350-501 · Question #73
What is the main difference between the OSPF NSR and OSPF NSF mechanisms?
The correct answer is D. With NSR, the router that performs the switchover preserves the state internally. The main difference is that OSPF Nonstop Routing (NSR) preserves OSPF state internally during a switchover, unlike OSPF Nonstop Forwarding (NSF) which relies on neighbor assistance for state recovery.
Question
What is the main difference between the OSPF NSR and OSPF NSF mechanisms?
Options
- ANSR does not use as much memory resource as NSF does.
- BWith NSR, OSPF on the newly active standby RP initially has no state information.
- COn NSR, the neighbors must be NSR-aware.
- DWith NSR, the router that performs the switchover preserves the state internally.
How the community answered
(41 responses)- A7% (3)
- B2% (1)
- C2% (1)
- D88% (36)
Why each option
The main difference is that OSPF Nonstop Routing (NSR) preserves OSPF state internally during a switchover, unlike OSPF Nonstop Forwarding (NSF) which relies on neighbor assistance for state recovery.
NSR typically uses more memory resources than NSF because it needs to maintain a synchronized copy of the entire control plane state on the standby RP.
This statement is incorrect; with NSR, the newly active standby RP has complete state information because it has been synchronized with the active RP.
NSR does not require neighbors to be NSR-aware; it is an internal mechanism, while NSF often requires neighbors to be NSF-aware for graceful restart signaling.
With Nonstop Routing (NSR), the control plane state, including OSPF adjacency and topology information, is maintained and replicated between the active and standby Route Processors (RPs), allowing the standby RP to take over with full OSPF state already present.
Concept tested: OSPF NSR vs. NSF differences
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/15-mt/iro-15-mt-book/iro-nsr-ospf.html
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