The Curious Case of the Flapping Link...

Got a flapping link between 2 of my MLSwitch (both are Cisco 6800-XL).

int Te7/3 on MLS_1 to int Te7/1 on MLS_2

the fiber connector on MLS_1 is SC, while the fiber connector on MLS_2 is LC

I have changed the fiber cable (Single-mode LC-to-SC) and I have also changed the transceiver/module (10G-BASE-LR on MLS_1 and SFP-10G-SR) but it is still flapping.

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interestingly, only the int te7/3 shows flapping in its logs, while int Te7/1 on MLS_2 shows OSPF breaking/re-establishing (due obviously to the flapping link on the other end).

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on MLS_1, i assumed int Te7/3 is prolly faulty, so i moved the connection from int Te7/3 to int Te7/2, but after moving it, the flapping still occurs.

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# MLS_1 logs showing flapping

>Feb 22 10:40:42.832 pst: %LINK-3-UPDOWN: Interface TenGigabitEthernet7/3, changed state to up

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>Feb 22 10:40:42.932 pst: %LINEPROTO-5-UPDOWN: Line protocol on Interface TenGigabitEthernet7/3, changed state to up

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>Feb 22 10:55:14.942 pst: %LINK-3-UPDOWN: Interface TenGigabitEthernet7/3, changed state to down

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>Feb 22 10:55:15.022 pst: %LINEPROTO-5-UPDOWN: Line protocol on Interface TenGigabitEthernet7/3, changed state to down

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>Feb 22 10:56:19.446 pst: %LINK-3-UPDOWN: Interface TenGigabitEthernet7/2, changed state to down

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>Feb 22 10:56:20.530 pst: %LINK-3-UPDOWN: Interface TenGigabitEthernet7/2, changed state to up

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>Feb 22 10:56:20.630 pst: %LINEPROTO-5-UPDOWN: Line protocol on Interface TenGigabitEthernet7/2, changed state to up

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>Feb 22 11:07:46.111 pst: %LINK-3-UPDOWN: Interface TenGigabitEthernet7/2, changed state to down

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# MLS_2 logs showing OSPF breaking due to flapping

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>Feb 22 10:40:44.945 pst: %OSPFv3-5-ADJCHG: Process 10343, Nbr 192.168.1.1 on TenGigabitEthernet7/1 from LOADING to FULL, Loading Done

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>Feb 22 10:40:47.705 pst: %OSPF-5-ADJCHG: Process 10343, Nbr 192.168.1.1 on TenGigabitEthernet7/1 from LOADING to FULL, Loading Done

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>Feb 22 10:55:15.590 pst: %OSPFv3-5-ADJCHG: Process 10343, Nbr 192.168.1.1 on TenGigabitEthernet7/1 from FULL to DOWN, Neighbor Down: Interface down or detached

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>Feb 22 10:55:15.590 pst: %OSPF-5-ADJCHG: Process 10343, Nbr 192.168.1.1 on TenGigabitEthernet7/1 from FULL to DOWN, Neighbor Down: Interface down or detached

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>Feb 22 10:57:01.538 pst: %OSPF-5-ADJCHG: Process 10343, Nbr 192.168.1.1 on TenGigabitEthernet7/1 from LOADING to FULL, Loading Done

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>Feb 22 11:07:51.962 pst: %OSPF-5-ADJCHG: Process 10343, Nbr 192.168.1.1 on TenGigabitEthernet7/1 from LOADING to FULL, Loading Done

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The flapping lasts less than a second but it is enough to bring down ospf, and it turn it is disconnecting users who have sessions going on on that link.

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Anyone seen anything like this? I am stumped, I have tried everything.

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Should I change from a Single mode to a multimode fiber cable?

really appreciate any suggestions, thanks