Which BGP feature enhances routing efficiency?

The feature that enhances routing efficiency in BGP is the implementation of rich routing policies. These policies allow network administrators to define specific rules for how routes are advertised and accepted based on various criteria such as prefix length, AS path, or community attributes. By using rich routing policies, BGP can optimize the selection and propagation of routes, ensuring that only the most efficient and suitable paths are chosen for data transmission. This leads to a more effective utilization of network resources and improved overall performance of the routing process.

In contrast, the other features, while important for BGP operation, do not directly contribute to routing efficiency. Automatic neighbor discovery simplifies the process of establishing BGP peering sessions, therefore aiding in BGP configuration but not necessarily improving routing efficiency. Plaintext authentication secures BGP sessions from unauthorized access, ensuring reliability but not addressing how routes are managed or optimized. Similarly, a reliable transport protocol ensures that BGP messages are delivered accurately and in order, which is crucial for stability but does not enhance the efficiency of routing decisions themselves.