Does following scenario work? We have single mode fiber running between two building, but we have MMF patchcord connected to SPF (SFP-10GBase-SR).


I am seeing my interface is flapping but just wanted to make sure it whether it because of mixing fiber mode or something else.

3 Answers 3


Yes, this absolutely is a problem. Don't ever mix different types of cabling. Multimode has a 50 or 62.5 micron core diameter, while single mode fiber typically has a 9 micron core. If you connect two fibers with different core diameters, you'll lose a lot of the light going through the connector, resulting in a link flapping or being down.

  • Thanks for quick answer! i had doubt but better confirm with you guys! thanks
    – Satish
    Aug 8, 2016 at 22:45

Going from a multimode fiber or a lightsource designed for multimode fiber into single mode fiber will result in a very high loss.

You need to replace your patch cords with single mode ones and your transcievers with LR ones.


No we can not mix single mode and multi mode fiber cables due to difference core diameter in size

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