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350-401 Practice Question: Is troubleshooting a model-driven telemetry…

A network engineer is troubleshooting a model-driven telemetry deployment on a Cisco IOS-XE router. The telemetry subscription is configured to stream interface statistics using gRPC dial-out to a collector at 10.1.1.100:50051. The engineer verifies that the collector is listening on the port and the router can reach it. However, the collector shows no data received. The engineer checks the router's telemetry logs and sees 'Connection refused' errors. What is the most likely cause?

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

The gRPC server on the collector is not running or is listening on a different port

That the collector is not configured to accept gRPC connections, or the gRPC server on the collector is not running. The 'Connection refused' error indicates that the TCP connection is being rejected, typically because the collector's gRPC server is not listening on that port. The other options are incorrect because the router can reach the collector, so firewall is not blocking; the subscription is configured correctly; and the encoding is not the cause of connection refusal.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • The collector's firewall is blocking the connection from the router

    Why it's wrong here

    If the firewall were blocking, the error would likely be 'No route to host' or timeout, not 'Connection refused'.

  • The gRPC server on the collector is not running or is listening on a different port

    Why this is correct

    'Connection refused' occurs when the TCP SYN reaches the host but no application is listening on the specified port.

  • The telemetry subscription is missing the 'encoding' configuration

    Why it's wrong here

    Missing encoding would not cause a connection refusal; the router would still attempt to connect.

  • The router's source-interface is not configured, causing the router to use an unreachable IP

    Why it's wrong here

    If the source IP were unreachable, the error would be 'No route to host' or timeout, not 'Connection refused'.

Visual reference

Client Server SYN (seq=100) SYN-ACK (seq=200, ack=101) ACK (ack=201) Connection established — data transfer begins

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Last reviewed: Jun 18, 2026

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