TCP, UDP and RFC 2217 debugging

TCP, UDP and RFC 2217 debugging

Serial-to-network modules and gateways often need both sides checked together.

• TCP Client: connect to a device, gateway or test server.
• TCP Server: listen locally and observe incoming clients.
• UDP: test datagram-based protocols, broadcast-like discovery or gateway forwarding.
• Hex mode: use it for binary payloads over TCP or UDP, not only for serial ports.
• Indicator lamps: a TCP/UDP connection keeps only the TX/RX activity pair; the six serial control-line lamps hide automatically.
• Tx counter: it only counts bytes the transport actually accepted. While a TCP server has no connected client, sending neither increases the Tx counter nor blinks the TX lamp — a quick way to tell whether data really left the application.
• Logs: save network-side traffic when comparing it with serial-side traffic.

When TCP or UDP fails, check IP address, port, firewall rules, subnet, gateway mode and whether another process already holds the same local port.

Use RFC 2217 with a serial bridge

RFC 2217 adds serial-port control to a Telnet-compatible TCP connection. Use it when the remote side must receive serial bytes and control the bridged serial port, rather than treating the link as a plain byte stream.

1. Create the serial endpoint and the TCP endpoint required by the topology.
2. Create the bridge, choose RFC 2217 instead of Transparent, and keep bidirectional forwarding enabled.
3. Connect with an RFC 2217-capable client or virtual COM-port tool. A plain TCP socket is not compatible with this mode.
4. From the remote client, request the required baud rate, data bits, parity, stop bits, DTR/RTS or Break state; the bridge applies the supported controls to its serial endpoint.
5. Verify both data directions and confirm the physical device is using the requested serial settings. Keep one controlling client at a time unless the complete workflow has been tested with multiple clients.

RFC 2217 does not provide encryption or authentication by itself. Restrict allowed clients and firewall access, or carry the connection through a trusted VPN or another protected network.