Which OSPF feature allows a router with redundant route processors to maintain its OSPF state
and adjacencies across planned and unplanned RP switchovers and does this by checkpointing
state information from OSPF on the active RP to the standby RP? This feature does not require
the OSPF neighbor to support graceful restart.

A.
NSR

B.
NSF

C.
BFD

D.
MTR

E.
SDR

Explanation:

Continuous Forwarding
An important aspect of high availability is maintenance of traffic forwarding, even in the case of
control-plane switchovers. Cisco IOS XR Software has several built-in features that can provide
continuous forwarding, including RSP stateful switchover (SSO), Nonstop Forwarding (NSF),
Graceful Restart, and NSR.
NSF: Cisco IOS XR Software supports forwarding without traffic loss during a brief outage of the
control plane through signaling and routing protocol implementations for Graceful Restart
extensions as standardized by the IETF. In addition to standards compliance, this implementation
has been compatibility tested with Cisco IOS Software and third-party operating systems.
Graceful Restart: This control-plane mechanism ensures high availability by allowing detection
and recovery from failure conditions while preserving NSF services. Graceful
Restart is a way to recover from signaling and control-plane failures without affecting the
forwarding plane. Cisco IOS XR Software uses this feature and a combination of check pointing,
mirroring, RSP redundancy, and other system resiliency features to recover prior to timeout and
avoid service downtime as a result of network reconvergence.
NSR: This feature allows for the forwarding of data packets to continue along known routes while
the routing protocol information is being refreshed following a processor switchover.
NSR maintains protocol sessions and state information across SSO functions for services such as
Multiprotocol Label Switching (MPLS) VPN. TCP connections and the routing protocol sessions
are migrated from the active RSP to the standby RSP after the RSP failover without letting the
peers know about the failover. The sessions terminate locally on the failed RSP, and the protocols
running on the standby RSP reestablish the sessions after the standby RSP goes active, without
the peer detecting the change. You can also use NSR with Graceful Restart to protect the routing
control plane during switchovers. The Cisco IOS XR Operating System provides system resiliency
through a comprehensive set of high-availability features including modularity, process restart,
fault handling, continuous forwarding, and upgradability.