Free 300-535 Practice Test Questions and Answers (2026)

The output of the show telemetry ietf subscription 1011 detail command provides direct evidence for the cause of the issue. The State of the subscription is listed as Invalid, and the Notes field explicitly states, "The path is not supported". This indicates that the YANG sensor path Cisco-IOS-XR-infra-statsd-oper:infra-statistics/interfaces/interface/latest/generic-counters, which is part of the "Interface-Counters" sensor group, is either syntactically incorrect, not supported by the current IOS XR software version, or does not exist in the device's YANG data model. The router cannot create a valid subscription for a path it does not recognize.

A. A gRPC connection failure would be reflected in the subscription state as Connecting or Disconnected, or in the destination group status, not as Invalid with a path-related error note.
C. A subscription waiting for a collector in a dial-in model would not have an Invalid state. The state would typically be Idle or Connecting once a connection is attempted.
D. The expected state for a functioning, active subscription is Active. The Invalid state clearly indicates a configuration error, not normal operation.

1. Cisco IOS XR Model-Driven Telemetry Configuration Guide, Release 7.5.x

Section: Configure Model-Driven Telemetry > Verify Model-Driven Telemetry Configuration

Content: This guide details the output of the show telemetry ietf subscription command. It explains that the Invalid state indicates a configuration problem. The Notes field provides specific reasons for the failure, such as "The path is not supported," which directly correlates to an incorrect sensor-path configuration within the sensor-group.

2. Cisco IOS XR Programmability Configuration Guide, Release 7.3.x

Section: Implementing Model-Driven Telemetry > Verifying the MDT Configuration

Content: This document describes the various states of a telemetry subscription. An Invalid state is explicitly mentioned as a result of configuration errors, such as specifying a non-existent or unsupported sensor path. The troubleshooting section for this state directs the user to verify the configured sensor paths against the device's supported YANG models.

The NETCONF protocol provides a locking mechanism to ensure that only one client can modify a device's configuration at a time, preventing conflicts. The datastore contains the complete, active configuration currently operating on the network device. When a client needs to edit this live configuration directly (a capability indicated by :writable-running), it first sends a request for the datastore. This lock must be acquired before any operations can be safely performed, ensuring transactional integrity.

B. common: This is not a standard NETCONF datastore. The standard datastores are defined in RFC 6241 and do not include a "common" datastore.
C. startup: The datastore holds the configuration loaded on boot. It is typically locked when copying the running configuration to it, not during live configuration edits.
D. working: This is not a standard NETCONF datastore name. The datastore acts as a working or scratchpad area, but "working" is not a valid target. ---

1. RFC 6241 - Network Configuration Protocol (NETCONF):

Section 7.1, Operation: "The operation allows the client to lock the entire configuration datastore system of a device... The parameter specifies the configuration datastore to be locked." The example shows as a valid target.

Section 8.3.3.1, :writable-running Capability: "If a device advertises this capability, it supports writing to the datastore. A client can lock, edit, and unlock the datastore."

2. Cisco IOS XE Programmability Configuration Guide, Cisco IOS XE Bengaluru 17.6.x:

Chapter: NETCONF Protocol, Section: NETCONF Lock and Unlock Operations: "The NETCONF and protocol operations acquire and release a lock on a device's configuration... The lock is granted for the datastore that is specified in the operation, for example, the running datastore." This confirms that the running datastore is a primary target for locking during configuration management.

The provided Python script utilizes the ncclient library to send a NETCONF edit-config operation to a Cisco IOS XE device. The XML payload within the ospfconfig variable is structured according to the Cisco-IOS-XE-native YANG model. Analyzing the XML: 100 corresponds to router ospf 100. 1.1.1.1 corresponds to router-id 1.1.1.1. The block with 10.1.1.0, 0.0.0.3, and 0 corresponds to network 10.1.1.0 0.0.0.3 area 0.
Option A is the only choice that correctly and completely represents all configuration elements defined in the XML payload.

B. This option is incomplete as it omits the router-id 1.1.1.1 command, which is explicitly defined by the tag in the XML payload.
C. This option incorrectly swaps the values for the router-id and the network IP address, contradicting the values specified in the XML payload.
D. This option is incomplete as it omits the network 10.1.1.0 0.0.0.3 area 0 command, which is explicitly defined by the block in the XML.

