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Transport errors
Last update:
May 18, 2026
Transport errors occur when a client cannot establish or maintain a connection to the MCP server before the MCP protocol is successfully used.
Overview
Transport errors indicate failures at the communication layer. These errors occur before any MCP protocol-level interaction can take place and typically prevent the client from successfully connecting to or communicating with the MCP server.
Typical causes
- MCP server not reachable (incorrect URL, DNS failure, firewall restrictions, or service not running)
- TLS or SSL handshake failures
- Proxy or gateway errors
- Broken TCP connection while streaming responses (SSE)
- STDIO process cannot be started (incorrect binary path or missing permissions)
How transport errors surface
For HTTP or SSE transports:
- Connection refused or host not found errors
- HTTP 5xx responses from load balancers or gateways
- TLS certificate validation errors
For STDIO transports:
- Process spawn errors
- Non-zero exit codes immediately after process startup
- No data written to stdout or immediate end-of-file (EOF)
Recommended response
- Verify the URL, authentication token, and required headers in the MCP transport configuration.
- Ensure that the MCP server is running and reachable from the ColdFusion host.
- For STDIO transports, confirm that the command, arguments, and environment variables are correct and executable by the ColdFusion runtime.
- Implement retry with exponential backoff only for transient failures (such as temporary gateway errors), not for persistent configuration issues.
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