Exam 300-420 topic 1 question 36 discussion

the correct answer is B (NSR) NSF is also known as gracefull restart. And the router does not understand GR.

Non-Stop Routing (NSR) is a Cisco proprietary feature similar to NSF, but it requires support on both the switch and the upstream router. The question states that the upstream router doesn't understand graceful restart messaging, so NSR won't work.

Everyone is voting B, but all the answers are are explaining C. The very last mssage of the question says the upstream router doesnt understand graceful restart. So we must use NSR instead

Repeating again... it's C. NSR helps for a graceful restart (GR). But our scenario is SSO (Stateful Switchover), where NSF is used.

Correct answer is C. After a supervisor engine switchover, NSF's primary goal is to keep forwarding IP traffic. To reduce the amount of time a network is inaccessible to its users after a switchover, NSF collaborates with SSO. SSO is always used by Cisco NSF, which offers redundancy for Layer 3 communications.

NSR is correct IMO for this reason - NSR is for control plane and NSF is for data plane. wherever you need forwarding you should choose NSF and wherever you need Routing convergence , you should choose NSR.

So which one is the correct answer. For me it feels more to be NSR, as the neighbor router does not understand GR. And gr are exchanged through routing protocol IS-IS. So with NSR the neighbor will not understand that there was a switchover

i stick also with B NSR is an internal (vendor-specific) mechanism to extend the awareness of routing to the standby routing plane so that in case of failover, the newly active routing plane can take charge of the already established sessions. https://www.ciscopress.com/articles/article.asp?p=1395746&seqNum=2

Graceful Restart (GR) (also known as Non Stop Forwarding (NSF)) and Non Stop Routing (NSR) are two different mechanisms to prevent routing protocol re-convergence during a processor switchover. When Graceful Restart (NSF) is used, peer networking devices are informed, via protocol extensions prior to the event (so peers should also be NSF (GR) capable). The peer routers are aware of a failure and so will give the switching over router a "grace" period to re-establish the neighbor relationship, while continuing to forward to the routes from that peer. When NSR is used, peer networking devices have no knowledge of any event on the switching over router. All information needed to continue the routing protocol peering state is transferred to the standby processor so it can "pick up" immediately upon a switchover. NSR is desirable in cases where the routing protocol peer doesn't support the RFCs necessary to support Graceful Restart. Following this logic, the answer is B (NSR)

https://community.cisco.com/t5/xr-os-and-platforms/nsr-nsf-and-graceful-restart/td-p/2212355

Actually, NSF does not exchange any GR messages with it's peer ( so NSF is the correct answer) And NSR is indeed exchanging GR messages with the peer ( So its the incorrect answer) Source: https://forum.huawei.com/enterprise/en/difference-between-nsr-nsf-and-gr/thread/601106-861