正解:B
Bidirectional Forwarding Detection (BFD) is a protocol designed to detect faults between two forwarding engines connected by a link. In the context of Cisco SD-WAN, BFD is used to measure link quality by rapidly detecting link failures, which is crucial for maintaining the high availabilityand reliability of the network. BFD operates independently of media, data protocols, and routing protocols, providing a low-overhead, fast method of detecting failures in the path between adjacent routers.
References:
* Cisco documentation on SD-WAN solutions, specifically the sections discussing BFD and its role in link quality measurement.
* Cisco's official training and certification materials for Implementing and Operating Cisco Service Provider Network Core Technologies (SPCOR).