1. Cisco IOS XE Programmability Configuration Guide, Release 17.x: In the "NETCONF Protocol" chapter, the guide explains how XML-encoded data based on YANG models is used in operations to manipulate the device's configuration. The structure in the question is a standard example of this process.

2. Cisco YANG Models GitHub Repository: The Cisco-IOS-XE-ospf.yang model file defines the data structure for OSPF configuration. The XML tags used in the script (id, router-id, network, ip, mask, area) directly correspond to the leaf and container definitions within this official YANG model, confirming the mapping to the CLI commands. (See vendor/cisco/xe/17.6/Cisco-IOS-XE-ospf.yang).

3. Cisco DevNet, "Introduction to Model-Driven Programmability" Learning Lab: This courseware provides practical examples of using ncclient to send NETCONF requests with XML payloads to configure IOS XE devices. The examples demonstrate the direct one-to-one mapping between the XML structure derived from a YANG model and the resulting CLI configuration.

Asynchronous API communication is a non-blocking method where a client sends a request to a server and does not wait for an immediate response to continue its processing. The client can proceed with other tasks while the server handles the request in the background. This approach is highly efficient for long-running operations, as it prevents the client application from being blocked or "frozen." The client can later poll for the result or receive a notification (e.g., via a webhook) once the task is complete. Therefore, it is not necessary for the client to wait for the resource to be available or for the operation to finish.

A. This statement describes synchronous communication, where the client sends a request and is blocked until a response is received.
B. The use of a central orchestrator is an architectural choice and is not a defining characteristic of synchronous or asynchronous communication.
D. An application freezing due to an unresponsive request is a characteristic problem of synchronous communication, which asynchronous patterns are designed to avoid. ---

1. Cisco NSO Documentation: In the Cisco NSO 6.0 Administration Guide, Chapter: "Transactions", Section: "Committing the Transaction", the documentation distinguishes between synchronous and asynchronous commits. It states, "When you commit asynchronously, the commit returns immediately... The commit operation continues in the background." This illustrates that the client does not wait.

2. Cisco DevNet Learning Labs: In the "Introduction to Webex APIs" module, Section: "Webhooks", it explains the asynchronous nature of webhooks: "Instead of your application polling the Webex API for changes... Webex will send your application an HTTP POST request... This is a much more efficient, 'asynchronous' method." This exemplifies a common asynchronous pattern where waiting is not required.

3. University Courseware: In materials for computer science courses on distributed systems, asynchronous communication is defined by its non-blocking nature. For instance, course notes often explain that in an asynchronous system, the sender of a message does not block to wait for a reply. This core principle is captured in the correct answer. (e.g., concepts taught in courses like MIT's 6.824 Distributed Systems).

The provided Ansible playbook uses the cisco.iosxr.iosxrbgp module, which is specifically designed to manage BGP configuration on Cisco IOS XR devices. The task details clearly define the configuration to be applied:
- BGP Autonomous System (AS) is set to 65000.
- Two BGP neighbors are configured: 192.168.1.1 and 192.168.2.1.
- Redistribution from OSPF process 1 into the BGP IPv4 unicast address family is configured. The state: merged parameter instructs Ansible to apply and merge this configuration with the existing configuration on the target IOS XR router, thus actively modifying its state.

B: The state: merged parameter explicitly applies configuration changes; the module is not read-only and actively modifies the router's configuration. C: The module cisco.iosxr.iosxrbgp is specific to the Cisco IOS XR operating system, not IOS XE. It is also not a check-mode-only module. D: The playbook targets a Cisco IOS XR router, not a generic "Cisco IOS" router, and the specified Autonomous System number is 65000, not 500. ---

1. Ansible Documentation for the cisco.iosxr.iosxrbgp module. The official documentation states that this module "Manages BGP configuration on Cisco IOS XR devices." It also defines the state parameter, where merged (the default) ensures "the provided configuration is merged into the existing device configuration." The examples provided in the documentation mirror the structure used in the question for configuring AS, neighbors, and redistribution.

