Ethernet link up up, cannot ping device behind port

I had this problem a few weeks ago and can't explain what I saw/experienced.

We had a device which was connected via Fiber , but it was not pingable, even thou the interface status was up up. After the onsite engineer decided to replace the fiber cable we could suddenly ping the end device (no config changes/faults in gateway and subnetmask etc....). If something went wrong with the fiber cable, why would it show as up up and why did the ICMP message did not reach the device?

So it seem like the signal was srtong enough to get an up up, but not to get the ping across?? Can someone explain how this works...

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Comments

Hondabuff

This is why UDLD was invented.

FrankGuthrie

Does this also run on end devices such as Camera's? Is it a given it runs on anything supporting fiber?

Hondabuff

Only on the fiber ports. Here is good video that explains it. https://www.youtube.com/watch?v=ivXCDghnjTM