JNCIA-DevOps Practice Test 3 — 30 Questions

Question 1

When writing a Python script that connects to multiple Junos devices concurrently using PyEZ, which Python module is commonly used to manage thread pooling and parallel execution?

Accepted Answer

concurrent.futures. The concurrent.futures module is the standard Python library for managing thread pools and parallel execution. It provides ThreadPoolExecutor and ProcessPoolExecutor, which are commonly used with PyEZ to connect to multiple Junos devices concurrently. This is the recommended approach for parallel device operations in Python scripts.

Answer

jnpr.junos.parallel

Answer

multiprocessing.device

Answer

asyncio.netconf

Question 2

In a DevOps pipeline managing Junos devices, an engineer implements 'Infrastructure as Code' (IaC). Which practice best exemplifies this methodology when applied to Junos routing policies?

Accepted Answer

Defining routing policies in Jinja2 templates and YAML data files, committing them to Git, and automatically pushing them via Ansible playbooks.. IaC defines infrastructure in declarative configuration files stored in version control, allowing automated testing and deployment.

Answer

Writing custom Python scripts that use regex to parse 'show route' outputs on the fly.

Answer

Manually logging into each router via SSH during a maintenance window to type out policy-options statements.

Answer

Using dynamic routing protocols like BGP to automatically advertise prefixes without human intervention.

Question 3

An engineer needs to explain the primary advantage of treating network configurations as code in a modern DevOps workflow. Which principle best describes this approach?

Accepted Answer

Storing configurations in a version control system to track history, enable rollbacks, and facilitate collaboration.. Treating network configurations as code allows infrastructure to be version-controlled, repeatedly deployed, and tested just like software code.

Answer

Immutable infrastructure deployment where devices are replaced rather than updated manually.

Answer

Compiling the network CLI commands into binary machine code before executing them on Junos devices.

Answer

Automating the complete removal of the command-line interface in favor of graphical topology builders.

Question 4

When writing a Python script to interact with Junos devices, you want to ensure that password credentials are not hardcoded in the source code. What is a recommended best practice supported by PyEZ?

Accepted Answer

Using SSH key-based authentication or environment variables/config files (.junodes). PyEZ natively supports configuration files like ~/.junodes or passing parameters dynamically, but also respects environment variables or SSH keys.

Answer

Disabling authentication in the script

Answer

Storing credentials in plaintext in a public GitHub repository

Answer

Hardcoding credentials in base64 encoding

Question 5

You send an edit-config RPC with an invalid XML tag name. What is the standard structure of the error returned in the <rpc-reply>?

Accepted Answer

An element containing diagnostic sub-elements like and .. NETCONF errors are returned inside an element containing details such as error-type, error-tag, and error-message.

Answer

A standard Linux kernel panic log string.

Answer

An HTTP 400 Bad Request status code.

Answer

A syslog message printed directly to the terminal emulator.

Question 6

Which TWO statements are true regarding the NETCONF protocol hello message exchange? (Choose two.)

Accepted Answer

Both client and server exchange capabilities using XML elements containing URI strings.. Option C is correct because in the NETCONF hello exchange both peers send a element containing a list, where each capability is expressed as a URI string (for example urn:ietf:params:netconf:base:1.0 or urn:ietf:params:netconf:capability:candidate:1.0), allowing each side to learn the other's supported features. Option D is correct because the server's hello includes a element, a positive integer attribute that uniquely identifies the NETCONF session for the duration of that connection. Option A is wrong because database locking is performed later with operations, not during the hello exchange, and the hello occurs before any configuration operations. Option B is wrong because the client hello advertises supported capabilities, not a list of YANG modules it intends to modify. Option E is wrong because the hello exchange is mandatory in NETCONF regardless of the SSH authentication method used.

Answer

The client uses the hello message to lock the configuration database before session initialization.

Answer

The client hello message must include the list of YANG modules it intends to modify during the session.

Answer

The hello message exchange is optional if a pre-shared SSH key is used for authentication.

Question 7

An automation engineer is writing a Python script that uses the ncclient library to connect to a Junos device via NETCONF. The engineer wants to retrieve the entire candidate configuration from the device. Which NETCONF operation should be used?

Accepted Answer

with source set to . To retrieve the candidate configuration via NETCONF, the correct operation is with the source datastore specified as . This operation reads configuration data from the chosen datastore. Other operations like target running state and configuration, modifies datastores, and changes configuration. Therefore, is the proper choice.

Answer

<get> with a subtree filter for configuration

Answer

<copy-config> from running to candidate

Answer

<edit-config> with operation 'get'

Question 8

In a Junos automation environment, what role does a schema (such as YANG or Junos XSD) play when interacting with NETCONF?

Accepted Answer

It defines the structural rules, data types, and valid hierarchy for configuration and operational data models.. YANG or XSD schemas define the data model structure, types, and constraints for configuration and operational data.

Answer

It encrypts the communication channel between the client and the Junos device.

Answer

It acts as a firewall filter blocking unauthorized IP addresses on the management interface.

Answer

It compiles Python scripts into executable machine code for the Routing Engine CPU.

Question 9

An automation engineer stores Junos interface descriptions in a YAML file. One description includes the text 'Link: 10G uplink to core-sw-01'. After loading the file with a standard YAML parser, the engineer finds the value is not parsed as expected. Which YAML syntax should the engineer use to store this value correctly?

