connecting two 3750G-12S-S

[gvysk]

just trying to test the ports by pinging from one switch to the other. Reset both switches to default. Both switches are running IOS version 12.2 (55)SE8. GLC-SX-MM on both ends. Working fiber cable.(I tested the cable and the two sfp in a different switch setup). The ports do not come up. If I plug both sfp into the same switch they will come up. The ports see the SFP is inserted. I then tried to set the ports up as trunks manually. No go. I read about the speed nonegotiate command so tried that. The port will come up briefly but then err-disable with link-flap. I am probably missing something basic here.

Thanks in advance.

Greg

[Leo Laohoo]

I then tried to set the ports up as trunks manually.

How is this possible.  No one can configure speed/duplex settings on a fibre optic module. 

The port will come up briefly but then err-disable with link-flap

What is the result to the command "sh interface status error"? 

Try the age-old method:  Connect one channel of the SFP to the other.  Did the port go UP or not?

[gvysk]

The command does not change the speed. I believe it just tells the port not to negotiate with the other end. Yes,the port comes up with a loop back plug. It also comes up when I connect two different ports on the same switch. Just won't come up connecting switch to switch. Will see what the status shows when I have access to them again. Thanks

[Leo Laohoo]

If loopback plug works, then are you sure both SFP are of the same wavelength?

[gvysk]

Yes, they are both GLC-SX-MM. The same fiber optic cable and the 2 sfp work connecting a 3560 to a wireless lan controller port. That is what is weird. I thought maybe is has something to do with the 3750G-12S-S being a SFP only switch and therefore has a different setup somehow. I thought it should just automatically form a trunk when I connect port1 from sw1 to port 1 on sw2 after i set the switches back to factory default.

[Leo Laohoo · Accepted solution]

Could be the SFP or could be one of the SFP port on the 3750G-12S could be faulty.  

[gvysk]

I had tried port1-sw1 to port1-sw2. Then I tried port2-sw1 to port2-sw2. I figured both ports on both switches can't be bad but I was wrong. On a whim I tried port4-sw1 to port4-sw2 and guess what? It came up. I have never seen switches bad like this before where it lights up with a loopback but not on a actual connection to another switch. Thanks for the help Leo.

[Leo Laohoo]

Thanks for taking the time to rate our posts and updates.  

Can I ask you to do something?  Can you reboot either one or both of the switches and then post the output to the command "sh post"?  If something is broken, then it should show up here.  

[gvysk]

Both switches show all post tests passed

Switch#sh post
Stored system POST messages:

Switch 1
---------

POST: CPU MIC register Tests : Begin
POST: CPU MIC register Tests : End, Status Passed

POST: PortASIC Memory Tests : Begin
POST: PortASIC Memory Tests : End, Status Passed

POST: CPU MIC interface Loopback Tests : Begin
POST: CPU MIC interface Loopback Tests : End, Status Passed

POST: PortASIC RingLoopback Tests : Begin
POST: PortASIC RingLoopback Tests : End, Status Passed

POST: PortASIC CAM Subsystem Tests : Begin
POST: PortASIC CAM Subsystem Tests : End, Status Passed

POST: PortASIC Stack Port Loopback Tests : Begin
POST: PortASIC Stack Port Loopback Tests : End, Status Passed

POST: PortASIC Port Loopback Tests : Begin
POST: PortASIC Port Loopback Tests : End, Status Passed

[Leo Laohoo]

Ok.  Thanks for the output.

[gvysk]

Turns out the switches both have bad capacitors in the same spots, causing the same ports on both to be bad. That is probably why a loopback plug worked where cabling switch to switch did not. The caps are not totally blown, just bulging. I am going to replace the caps and will let you know how it turns out.

[Leo Laohoo]

Ok.  I presume you can't RMA the switch?

[gvysk]

no, can't rma. Replaced the caps and now all the ports come up normally.