What failure does a first-hop redundancy protocol protect the network against?

First-hop redundancy protocols (FHRPs) like HSRP, VRRP, and GLBP are designed to ensure network availability by providing a redundant default gateway for end devices. If the active router serving as the default gateway fails, an FHRP automatically switches traffic to a standby router, preventing a complete loss of connectivity for the subnet. BGP neighbor flapping relates to routing protocol stability, not first-hop redundancy. Spanning-tree loops are prevented by STP, which addresses Layer 2 forwarding issues. Root-bridge loss is a concern for STP convergence, not the default gateway for end devices.