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Cisco switch not acting right

Posted on 2013-01-17
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Last Modified: 2013-01-17
On a new install of a WS-C2960S-48TS-L.  The switch has 4 SFP ports.  I have other Cisco switches with the same SFP port module this one has and am fimiliar with them.  The documentation claims I am using the correct SFP module.  

I installed a new GLC-SX-MM module in one of the ports and connected it to a SFP port on my WS-C2960G-24TC-L.  Here is what happens:

C2960S (new) - Gi1/0/50 1000 BaseSX SFP Status: Port is disabled.

C2960G  (existing) - Gi0/23 1000 Base SX SFP Status: Link up  Speed 1000 mbps  Duplex Full.

I can't find any way to get it to work.  I have disabled and enabled the port without luck. I have used different SFP modules in different ports.  Same result.

Is the switch defective?
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Question by:skkinney
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LVL 11

Expert Comment

by:rharland2009
ID: 38788773
It sounds remarkably like the port is blocking.
Do a sh spanning-tree blockedports while the interface in question is connected.
Do a sh spanning-tree gi1/0/50 as well.
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Author Comment

by:skkinney
ID: 38788834
CS-G-830-1>sh spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32768
             Address     0009.5bb3.c8c9
             Cost        20004
             Port        1 (GigabitEthernet1/0/1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     5897.1ea7.5000
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------
Gi1/0/1             Root FWD 4         128.1    P2p
Gi1/0/8             Desg FWD 4         128.8    P2p
Gi1/0/14            Desg FWD 4         128.14   P2p
Gi1/0/30            Desg FWD 4         128.30   P2p
Gi1/0/33            Desg FWD 4         128.33   P2p
Gi1/0/34            Desg FWD 4         128.34   P2p
Gi1/0/35            Desg FWD 4         128.35   P2p
Gi1/0/47            Desg FWD 4         128.47   P2p
Gi1/0/48            Desg FWD 4         128.48   P2p
Gi1/0/50            Altn BLK 4         128.50   P2p
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LVL 11

Expert Comment

by:rharland2009
ID: 38788867
It's blocking - BLK tells us that.
Before you unblock it, find out why it's doing this - and by that I mean find out what loop you're being protected from by spanning-tree.
If you want redundant links, etc. I would suggest configuring the links as Etherchannel.
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Author Comment

by:skkinney
ID: 38788938
So you are saying it is protecting itself, probably from loopback?  I have no other direct connections to the other switch.  There is a third switch involved that provides an indirect link.  Could this be the problem?

How do I unblock it?
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Accepted Solution

by:
Don Johnston earned 500 total points
ID: 38789056
How do I unblock it?
You could unplug the G1/0/1 port. It's blocking G1/0/50 because there's another path to the root.  Spanning-tree has determined that the best path to the root is out the G1/0/1 port.
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Author Comment

by:skkinney
ID: 38789066
OK, so that confirms the third switch is the problem.  Thanks for your help.
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LVL 11

Expert Comment

by:rharland2009
ID: 38789095
You're welco-oh wait, you weren't thanking me....guess I gave you zero info that helped. Good times!
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Expert Comment

by:Don Johnston
ID: 38789114
Yeah... These points should go to rharland2009.
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Author Comment

by:skkinney
ID: 38789124
Oh, I am so sorry.  I wasn't paying attention.  How do we get the points to the correct person?
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LVL 11

Expert Comment

by:rharland2009
ID: 38789142
Don't sweat it...I was just being snarky. Glad you got your gear rockin.
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