easyMultiple Choice
350-401 Practice Question: Is deploying streaming telemetry from a Cisco ASR…
A network engineer is deploying streaming telemetry from a Cisco ASR 1000 router to a collector using gRPC. The engineer notices that the telemetry data is not being received by the collector. The router shows that the gRPC server is running and the collector is reachable. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the distinction between the transport protocol (gRPC) being operational and the telemetry subscription being configured, trapping candidates who assume a running gRPC server implies telemetry data is flowing.
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
✓
No telemetry subscription is configured on the router for the desired data paths.
The gRPC server running and the collector being reachable indicates the transport layer is functional. However, streaming telemetry requires an explicit subscription configuration on the router that defines which data paths (e.g., YANG paths) to stream and to which collector. Without a subscription, the router has no instruction to send telemetry data, even if the gRPC server is active and network connectivity exists.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
No telemetry subscription is configured on the router for the desired data paths.
Why this is correct
In model-driven telemetry, a subscription is a required configuration construct that binds the desired YANG data paths (e.g., interfaces, CPU/memory stats) to a destination collector. Even if the gRPC server is operational and the collector is reachable, no telemetry data is streamed until a subscription is created and active on the router. This is the root cause because the symptom is a complete absence of data, not malformed or dropped data.
- ✗
The gRPC server is configured with the wrong port number.
Why it's wrong here
The gRPC server being configured with the wrong port would prevent the collector from establishing a connection or receiving any data, but the scenario states the server is running, which implies the port is correctly configured. In practice, if the port were wrong, the collector would see connection failures or nothing at all distinct from a subscription problem. Since the server is up, this option cannot explain the issue.
- ✗
The collector is not listening on the same IP address as configured on the router.
Why it's wrong here
If the collector were listening on a different IP than configured on the router, the router would send telemetry packets to an unresponsive address, resulting in no data delivery. However, the scenario explicitly states the collector is reachable, meaning the IP address matches and packets are successfully delivered. A reachable collector rules out IP address mismatch as the cause of zero data flow.
- ✗
The telemetry data is encoded in GPB, but the collector expects JSON.
Why it's wrong here
Encoding format mismatch (GPB vs JSON) would not prevent telemetry data from being sent; it would only cause the collector to fail when parsing or decoding the received messages. The symptom here is that no data is sent at all, which points to a pre-streaming failure like a missing subscription. Thus, an encoding mismatch is a plausible parsing problem but not the reason for complete absence of telemetry traffic.
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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