MCP Server A wants data from Server B to complete a tool call. Using o — MCP Professional Practice — Claude Cert Academy

MCP Server A wants data from Server B to complete a tool call. Using only MCP protocol primitives, how can this be achieved?

• Server A calls Server B using MCP server-to-server RPC
• Server A requests a sampling call, which the model then uses to query Server B
• The host or client layer must orchestrate the cross-server data retrieval
• Server A and Server B share state through a common resource URI

Answer: The host or client layer must orchestrate the cross-server data retrieval

MCP has no server-to-server RPC primitive. Servers do not communicate with each other directly in the MCP protocol. Cross-server orchestration must happen at the host or client layer, which manages multiple client connections. Sampling allows the server to invoke an LLM, not another server.

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