Explanation/Reference:
Section: Addressing and Routing Protocols in an Existing Network Explanation Explanation:
Of the available choices, Enhanced Interior Gateway Routing Protocol (EIGRP) and redundant equal-cost paths to the destination are most likely to result in fast and deterministic recovery when a path to a destination becomes invalid. Both Open Shortest Path First (OSPF) and the Cisco-developed EIGRP are dynamic routing protocols and are capable of fast convergence. However, on a network that contains only Cisco routers, EIGRP is typically simpler to deploy than OSPF and can converge faster than OSPF because of the feasible successors stored in the EIGRP topology database.
One means of optimizing a routing design is to create redundant equal-cost paths between devices because such a design promotes fast and deterministic recovery when a path becomes invalid. When either EIGRP or OSPF has a redundant equal-cost path to a destination, all of the new path calculation occurs on the local device if one of the paths becomes unavailable. If the device has no redundant equal- cost paths, the routing protocol must rely on information from neighboring devices and calculate a new path.
Routing Information Protocol (RIP) does not offer fast recovery. RIP sends out routing updates every 30 seconds, so convergence is relatively slow. In addition, RIP relies on hold-down timers, which further slowdown convergence time.
The amount of time required for a routing protocol to detect the loss of a forwarding path and to calculate a new best path can both affect convergence time. In addition, the amount of time it takes for the Cisco Express Forwarding (CEF) table to populate with routing updates can affect the speed of convergence. It is therefore important when designing a network to ensure that the routing design is an optimized design.
Reference:
Cisco: High Availability Campus Network Design-Routed Access Layer using EIGRP or OSPF: Route Convergence