200-901 Understanding and Using APIs Practice Question
In gNMI, what is the difference between dial-in and dial-out streaming?
⚠ Common exam trap
Cisco often tests the direction of connection initiation (client vs. device) as the key differentiator, and the trap here is confusing which side initiates the connection in dial-in versus dial-out, leading candidates to reverse the roles as in Option B.
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
✓
Dial-in: client initiates subscription and receives data; dial-out: device pushes data to a configured receiver
In gNMI, dial-in streaming refers to the client initiating a subscription request to the device, which then streams telemetry data back over the same gRPC session. Dial-out streaming, on the other hand, is a server-initiated model where the device (gNMI target) pushes telemetry data to a pre-configured receiver (collector) without waiting for a client request. Option C correctly captures this distinction: dial-in has the client subscribe and receive data, while dial-out has the device push data to a configured receiver.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Dial-in is for configuration, dial-out for telemetry
Why it's wrong here
Both dial-in and dial-out carry telemetry and can carry configuration via Set operations; the modes differ by connection initiator, not by data type. It is tempting because dial-out is commonly used for streaming telemetry, but dial-in also supports Subscribe for the same purpose.
- ✗
Dial-in: device initiates the connection; dial-out: client initiates
Why it's wrong here
The roles are reversed: in dial-in the client (collector) initiates the connection to the device, while in dial-out the device initiates the connection to the collector. It is tempting because 'dial-in' suggests the device dialling in, but the naming reflects the client's perspective.
- ✓
Dial-in: client initiates subscription and receives data; dial-out: device pushes data to a configured receiver
Why this is correct
Dial-in has the client open the gNMI session and subscribe, so the client receives streamed telemetry. Dial-out reverses this: the network device initiates the connection and pushes data to a preconfigured collector. The stem asks for this directional difference.
- ✗
Dial-in uses gRPC, dial-out uses HTTP
Why it's wrong here
Both dial-in and dial-out gNMI streaming use gRPC, not HTTP; the transport is identical. It is tempting because dial-out involves the device pushing telemetry, which superficially resembles HTTP-based push, but gNMI is defined exclusively over gRPC in both modes.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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