A network technician has just run a new point-to point fiber link between two local routers, however, after the fiber has been plugged in on both ends, the interface will not come up.
The technician has double-checked the interface configuration on both routers, both SFPs have been hard looped to confirm they are functioning, connectors on both ends of the links have been cleaned, and there is sufficient optical power. Which of the following is the cause of the issue?