CCNA Automation and Assurance Questions

In model-driven telemetry on Cisco XR, a subscription must explicitly associate a sensor-group (which defines the data to collect) with a destination-group (which defines where to send it). If these are not correctly associated and committed, the router will not stream any telemetry data to the collector, even if the collector is reachable. The verification of reachability confirms the network path is fine, so the next logical step is to check the subscription configuration.

B is correct because pyang is a YANG data modeling language validator and converter that can validate YANG modules against device capabilities (e.g., via RFC 7895 YANG Library) and generate Python bindings (e.g., using the `--plugindir` or `pyang --format pybind` options) for use in automation scripts. It directly supports the task of validating YANG models and producing Python code, unlike the other options which are protocols or automation frameworks.

Dial-out telemetry is the correct model because it allows the router to initiate a TCP connection to the collector, even when the collector is behind NAT and cannot be reached from the router. In dial-out mode, the router acts as the client and pushes telemetry data to the collector's configured IP address and port, bypassing the need for the collector to initiate the connection. This contrasts with dial-in models where the collector must reach the router, which is impossible when the collector is behind NAT.

Cisco NSO (Network Services Orchestrator) is a key technology for automated service provisioning because it provides a multi-vendor, service-oriented orchestration layer that uses YANG models and NETCONF to manage device configurations and service lifecycles. It enables operators to define services as templates, then push consistent configurations across the network, drastically reducing manual CLI-based provisioning.

The IP SLA UDP jitter operation completed successfully, meaning the destination is reachable and the operation is running. However, if the threshold is set too high, the IP SLA will not trigger a reaction (e.g., an SNMP trap or route change) even when jitter exceeds acceptable levels for voice quality. The customer reports voice quality issues, so the engineer must check if the jitter threshold is configured too high, masking the problem.

The `ios_config` module with `check_mode` (enabled via the `--check` flag or `check_mode: yes`) allows Ansible to first verify device reachability and then compare the intended configuration against the running configuration without making changes. Only when a difference is detected and `check_mode` is disabled will the module apply the configuration changes. This directly meets the requirement of applying configurations only when the device is reachable and the current configuration differs from the intended.

A 404 Not Found response to a RESTCONF PATCH request targeting a specific interface indicates that the resource (the interface) does not exist at the given URI. RESTCONF uses the URI path to identify the exact YANG data node; if the interface name in the URI does not match any configured interface on the Cisco ASR 9000, the server returns 404. This is consistent with RFC 8040, where 404 is used when the target resource cannot be found.

The gNMI ON_CHANGE subscription mode is designed to stream telemetry updates only when the value of a subscribed path changes. Since the NMS is missing BGP flap events, the subscription must be using SAMPLE mode, which periodically polls the state and can miss transient events between sampling intervals. Changing the subscription to ON_CHANGE ensures that every state transition (e.g., BGP session up/down) is immediately pushed to the collector, capturing all flaps.

Checking telemetry subscription statistics on each router (e.g., using show telemetry statistics) provides per-router counters for drops, errors, and sequence gaps. This directly identifies which routers are experiencing loss. Other options are either too manual, network-wide, or do not isolate individual routers.

The collector can establish a gRPC-TLS connection but receives empty data because the sensor-group path 'openconfig-interfaces' is not supported on the Cisco XR router. Cisco IOS XR supports OpenConfig paths only if the corresponding YANG models are loaded and the device implements those models; if the path is unsupported, the router will accept the subscription but send no telemetry data for that path. This is a common misconfiguration when using gRPC telemetry with OpenConfig models on platforms that may not fully support all OpenConfig paths.

Model-driven telemetry uses a push model where network devices continuously stream structured data (e.g., YANG-encoded) to a collector, eliminating the need for periodic SNMP polling. This provides real-time visibility with minimal CPU overhead on the device, as the device itself initiates the data export based on configured subscriptions, rather than responding to repeated GET requests.

