Routing And Switching Questions
The DUAL algorithm, which stands for Diffusing Update Algorithm, is a routing algorithm used in Cisco's Enhanced Interior Gateway Routing Protocol (EIGRP). It is responsible for calculating the best path to a destination network and maintaining loop-free routing in a network.
The DUAL algorithm works by maintaining three tables: the routing table, the neighbor table, and the topology table. The routing table contains the best path to each destination network, the neighbor table keeps track of neighboring routers, and the topology table stores information about the network topology.
When a change occurs in the network, such as a link failure or a new route becoming available, the DUAL algorithm is triggered. It uses a diffusing computation process to calculate the new best path to the affected destination network. This process involves exchanging information with neighboring routers and updating the topology table.
The DUAL algorithm uses several metrics, including bandwidth, delay, reliability, and load, to determine the best path. It assigns a composite metric to each path and selects the path with the lowest metric as the best path. If multiple paths have the same metric, load balancing can be achieved by using multiple paths simultaneously.
One of the key features of the DUAL algorithm is its ability to provide fast convergence. It achieves this by maintaining backup routes in the routing table, allowing for quick switchover to an alternate path in case of a primary path failure. This backup path is precomputed and readily available, reducing the convergence time.
Overall, the DUAL algorithm plays a crucial role in EIGRP by ensuring efficient and loop-free routing in a network, while also providing fast convergence and load balancing capabilities.