The Company XYZ network requires OSPF dead neighbor detection in a subsecond manner.

When Bidirectional Forwarding Detection (BFD) is not available, OSPF can still achieve subsecond convergence using the OSPF fast hello feature.

Fast hello allows the configuration of OSPF hello/dead intervals to subsecond values (e.g., hello = 100ms, dead = 300ms).

This accelerates OSPF’s ability to detect neighbor failures based on missed hello packets without relying on external mechanisms like BFD.

Why other options are incorrect:

A. STP (Spanning Tree Protocol) is unrelated to OSPF and is used at Layer 2.

C. LFA (Loop-Free Alternate) is a fast reroute technique but does not affect neighbor failure detection.

D. DPD (Dead Peer Detection) is used in VPN technologies (e.g., IPsec) and not applicable in OSPF.

Fast hello is fully aligned with CCDE v3.1 under “Protocol Design Implications” and is a commonly recommended method for improving IGP convergence performance when BFD is not an option.

==========