SFP Fibre Connection not comming up

[Gaborius]

Hello everyone,
first of thank you all for your ideas and help beforehand.

Devices:

• two Cisco Catalyst 2960-X WS-C2960X-48LPS-L (names: SW1, SW2)
• one Cisco Catalyst 2960-X WS-C2960X-24PS-L (name: SW3)

Situation:
I want to connect SW1 to SW3 via SFP fibre and SW2 to SW3 via SFP fibre; but the status stays Link down Protocol down.

Configuration:
=====SW3======| 15.2(7)E4 |=====| C2960X-UNIVERSALK9-M |=====
interface GigabitEthernet1/0/25
   switchport trunk allowed vlan 3,9,18,81
   switchport mode trunk
   switchport nonegotiate
interface GigabitEthernet1/0/26
   switchport trunk allowed vlan 3,9,18,81
   switchport mode trunk
   switchport nonegotiate
=====SW2======| 15.2(7)E3 |=====| C2960X-UNIVERSALK9-M |=====
interface GigabitEthernet1/0/52
   switchport trunk allowed vlan 3,9,18,81
   switchport mode trunk
   switchport nonegotiate
=====SW1======| 15.2(7)E3 |=====| C2960X-UNIVERSALK9-M |=====
interface GigabitEthernet1/0/52
   switchport trunk allowed vlan 3,9,18,81
   switchport mode trunk
   switchport nonegotiate

What I tried so far:

• Donkey ear on SW3 via port 25 and 26; worked fine and came up directly
• Connection from SW1 P52 to SW2 P52; worked fine and came up directly
• Fibre cable test and check; all clean and fully working
• Interface inventory check on all three switches; all SFPs are shown up (had to be, since point 1 and 2 worked out but I still checked it)
• Connection from SW1 P52 to SW3 P25; not working
• Connection from SW1 P52 to SW3 P26; not working
• Connection from SW2 P52 to SW3 P25; not working
• Connection from SW2 P52 to SW3 P26; not working
• Setting all 4 interfaces on default and reconfigure them; no changes to previous points.

Additonal information:
There are also cupper connections between the switches as trunks and running rstp; these connections working fine and with no issues.

So has anyone an idea why the SFP connections / interfaces are acting so weirdly? Or do I miss anything? I am sitting on that issue since two days now, searching the internet, trying out step by step configurations/test and i still can't wrap my mind around it.
Also if you need more information I would be glad to provide you with those.

Kind regards and take care all of you,
Gabor

[Gaborius]

Okay, I tried it and well it works. So thanks a lot ... even though I don't get it since I used the same setup of patching to run the connection between SW1 and SW2 for the test, there it worked with no issues.

[andrewswanson]

I've seen patch panels where some links are straight through and others crossed - very confusing and usually the first thing I check when there is no link up on a given pair

Andy

[Gaborius]

Well I will do that from now on as well, thats for sure.

Thanks again and have a nice one.

Gabor

[Gaborius]

A different thought I have, could it be possible that the ISO can be an issue? Since 15.2(7)E3 is running on SW1/SW2 and 15.2(7)E4 on SW3... on the IOS side I am kinda lost so could anyone of you provide me an answer if that is an possible issue? On the internet I don't find much other than the IOS realse notes which doesn't cover any SFP bugs, so far I can tell.