What is a significant disadvantage of using distance-vector protocols?

Using distance-vector protocols has a significant disadvantage in terms of their convergence times and susceptibility to routing loops. Distance-vector protocols operate on the principle of sharing knowledge about the entire network as it is learned from neighboring routers. Each router periodically sends out its entire routing table to its neighbors, which can lead to slow updates across the network as changes in topology are propagated.

This slow convergence can result in scenarios where routers may have inconsistent views of the network. For instance, if a route goes down, it takes time for that information to spread through the network, during which time other routers may continue to use the now-invalid route leading to routing loops. A routing loop occurs when packets circulate endlessly between routers without reaching their destination, which can cause network inefficiencies and increased latency.

Although distance-vector protocols are sometimes simpler in design, their vulnerability to slow convergence and routing loops makes them less suitable for large or rapidly changing networks compared to link-state protocols, which maintain a more up-to-date and accurate picture of the network topology.