
sh run int vlan 301
sh ip interface brief
sh interface status
sh int trunk