Automation and Assurance: model-driven programmability, telemetry, and verification
What this domain tests
Automation and Assurance tests model-driven programmability, streaming telemetry, and operational verification. Expect questions that distinguish YANG data models from protocols, compare SNMP polling with model-driven telemetry, and select the right assurance tool.
Core rules
- YANG models configuration and state data. It is not a transport protocol.
- NETCONF runs over SSH, commonly port 830, and uses XML. RESTCONF runs over HTTPS, commonly port 443, and uses JSON or XML. gNMI runs over gRPC and supports configuration and telemetry.
- Model-driven telemetry supports dial-out and dial-in subscriptions. Sample subscriptions send at an interval; on-change subscriptions send when a value changes.
- Assurance tools include SNMP polling, syslog, IP SLA probes, BFD, and streaming telemetry. BFD detects forwarding-path failures quickly; IP SLA measures reachability and performance with probes.
- BFD asynchronous mode has both sides send control packets; echo mode loops test packets through the neighbor.
Worked example
An operator needs interface operational state reported immediately when it changes, and interface counters every 10 seconds. A single SNMP polling interval is a poor fit for the state change because it only observes the value at poll time. Use a gNMI on-change subscription for the operational-state leaf so the router pushes a update when the value changes. Use a sample subscription with a 10-second interval for counters. If the collector is behind NAT and cannot reach the router, choose dial-out from the router to the collector rather than dial-in. Verify the YANG path and encoding before deployment; a wrong path returns an error even when gRPC connectivity is healthy.
Traps that cost marks
- Treating YANG as a protocol; NETCONF, RESTCONF, and gNMI carry modeled data.
- Using NETCONF over HTTP or assuming RESTCONF uses SSH.
- Choosing SNMP polling for fast state changes when on-change telemetry is required.
- Confusing BFD with IP SLA; BFD is a fast failure-detection protocol, IP SLA is a probe suite.
- Forgetting dial-out versus dial-in when the collector cannot initiate to the router.