What remote operation allows a client to send its XML-formatted message to the server in NETCONF?

In the context of NETCONF (Network Configuration Protocol), the remote operation that allows a client to send an XML-formatted message to the server is called an RPC, which stands for Remote Procedure Call.

An RPC in NETCONF enables clients to execute commands on a remote server as if they were executed locally. This method supports the structured and defined interactions necessary for managing network devices programmatically. When a client issues an RPC, it constructs an XML message that encapsulates the request for a specific operation, such as retrieving configuration data or making changes to device settings. The server then processes this call and sends back a response, typically in XML format as well.

The other choices—request, message, and command—do not specifically capture the formal structure and nature of how NETCONF handles operations. While each of these terms may relate to aspects of communication or interaction, only RPC accurately describes the standard operational model that NETCONF utilizes for remote interactions between clients and servers.