Source: Ansible Documentation, cisco.iosxr.iosxrbgpmodule.

Reference: https://docs.ansible.com/ansible/latest/collections/cisco/iosxr/iosxrbgpmodule.html, see "Synopsis" and "Parameters -> state" sections.

2. Cisco DevNet Documentation, "Ansible for Cisco IOS XR". This official Cisco guide introduces the cisco.iosxr Ansible collection and its purpose. It describes how these modules are used to automate configuration tasks on IOS XR devices, confirming that modules like iosxrbgp are intended for active configuration management rather than read-only validation.

Source: Cisco Systems, Inc., Cisco DevNet.

Reference: https://developer.cisco.com/docs/ios-xr/#!ansible-for-cisco-ios-xr, see section "Using the Ansible Modules".

To deploy a service in NSO, the code must first be compiled. The standard procedure involves running make clean all in the package's src directory to generate the .fxs compiled schema files. Next, the package must be placed in a location where NSO looks for packages; among the options, $NCS_DIR/packages is the standard directory structure referenced (representing the NSO installation's package path). Once the files are in place, the administrator must Log in to the NSO CLI and issue the packages reload command to instruct NSO to load the new or updated code. Finally, the deployment is validated using show packages package oper-status, which confirms if the package is operationally "up". The command services reload is incorrect (it does not load package code), and $NCS_PACKAGES is not a standard NSO environment variable.

Cisco Network Services Orchestrator (NSO) 5.5 Development Guide, Chapter 2: "Developing NSO Services", Section: "Compiling the Package" and "Loading the Package". (Describes the make clean all workflow and reloading packages).

Cisco NSO 6.0 User Guide, Chapter: "Package Management", Section: "Managing Packages". (Confirming packages reload as the command to load changes).

Cisco NSO 5.4 CLI Reference Guide, Command: show packages package oper-status. (Verifies this command displays the operational status of loaded packages).

RESTCONF is a REST-like protocol that provides a programmatic interface for accessing data defined in YANG models. It operates over HTTP/HTTPS. The Python requests library is the standard for making HTTP requests, making it essential for communicating with a RESTCONF endpoint to retrieve information (e.g., using an HTTP GET method). The data returned from a RESTCONF API is typically encoded in JSON format. The built-in Python json library is used to parse this JSON-formatted response into a Python object (like a dictionary or list), allowing the script to easily process and utilize the retrieved device information.

A. PySNMP: This library is used for the SNMP protocol, which is a distinct and separate protocol from RESTCONF for network management.
C. ncclient: This is a client library specifically for the NETCONF protocol. While related to RESTCONF through YANG, NETCONF is a different protocol.
D. YANG: YANG is a data modeling language used to define the structure of data, not a Python library for executing API calls.

1. Cisco IOS XE Programmability Configuration Guide, Release 17.x: In the chapter on the RESTCONF Protocol, the "Sample Python Script to Retrieve the YANG Data Model" explicitly demonstrates the use of both the requests and json libraries. The script imports them (import requests, import json) to send an HTTP GET request and then parse the JSON response. (See section: RESTCONF Protocol > How to Configure RESTCONF Protocol > Sample Python Script to Retrieve the YANG Data Model).

2. Cisco DevNet - "Introduction to RESTCONF" Learning Lab: The Python code examples provided in this official Cisco training module consistently use the requests library to send API calls to the RESTCONF interface and the json library to handle the data payload. For instance, a typical GET request is shown as response = requests.get(apiurl, ...) and the response is processed with response.json(), which internally uses the json library. (See Cisco DevNet Learning Labs, Network Programmability Basics, Module 5: RESTCONF).

Netmiko is a multi-vendor Python library designed to simplify SSH connections to network devices. It is built as a high-level wrapper around the Paramiko library, which provides the underlying SSHv2 protocol implementation. Netmiko abstracts the complexities of Paramiko, handling device-specific prompts and peculiarities, making it the standard choice for automating interactions with network device CLIs via SSH in Python.

A. sshmiko: This is not a standard or recognized Python library in the network automation ecosystem.
B. paramiko.agent: This is a specific module within the Paramiko library for SSH agent handling, not a separate library built upon it.
C. libssh2: This is a C library that provides an alternative implementation of the SSH2 protocol; it is not based on Paramiko.

