On Cisco iOS devices, which IS-IS feature reduces the convergence time for prefixes designated as high priority?
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A. B. C. D.A.
References:
The correct answer is C. iSPF (Incremental Shortest Path First).
IS-IS (Intermediate System to Intermediate System) is a link-state routing protocol used in many large-scale enterprise and service provider networks. IS-IS uses Dijkstra's shortest path first algorithm to calculate the shortest path from a source router to all destinations in the network.
In IS-IS, the convergence time is the amount of time it takes for all routers in the network to update their routing tables after a change occurs in the network topology. Convergence time is a critical factor in network performance and availability, especially in service provider networks.
IS-IS provides several features to reduce convergence time, including:
A. Route tagging: This feature is used to tag specific routes with a high priority. When a change occurs in the network topology that affects a tagged route, IS-IS gives the route priority in the SPF calculation to ensure that it is updated quickly. However, route tagging is not specifically designed to reduce convergence time.
B. Advertise passive only: This feature is used to prevent a router from advertising routes for interfaces that are in the passive state. This reduces the number of unnecessary route advertisements in the network, but it does not reduce convergence time.
C. iSPF: iSPF is a feature that incrementally updates the routing tables of routers in the network when a change occurs. Instead of recalculating the entire SPF tree, iSPF only recalculates the parts of the tree that are affected by the change. This significantly reduces the convergence time for the network, especially for high-priority prefixes.
D. Fast-Flooding: Fast-Flooding is a feature that is used to quickly flood topology changes throughout the network. When a topology change occurs, routers in the network can quickly update their routing tables to reflect the change, reducing convergence time. However, Fast-Flooding is not specifically designed to reduce convergence time for high-priority prefixes.
In summary, the correct answer to the question is C. iSPF, which is specifically designed to reduce convergence time for high-priority prefixes.