300-420 question 4: Refer to the exhibit. A network engineer needs to enhance the exist…

Q4Advanced Addressing and Routing Solutions

Refer to the exhibit. A network engineer needs to enhance the existing IS-IS environment. The Catalyst switch has dual supervisors. Whenever a stateful switchover takes place, the network undergoes unnecessary route recomputation. Which solution resolves this problem when the upstream router does not support graceful restart messaging?

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Community votes

67% (6)

33% (3)

0% (0)

Discussion · 15

B 8

Selected Answer: B the correct one is B (NSR) NSF is also called gracefull restart. And the router does not understand GR.

B 4

Selected Answer: B Graceful Restart (GR) (also known as Non Stop Forwarding (NSF)) and Non Stop Routing (NSR) are two different mechanisms to stop routing protocol re-convergence during a processor switchover. When Graceful Restart (NSF) is used, peer networking devices are informed, via protocol extensions before the event (so peers should also be NSF (GR) capable). The peer routers know about a failure and so will give the switching over router a "grace" period to re-establish the neighbor relationship, while continuing to forward 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 moved 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 needed to support Graceful Restart. Following this logic, the answer is B (NSR)

Actually, NSF does not exchange any GR messages with its peer ( so NSF is the correct answer) And NSR does exchange 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

Its the other way around. NSF uses the GR mechanism, not NSR.

It's B. Check my comment on this with information from OCG page 168.

C 2

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

B 1

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

B 1

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

sorry, i meant to choose Option C. NSR is vendor specific and may not be supported everywhere.

So which one is the correct answer. For me it feels more like 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 notice that there was a switchover

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

C 1

Selected Answer: C Correct answer is C. After a supervisor engine switchover, NSF's main goal is to keep forwarding IP traffic. To reduce the amount of time a network is unavailable to its users after a switchover, NSF works together with SSO. SSO is always used by Cisco NSF, which provides redundancy for Layer 3 communications.

C 1

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

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

B 1

Selected Answer: B ------------------------------NSR ------------------------------------------------------- --tries to keep neighbor adjacencies up during an RP failover. --does not need cooperation from neighbors (unlike GR), so the neighbors are not aware that an RP failover is taking place. --Besides checkpointing the FIB, routing protocol state information is also checkpointed to the standby RP. answer is B (since the upstream device does not understand GR)