1. Cisco Press, 300-535 SPAUTO Official Cert Guide: Chapter 4, "Python Libraries for Network Automation," section "Netmiko," explicitly states, "Netmiko is a Python library that is built on top of Paramiko. It simplifies the process of connecting to network devices and executing commands."

2. Cisco DevNet Learning Labs: In the "Introduction to Python for Network Engineers" module, the section on "Popular Python Libraries for Network Automation" describes Netmiko's role and its relationship with Paramiko. It highlights that Netmiko uses Paramiko for the base SSH connectivity while adding multi-vendor support. (Reference: Cisco DevNet, Module: Python for Network Automation).

3. Netmiko Official Documentation: The main project documentation clarifies its architecture. The pyproject.toml file in the source code explicitly lists paramiko as a core dependency, confirming that Netmiko is built upon it. (Reference: Netmiko Source Repository, pyproject.toml, [tool.poetry.dependencies] section).

The provided YANG model defines a service named abcservice. The augment /ncs:services statement indicates that this service configuration is placed under the top-level /ncs:services container in the Cisco NSO data model. The path to a specific service instance is constructed by appending the service list name (abcservice) and its key value (CustomerA). The question asks for the path to a nested resource, the router ios-device. While the technically complete XPath is /ncs:services/abcservice/CustomerA/router/ios-device, option D is the only choice that correctly identifies the mandatory root path /ncs:services and the subsequent service hierarchy, making it the best answer among the options.

A. The root path /ncs:abcservice is incorrect. The abcservice list is defined under the /ncs:services container, not at the root level.
B. This option is missing the mandatory /ncs:services root container where all NSO service instances are stored.
C. The root container is /ncs:services (plural), not /ncs:service (singular). This makes the path invalid. ---

1. Cisco NSO 5.7 Development Guide, Chapter: Creating a Service, Section: The Service YANG Model. This guide explains that service models are augmented into the /services path. It states, "All services must be defined in a YANG module and augmented into /services." This confirms that any valid XPath for a service instance must begin with /ncs:services.

2. Cisco NSO 5.7 Programmability Guide, Chapter: The YANG Data Model, Section: The services Data Model. This document explicitly states, "The top-level container for all services is called services." This directly invalidates options A, B, and C which use an incorrect or incomplete root path.

3. RFC 7950 - The YANG 1.1 Data Modeling Language, Section 7.17: The "augment" Statement. The standard defines that an augment statement adds new schema nodes to a target node. In this case, the abcservice list is added to /ncs:services, dictating the beginning of the XPath.

gNMI (gRPC Network Management Interface) is a protocol for network management that uses the gRPC framework for transport. The gRPC messages themselves are defined and serialized using Protocol Buffers (protobuf). However, the actual configuration or telemetry data payload carried within these protobuf messages can be encoded in different formats. The gNMI specification explicitly defines support for payloads encoded as JSON (including JSONIETF for standards compliance and readability) and as binary protobuf (for high performance and efficiency). The context of moving away from NETCONF's XML encoding makes these modern, efficient alternatives the correct choice.

A. gNMI was developed as a modern alternative to NETCONF and does not use XML for its native message or payload encoding.
B. While the notification message structure is defined by protobuf, the standard gNMI payload encodings do not include XML.
E. The gNMI notification message itself is encoded using protobuf, not JSON. The message carries a payload that can be JSON encoded.

1. OpenConfig gnmi.proto Specification: The official gNMI protocol definition file explicitly lists the supported payload encoding formats within the TypedValue message definition.

Source: OpenConfig GitHub Repository, gnmi.proto file.

Reference: In the TypedValue message definition, the oneof value field includes bytes jsonval = 10;, bytes jsonietfval = 11;, and bytes protobytes = 13;, directly specifying support for JSON and Protobuf payloads.

Link: https://github.com/openconfig/gnmi/blob/master/proto/gnmi/gnmi.proto#L136

2. Cisco IOS XR Programmability Configuration Guide: Cisco's official documentation for implementing Model-Driven Telemetry (MDT) confirms the supported encoding formats for gNMI.

