Exam 350-501 topic 1 question 245 discussion

D - Cisco Express Forwarding Study the link below It is not necessary to use OSPF, you can also use EIGRP or BGP so that is not the correct answer but "so that packets continue to be forwarded during failovers" you use Cisco Express Forwarding (CEF). "Cisco Express Forwarding A key element of NSF is packet forwarding. In a Cisco networking device, packet forwarding is provided by Cisco Express Forwarding. Cisco Express Forwarding maintains the Forwarding Information Base (FIB), and uses the FIB information that is current at the time of a switchover to continue forwarding packets during a switchover, to reduce traffic interruption during the switchover." https://www.cisco.com/c/dam/en/us/td/docs/switches/lan/catalyst9400/software/release/16-6/configuration_guide/stck_mgr_ha/b_166_nsf_sso_9400_cg.html

B. OSPF (Open Shortest Path First) is a routing protocol that maintains a link-state database (LSDB) to ensure consistent network routing. While OSPF can work with NSF to reduce convergence time during failover, simply implementing OSPF does not ensure packet forwarding during the switchover. The forwarding capability is managed by CEF in the context of NSF. NSF requires the routing protocol (like OSPF) to support NSF to avoid re-convergence, but OSPF alone is not sufficient to ensure packet forwarding during the failover. D. Cisco Express Forwarding (CEF) is a key component in maintaining packet forwarding during failovers when NSF is enabled. CEF allows the router to continue forwarding packets even if the control plane (routing protocols) is momentarily unavailable during a switchover. This makes CEF implementation crucial for NSF to function effectively, which is why this is the correct answer.

Comments for nottoday2077 are indeed an OPTION if you use OSPF but you can also use BGP or ISIS. I believe D is correct because whichever protocol you use "CEF is a mandatory prerequisite for NSF. "

For option B is more logical. Option A: Just by learning the Active and Standby state of the failover peer via L2VPN won't help to continue forwarding the traffic during switchover. Option C: Implementing VRF doesnt make sense Option D: CEF by default is already implemented. OSPF can use LSA 9 to inform its peer about the switchover.Type-9 LSAs are send to a neighbor with the GR flag set, as a part of the graceful-restart process. Devices must be NSF aware.

For this particular scenario since devices are separated in two DCs in different floors, the best option to work with NSF seems to be a L2VPN with a primary and backup link to converge fast. OSPF could be an option if using a failure detection mechanism like BFD, but it does not say it has it. CEF is a default protocol and works well with SSO for redundant supervisor modules on RP switches, but can't help much if the whole device go down. And I don't see how the VRF's option could possible help, again if the whole device fail. I go by option A, assuming we have redundant paths across those Data Centers, which is a MUST on today's networks.

From Cisco digital learning library, why no link: NSF-capable and NSF-aware peers cooperate using Graceful Restart extensions to BGP, OSPF, IS-IS, and EIGRP protocols. .... With the introduction of the LR-bit, an OSPF Cisco NSF router can discern whether an OSPF neighbor is capable of supporting its Cisco NSF procedures. When OSPF is operating and receiving hello packets with the presence of the LR-bit from its neighbors, it knows that the neighbor is NSF-aware and can execute the Cisco NSF procedures.

ANS is D: For NSF operation, routing protocols depend on Cisco Express Forwarding to continue forwarding packets while routing protocols rebuild the routing information. https://www.cisco.com/c/dam/en/us/td/docs/switches/lan/catalyst9400/software/release/16-6/configuration_guide/stck_mgr_ha/b_166_nsf_sso_9400_cg.html

B is correct. The only logic is that they can have connectivity during RP switchover between the campuses if they reside in a different location.

This questions doesn't make sense if it's about NSF. NSF does not help forwarding between separated devices as far as I am aware. Cisco says "The main objective of Cisco NSF is to continue forwarding IP packets following a route processor (RP) switchover. Usually, when a networking device restarts, all routing peers of that device detect that the device went down and then came back up" Any other ideas?