Which communication protocol does DNP3 use by default?

DNP3, or Distributed Network Protocol version 3, is primarily used in the utility and automation industries for communications between control systems and field devices. By default, DNP3 operates in plaintext, meaning that the data exchanged between devices is not encrypted. This choice allows for ease of implementation and interoperability among a wide range of devices and systems.

Using plaintext can facilitate faster communication and lower overhead since there is no need for encryption and decryption processes. However, this also exposes the communication to potential security risks, which is why additional security measures, such as using DNP3 Secure Authentication or implementing secure network practices, are often recommended in modern applications to protect against unauthorized access or data tampering.

The other options, while relating to various security and networking practices, do not characterize the default operational mode of DNP3. Encrypted packet data and Secure Sockets Layer suggest secure communication methods, which are not the default for DNP3. Token Ring, meanwhile, refers to a specific network technology rather than a communication protocol used by DNP3. Thus, the correct identification of DNP3's default protocol as plaintext is essential for understanding the protocol’s operational characteristics and associated vulnerabilities.