Source: Programmability Configuration Guide, Cisco IOS XR Release 7.3.x, Chapter: Configure Model-Driven Telemetry.

Reference: In the section "gRPC Network Management Interface (gNMI)," the documentation states, "gNMI supports data encoding in JSON, Protobuf, and JSONIETF formats." This directly validates the use of both JSON and Protobuf for payload encoding.

When configuring a dial-out telemetry destination group on a Cisco IOS XR device, you must define the essential parameters for the router to establish a session with the collector. This includes specifying where to send the data (destination IP address and port) and how to send it (the data encoding format, such as GPB or JSON, and the transport protocol, such as gRPC or TCP). These four parameters—destination IP address, destination port, encoding, and protocol—are the mandatory components for defining a destination group. Without them, the configuration is incomplete and will fail to apply.

A. The source IP/port are not configured in the destination group, and the sampling interval is defined in the sensor group or subscription.
B. The source IP address and source port are incorrect parameters for defining the telemetry collector (the destination).
C. The sensor path, which specifies the data to be streamed, is configured in a sensor group, not the destination group.

1. Cisco IOS XR Programmability Configuration Guide, Release 7.5.x, "Configure Model-Driven Telemetry" chapter, "Configure Destination Group" section. The configuration example clearly shows the mandatory parameters:

telemetry model-driven

destination-group

address-family ipv4 port

encoding

protocol

This demonstrates that destination address, port, encoding, and protocol are the required elements.

2. Telemetry Configuration Guide for Cisco ASR 9000 Series Routers, IOS XR Release 6.6.x, "Configure Model-Driven Telemetry" chapter, "Configure a Destination Group for the Subscription" section. This guide provides a similar configuration example, reinforcing the same set of mandatory parameters for establishing a destination group for gRPC. The example explicitly configures an IPv4 address, port, encoding, and the gRPC protocol.

When creating a service package in Cisco NSO using the ncs-make-package --service-skeleton template command, a basic file structure is generated. To make this a functional service, the developer must perform two primary tasks. First, the service model must be defined in the generated YANG file (.yang). This model specifies the service's parameters that a user will configure. Second, the logic for mapping these service parameters to actual device configurations must be created in the XML template file (.xml). These two files contain the core logic of the service.

B. Modify the VLAN FastMap algorithm. FastMap is the internal NSO engine that processes service mappings; developers provide input to it via templates or code, but do not modify the algorithm itself.
C. Start the VLAN Python VM. The service skeleton was created using the template option, which relies on XML for mapping logic, not Python. A Python Virtual Machine is only relevant for Python-based services.
E. Compile the VLAN NED. Network Element Drivers (NEDs) are for device-level communication, not service logic. While a service uses NEDs, compiling a "VLAN NED" is not part of creating the service package itself.

1. Cisco NSO 5.7 Services Documentation, "Template-Based Service Packages" section. This guide details the workflow for creating a template-based service, explicitly stating the need to edit the YANG data model and the XML template file after generating the skeleton. The steps outlined are: 1. Create the package skeleton. 2. Edit the YANG data model file. 3. Edit the XML template file. 4. Compile and reload packages.

2. Cisco NSO 5.x Programmability and Automation Learning Labs (DevNet), "NSO Services" module. The lab exercises demonstrate the creation of a service package, which involves defining the service inputs in a YANG file and then creating the device configuration mapping in an XML template file. This reinforces that these are the essential development steps.

Cisco WAN Automation Engine (WAE) is a powerful software tool designed for network planning, modeling, and optimization. One of its primary functions is to perform what-if analysis, allowing network operators to simulate the impact of changes—such as link failures, traffic growth, or new service rollouts—before implementing them in the live network. Additionally, WAE is designed to work within a broader automation architecture. It integrates with Cisco Crosswork Traffic Controller (XTC), which acts as a Segment Routing Path Computation Element (SR-PCE). WAE performs complex, offline traffic engineering computations and provides optimized SR policies to XTC, which then deploys and manages them in the network.

