Question 202 of 250 from exam 400-201: Cisco CCIE Service Provider Written Exam

Question 202 of 250 from exam 400-201: Cisco CCIE Service Provider Written Exam


What is the main difference between the OSPF NSR and OSPF NSF mechanisms?



A. B. C. D.


OSPF (Open Shortest Path First) is a popular routing protocol used in large-scale networks to exchange routing information between routers. Two mechanisms used to minimize disruption during network failures in OSPF are Non-Stop Routing (NSR) and Non-Stop Forwarding (NSF). These mechanisms work together to provide uninterrupted forwarding of packets during the failure of a router or a link in the network.

The main difference between OSPF NSR and OSPF NSF is their focus. NSR (Non-Stop Routing) is focused on preserving routing protocol state information across the failure of a router or a line card, while NSF (Non-Stop Forwarding) is focused on preserving packet forwarding information.

In NSR, the router that performs the switchover preserves the routing protocol state information internally. When a switchover occurs, the router continues forwarding packets without any disruption since it maintains the routing protocol state information. The benefit of NSR is that it reduces the downtime of the network and avoids the need for a full recalculation of the routing table.

On the other hand, with NSF, the newly active router in the case of a failover maintains the forwarding information. In other words, it maintains the adjacency with its neighbors and continues forwarding packets even after a failure. The key benefit of NSF is that it ensures the continuity of packet forwarding without any interruption, minimizing packet loss.

To summarize, NSR and NSF mechanisms provide complementary benefits in preserving routing protocol state and forwarding information across network failures. NSR focuses on preserving the routing protocol state, while NSF focuses on preserving the forwarding information.