You are designing a new multisite data center network within the same city. You are using the newest routers that run OSPF and DWDM point-to-point interfaces for site-to-site connectivity. Your primar

UDLD detects unidirectional fiber link conditions but operates at a higher software layer and is not the fastest mechanism compared to hardware-level optical LoS/AIS signals.

Interface event dampening is a stability feature that suppresses repeated link-state flaps to protect the routing protocol, not a failure detection mechanism.

Loss of Signal (LoS) and Alarm Indication Signal (AIS) are hardware-level optical fault notifications generated by the DWDM transceiver the instant the optical signal degrades or disappears. These events propagate at the physical layer without relying on any keepalive timer or protocol, so detection occurs in microseconds. This makes them faster than any software-driven mechanism such as sub-second BFD or fast-hello OSPF timers on DWDM interfaces.

Fast-hello timers reduce the OSPF dead interval to sub-second values but still depend on software timer expiration, making them inherently slower than immediate hardware-level optical fault signaling on DWDM links.