Which protocol is commonly used for routing in large networks?

The correct answer is OSPF, which stands for Open Shortest Path First. This protocol is widely used for routing in large networks due to its efficiency and scalability. OSPF operates using a link-state routing algorithm, allowing routers within an autonomous system to maintain a topology map of the entire network. This enables OSPF to quickly adapt to changes in the network, such as router failures or changes in link status, and efficiently compute the best paths for data packets using Dijkstra's Shortest Path First (SPF) algorithm.

OSPF is designed to handle large and complex network architectures, making it particularly suitable for enterprise environments where thousands of routers may be involved. Additionally, it supports hierarchical network design through the use of areas, which helps to reduce the size of routing tables and optimizes protocol performance.

In contrast, other options are not primarily used for routing in large networks. RIP (Routing Information Protocol) is a distance-vector protocol that works well in smaller networks but has limitations regarding scalability and convergence speed compared to OSPF. FTP (File Transfer Protocol) is used for transferring files over a network and does not facilitate routing. Telnet is a network protocol used for remote communication with devices, not for routing purposes.