Which two features must be configured to perform AToM NSF? (Choose two)

FRR (Fast Reroute) is a mechanism for protecting MPLS TE tunnels against link or node failures by providing local repair paths, which is distinct from the control plane resilience offered by NSF.

Stateful Switchover (SSO) is a prerequisite for Nonstop Forwarding (NSF). SSO ensures that control plane information, including AToM pseudowire state and MPLS forwarding entries, is continuously synchronized between the active and standby Route Processors. This synchronization enables the standby RP to take over seamlessly as the active RP during a failover, maintaining data plane forwarding without interruption.

Distributed CEF (Cisco Express Forwarding) is a forwarding plane technology that allows line cards to perform packet forwarding independent of the main CPU, which enhances performance. While NSF relies on the forwarding plane, distributed CEF is not a specific configuration requirement to enable AToM NSF itself, but rather a performance-enhancing feature often present.

'Switch virtual path' refers to ATM-specific virtual circuit management and is not a general feature required for AToM NSF functionality.

Graceful Restart (GR) is essential for AToM NSF as it allows routing protocols (like BGP, OSPF, IS-IS) to signal to their neighbors that a control plane restart is occurring. Neighbors then continue to forward traffic using the stale routes until the restarting router fully recovers and re-establishes routing adjacencies, preventing a disruption in MPLS forwarding, including AToM pseudowires.