PATCH is the appropriate HTTP method for a partial update to an existing resource, and the URI targets the IPv4 address list under the specific interface. This allows adding a new IPv4 address without replacing the entire interface configuration, which aligns with RESTCONF's support for partial resource modification as defined in RFC 8040.

NSO provides northbound APIs using NETCONF and RESTCONF, enabling integration with higher-level orchestration and management systems. These standard protocols allow external systems to interact with NSO for service lifecycle management, configuration, and operational data retrieval, making B correct.

On-change reporting with suppression reduces data rate by sending updates only when values change, and suppression prevents too-frequent updates. Increasing sample interval risks missing threshold events. Other options do not effectively reduce data rate while preserving event detection.

Using IETF YANG models (e.g., RFC 8299 for L3VPN) provides a vendor-neutral data model that both Cisco and Juniper support via NETCONF. Creating separate Jinja2 templates for each vendor ensures the generated XML conforms to each device's native YANG models, avoiding syntax errors. This approach maintains automation consistency while respecting vendor-specific implementations.

YANG (RFC 6020/7950) is a data modeling language specifically designed to model configuration and state data for network management protocols like NETCONF and RESTCONF. YANG defines the structure, constraints, and semantics of data that can be exchanged via these protocols, making it the standard for model-driven network automation.

The 'backup' option in the ios_config module instructs Ansible to save a copy of the running configuration to a local file before making any changes. If the playbook fails or produces an undesired state, the operator can restore the device to the previous configuration using that backup file. This provides a straightforward rollback mechanism for MPLS VPN deployments without requiring external version control or manual snapshots.

B is correct because PCEP with stateful delegation allows the SDN controller to compute and instantiate SR-TE tunnels dynamically, while the router delegates control to the controller for path updates. This approach ensures fast convergence by enabling the controller to react to network changes in real time and scales efficiently by centralizing path computation, avoiding per-router configuration overhead.

If the RESTCONF request path includes a specific interface key (e.g., /restconf/data/ietf-interfaces:interfaces/interface=GigabitEthernet0/0/0), the API will return only that single interface's operational data, even if the engineer intended to retrieve all interfaces. RESTCONF uses URI-encoded keys to filter resources; omitting the key returns the entire list, while including a key narrows the response to that specific instance.

In NSO, services are committed to push configuration changes to devices. If the commit is not performed, the changes remain in the candidate database and are not applied. Other options are less likely given the symptom.

NETCONF (RFC 6241) is the correct choice because it is designed specifically for network configuration management, supporting full datastore operations (e.g., <get-config>, <edit-config>, <copy-config>) and selective retrieval of configuration data using subtree or XPath filtering. This aligns directly with the engineer's requirement for both datastore operations and selective retrieval.

The Cisco IOS-XE native YANG model (urn:cisco:params:xml:ns:yang:cisco-native) structures BGP configuration under /native/router/bgp/scope/global/always-compare-med. The 'scope' container is required to differentiate between global and VRF-specific BGP settings, and 'always-compare-med' is a leaf within the global scope. This path accurately reflects the hierarchical model used by Cisco for BGP automation.

The <get> NETCONF operation retrieves both configuration and operational state data from a device, making it the correct choice for this requirement. Unlike <get-config>, which only returns configuration data, <get> accesses the running datastore and includes state data such as interface statistics, routing tables, and system status. This aligns with RFC 6241, where <get> is defined as the operation to retrieve combined config and state information.

When NSO deploys a service, it first checks whether the target devices are in sync with the NSO CDB (configuration database). If a device is out of sync (e.g., its running configuration differs from what NSO expects), NSO will refuse to push the new service configuration and will report a 'failed to reach devices' error, even though the device is reachable via SSH/NETCONF. This is a safety mechanism to prevent configuration conflicts or overwriting unmanaged changes.

The UDP Jitter operation (option E) is correct because it measures both one-way jitter and packet loss by sending UDP packets with precise timestamps, which is essential for diagnosing voice quality issues. Unlike other IP SLA operations, UDP Jitter specifically tracks inter-packet delay variation (jitter) and loss patterns that directly impact VoIP and real-time traffic.

