Which high-availability routing feature requires the neighbor router to support the graceful restart capability?

Which high-availability routing feature requires the neighbor router to support the graceful restart
capability?

A.
BFD

B.
NSR

C.
NSF

D.
MTR

Explanation:
On Cisco IOS XR software, NSF minimizes the amount of time a network is unavailable to its users
following a route processor (RP) failover. The main objective of NSF is to continue forwarding IP
packets and perform a graceful restart following an RP failover.
When a router restarts, all routing peers of that device usually detect that the device went down and
then came back up. This transition results in what is called a routing flap, which could spread across
multiple routing domains. Routing flaps caused by routing restarts create routing instabilities, which
are detrimental to the overall network performance. NSF helps to suppress routing flaps in NSFaware devices, thus reducing network instability.
NSF allows for the forwarding of data packets to continue along known routes while the routing
protocol information is being restored following an RP failover. When the NSF feature is configured,
peer networking devices do not experience routing flaps. Data traffic is forwarded through
intelligent line cards while the standby RP assumes control from the failed active RP during a
failover. The ability of line cards to remain up through a failover and to be kept current with the
Forwarding Information Base (FIB) on the active RP is key to NSF operation.
When the Cisco IOS XR router running IS-IS routing performs an RP failover, the router must perform
two tasks to resynchronize its link-state database with its IS-IS neighbors. First, it must relearn the
available IS-IS neighbors on the network without causing a reset of the neighbor relationship.
Second, it must reacquire the contents of the link-state database for the network.
The IS-IS NSF feature offers two options when configuring NSF:
•IETF NSF
•Cisco NSF
If neighbor routers on a network segment are NSF aware, meaning that neighbor routers are running
a software version that supports the IETF Internet draft for router restartability, they assist an IETF
NSF router that is restarting. With IETF NSF, neighbor routers provide adjacency and link-state
information to help rebuild the routing information following a failover.
In Cisco IOS XR software, Cisco NSF checkpoints (stores persistently) all the state necessary to
recover from a restart without requiring any special cooperation from neighboring routers. The state
is recovered from the neighboring routers, but only using the standard features of the IS-IS routing
protocol. This capability makes Cisco NSF suitable for use in networks in which other routers have
not used the IETF standard implementation of NSF