A. WAE is used to plan and optimize SR policies, but the actual deployment is executed by a network controller like Cisco NSO or XTC, not by WAE itself.
D. WAE operates at the network-wide modeling and analytics level, not as a device manager responsible for individual element configuration, inventory, or lifecycle management.
E. WAE is an offline planning and optimization engine that provides intelligence to a network controller; it does not function as the real-time network controller itself.

1. Cisco WAN Automation Engine 7.3 Data Sheet:

For option C: Under the "Benefits" section, it explicitly states a key benefit is to "Perform 'what-if' analysis to understand the impact of network changes before they are made."

For option B: Under the "Cisco WAE components" section, it details the "WAE SR-PCE Integration" feature, stating, "The WAE SR-PCE Integration feature enables WAE to communicate with the Cisco Crosswork Traffic Controller (XTC), formerly known as Segment Routing Path Computation Element (SR-PCE)."

2. Cisco WAN Automation Engine Planning 7.3 User Guide:

For option C: In Chapter 1, "Introduction to WAE Design," the document states, "WAE Design is a tool for planning, simulating, and analyzing your network. You can model network behavior, assess the impact of changes, and optimize your network for maximum efficiency." This directly supports the "what-if analysis" use case.

For option B: Chapter 20, "SR-TE PCE," is dedicated to the integration with the Segment Routing Path Computation Element (now XTC), describing how WAE can read SR policies from the PCE and provision them back after optimization.

Assume the code defines b = 22 and d = 44, and swap1 is written as

def swap1(x, y): x, y = y, x return (x, y)

Calling swap1 therefore returns the two arguments in reverse order. To obtain the tuple (44, 22), we must give swap1 the values in the opposite order—first 22 (b), then 44 (d). print(swap1(b, d)) consequently prints (44, 22).

A. swap1(d, b) returns (22, 44) because the arguments are reversed inside the function.
B. swap2(a, b) acts on different variables; even if swap2 swaps, it involves a and b, not d.
D. swap2(22, 44) passes immutable ints; an in-place swap (likely using list indexing) cannot occur, raising an error.

1. Python Software Foundation. “The Python Language Reference – Assignment Statements,” Python 3.11 docs, §6.2.1 (explains tuple-unpacking swap).

https://docs.python.org/3/reference/simplestmts.html#assignment-statements

2. Python Software Foundation. “Data Model – Immutable Sequence Types,” Python 3.11 docs, §4.6 (ints are immutable, making in-place swap impossible).

https://docs.python.org/3/reference/datamodel.html#immutable-sequence-types

A container node in a YANG data model is an interior node designed to group related data nodes. According to the official YANG specification (RFC 7950), a container is defined as an interior data node that can exist at most once within its parent in the data tree. It does not hold a value itself; its sole purpose is to contain a set of child nodes, which can be other containers, leaves, lists, or any other YANG node type. This definition perfectly matches all criteria specified in the question.

A. listing node: This is not a standard term in the YANG data modeling language. The correct term is list, which can have multiple instances, violating the "at most one instance" rule.
B. tree node: This is a generic term for any node within a data tree and is not a specific type of YANG data node like container or leaf.
D. leaf node: A leaf node is a terminal node, not an interior one, as it cannot have child nodes. Furthermore, a leaf node is specifically defined to hold a value.

1. RFC 7950: The YANG 1.1 Data Modeling Language.

Section 4.2.3, "Container": "A container node is an interior data node that exists in at most one instance in the data tree. A container has no value, but it has a list of child nodes." This directly supports the correct answer.

Section 4.2.4, "Leaf": "A leaf node is a data node that exists in at most one instance in the data tree. A leaf has a value but no child nodes." This confirms why option D is incorrect.

Section 4.2.5, "List": "A list is an interior data node that may exist in multiple instances in the data tree." This confirms why the concept of a list (incorrectly termed "listing node") is wrong.

2. Cisco Systems, "YANG Data Models", Programmability Configuration Guide, Cisco IOS XE Bengaluru 17.6.x.

Chapter: YANG Data Models, Section: YANG Data Model Structure: This guide explains the basic building blocks of YANG. It describes a container as a node that "groups related nodes in a subtree" and a leaf as a node that "has a value and no child nodes," reinforcing the definitions from RFC 7950.