The most likely cause is that the SSH host key of the router is not in the controller's known_hosts file. NETCONF over SSH (RFC 6242) requires SSH transport, and the controller must authenticate the router's SSH host key during session establishment. If the host key is missing or mismatched, the SSH handshake fails, preventing the NETCONF session from starting, even though the router is reachable and NETCONF is enabled.

The collection protocol (gRPC, gNMI, or native TCP) is critical because it determines the transport mechanism, security model, and compatibility with the telemetry collector. gRPC offers high-performance streaming with TLS, gNMI provides a standardized interface for both telemetry and configuration, and native TCP is simpler but less flexible. Choosing the wrong protocol can lead to interoperability issues or performance bottlenecks in a large SP network.

NETCONF uses TCP port 830 as its default transport port (per RFC 6242). If a firewall blocks this port, the TCP three-way handshake cannot complete, preventing the NETCONF session from establishing. This is a common network-layer cause of session failure.

Static routes require global config mode and must specify the destination network, subnet mask, and next-hop address or exit interface.

A load balancer distributes incoming gRPC streams from all 200 routers across multiple collectors based on a configured algorithm (e.g., round-robin or least connections), achieving even load distribution without per-router configuration. The routers simply send telemetry to a single virtual IP (VIP), and the load balancer forwards each stream to an available collector, preventing any single collector from being overwhelmed. This matches the requirement to offload processing and avoid manual configuration per router.

In IOS-XR telemetry, a destination-group must include the 'protocol' keyword (e.g., 'protocol grpc' or 'protocol tcp') to specify the transport protocol for the collector. Without this specification, the router does not know how to send the telemetry data, and the collector at 10.1.1.100 will not receive any data.

A 401 Unauthorized response indicates the request lacks proper authentication. The engineer likely forgot to include HTTP basic authentication headers with the correct username and password. Other options relate to content types or TLS, which would cause different errors (e.g., 415 Unsupported Media Type).

A 400 Bad Request in RESTCONF indicates a client-side error, typically malformed syntax. The most common cause is an invalid JSON payload, such as incorrect data types (e.g., string instead of integer) or missing mandatory leafs defined in the YANG module. RESTCONF validates the payload against the YANG schema before applying the configuration, and any schema violation triggers a 400 error.

Using a staging environment with identical configuration to test before production is the best practice because it allows validation of automation scripts and configuration changes in a controlled setting that mirrors the production network. This approach identifies potential errors, compatibility issues, or unintended side effects without risking service disruption, aligning with Cisco NSO's recommended deployment workflow that emphasizes pre-production testing to ensure change reliability.

These are essential multicast protocols for service provider IPTV and content delivery.

Cisco NSO provides a built-in transaction management system that automatically rolls back a service deployment to its previous state if any part of the deployment fails. This ensures service lifecycle integrity by preventing partial or inconsistent configurations across devices.

NETCONF hello message exchange includes the list of supported YANG modules in the capabilities. This is the standard way to discover device capabilities. Other options are either not standard or would not provide the required information.

Model-driven telemetry uses structured data models defined in YANG, which provides a standardized, hierarchical representation of device state and configuration. This contrasts with SNMP polling, which relies on flat MIB variables and often requires complex parsing of unstructured data. YANG models enable consistent data retrieval across multivendor environments and simplify automation workflows.

ON_CHANGE mode in gNMI ensures that the target device sends a telemetry update immediately whenever a state change occurs, guaranteeing that no updates are missed. This is in contrast to SAMPLE mode, which only sends periodic snapshots and can miss transient changes between intervals. Therefore, to capture all state changes, ON_CHANGE is the correct subscription mode.

YANG data models (C) are required because they define the structure and semantics of the telemetry data being streamed. gRPC uses YANG as its schema language to encode data in Protocol Buffers (protobuf) or JSON format, ensuring the receiver can parse and interpret the telemetry information correctly.