Hello We had a 100G link that started to misbehave and caused the customers to notice bad packet loss. The optical values are just fine but we had packet loss and latency. Interface shows FEC errors on one end and carrier transitions on the other end. But otherwise the link would stay up and our monitor system completely failed to warn about the failure. Had to find the bad link by traceroute (mtr) and observe where packet loss started. The link was between a Juniper MX204 and Juniper ACX5448. Link length 2 meters using 2 km single mode SFP modules. What is the best practice to monitor links to avoid this scenarium? What options do we have to do link monitoring? I am investigating BFD but I am unsure if that would have helped the situation. Thanks, Baldur