Which code in a routing table indicates a route learned through a dynamic routing protocol?

In a routing table, the code 'D' denotes routes that have been learned through a dynamic routing protocol, specifically the EIGRP (Enhanced Interior Gateway Routing Protocol). Dynamic routing protocols automatically share routing information between routers, allowing them to adjust to changes in the network without manual intervention. This adaptability is crucial for maintaining an efficient network, particularly in environments where topology frequently changes.

The letter 'D' in the routing table signals to the network administrator that the route was not entered manually, but rather discovered by the router through exchanges with neighboring devices that also use EIGRP. This is a critical aspect of modern networking where dynamic routes can be preferred over static ones because they can provide more up-to-date and resilient routing paths as network conditions evolve.

In contrast, the other codes in the routing table represent routes learned through different means, such as 'C' for connected routes (for interfaces that are directly connected), 'S' for static routes (manually configured by an administrator), and 'R' for routes learned via the RIPv1 or RIPv2 protocols (which are also dynamic but specifically indicate a different protocol than EIGRP). Understanding these codes allows for effective interpretation of routing tables and better network management.