Accepted Answer

Wrap the value in double quotes: "Link: 10G uplink to core-sw-01". YAML plain scalars cannot contain a colon followed by a space because that sequence signals a mapping key-value separator. Quoting the scalar with double quotes (or single quotes) tells the parser to treat the entire content as a literal string. This preserves the description exactly as intended so Junos configuration templates receive the correct value.

Answer

Prefix the value with an ampersand: &Link: 10G uplink to core-sw-01

Answer

Enclose the value in square brackets: [Link: 10G uplink to core-sw-01]

Answer

Escape the colon with a backslash: Link\: 10G uplink to core-sw-01

Question 10

You are writing a script that uses Jinja2 to dynamically render a Junos interface configuration. Which Python module and function are required to load a template from the local filesystem and render it with a dictionary of variables?

Accepted Answer

from jinja2 import Environment, FileSystemLoader. The standard Jinja2 API for loading templates from disk is to create an Environment with a FileSystemLoader pointed at the template directory, then call get_template() and render() with a variable dictionary. This is the canonical Python Jinja2 pattern and works directly with Junos config templates. PyEZ does not provide its own Jinja2 wrapper module for this purpose.

Answer

from jnpr.junos.cfg import ConfigTemplate

Answer

from jnpr.junos.template import TemplateRenderer

Answer

import jnpr.junos.utils.jinja as jinja

Question 11

When designing a version control workflow for Junos configurations using Git, which THREE practices are considered industry best standards? (Choose three)

Accepted Answer

Using feature branches for developing new configuration changes before merging into main. Option B is correct because feature branches isolate new Junos configuration changes from the main branch, allowing development and validation without destabilizing production-ready configurations before a controlled merge. Option D is correct because peer reviews and pull request approvals enforce a four-eyes principle, catching errors, policy violations, or unintended commit/rollback commands before changes reach the main branch. Option E is correct because semantic or descriptive commit messages document the intent of each configuration update, which is essential for audit trails, troubleshooting, and correlating commits with change tickets in Junos automation workflows. Option A does not belong because bypassing automated testing removes validation of syntax, commit checks, and rollback safety, increasing outage risk. Option C does not belong because storing plaintext administrative passwords in public Git repositories exposes credentials and violates security best practices; secrets should be managed with tools like Ansible Vault, HashiCorp Vault, or Junos encrypted passwords.

Answer

Completely bypassing automated testing to speed up deployments

Answer

Storing plaintext administrative passwords directly in public Git repositories

Question 12

In Git version control, which TWO commands are used to integrate changes from one branch into another? (Choose two)

Accepted Answer

git merge. git merge (B) is correct because it integrates changes from one branch into another by combining their commit histories, typically creating a merge commit when the target branch has diverged. git rebase (E) is also correct because it integrates changes by replaying commits from one branch onto another, producing a linear history. git init (A) only initializes a new repository and does not integrate branch changes. git status (C) merely reports working tree and staging state without modifying history. git clone (D) copies a remote repository locally but does not merge or rebase branches.

Answer

git init

Answer

git status

Answer

git clone

Question 13

A Python script retrieves interface statistics from a Junos device in JSON format, modifies a threshold value, and needs to output it back into a formatted JSON string with an indentation level of 4 spaces for readability. Which Python snippet achieves this?

Accepted Answer

json.dumps(data, indent=4). The json.dumps() method accepts an 'indent' parameter which specifies the number of spaces to use for pretty-printing the resulting JSON string.

Answer

json.format(data, spacing=4)

Answer

json.dump(data, indent=4)

Answer

json.stringify(data, spaces=4)

Question 14

Which of the following characters is used to start a comment line in a YAML document?

Accepted Answer

Hash sign (#). Comments in YAML begin with the hash or pound sign (#) and continue to the end of the line.

Answer

Exclamation mark (!)

Answer

Percent sign (%)

Answer

Double forward slash (//)

Question 15

You are writing a Python automation script that processes JSON output from a Junos device's 'show interfaces' operational command via PyEZ. One of the interface descriptions contains raw control characters. When the script attempts to dump this data to a JSON string using json.dumps(), it raises a ValueError. Which parameter should you pass to json.dumps() to handle non-printable or out-of-range character encoding gracefully?

Accepted Answer

ensure_ascii=False. The json.dumps() function in Python includes an 'ensure_ascii' parameter. When set to False, it allows non-ASCII characters to be emitted directly without raising serialization errors or escaping them into Unicode escape sequences.

Answer

skipkeys=True

Answer

check_circular=False

Answer

allow_nan=True

Question 16

A network engineer writes a Python script using Junos PyEZ to push a configuration change. The script uses the ConfigTable or Config class. What mechanism does PyEZ use under the hood to ensure the configuration lock is released even if the script encounters an unhandled exception?

Accepted Answer

Python context managers ('with' statements) that automatically release locks and clean up session state upon exit.. Python context managers (using the 'with' statement) automatically handle acquiring and releasing locks and rolling back candidate changes on exception in PyEZ.

Answer

NETCONF keepalive timers that drop the SSH session after 1 second.

Answer

A UNIX cron job that reboots the router every 5 minutes.

Answer

Hardware watchdog timers built into the Routing Engine ASIC.

Question 17

When managing Junos configuration changes in a team environment, why is atomic configuration rollback capability crucial during automated deployments?

Accepted Answer

It ensures that either all configuration statements in a transaction are applied successfully or none are, preventing partial/corrupt states.. Atomic rollbacks ensure that if a change set fails validation or causes a network fault, the system can revert cleanly to the previous working state without partial application.

Answer

It compresses the configuration database to save NVRAM storage space.

Answer

It allows the router to dynamically rewrite Python scripts into C++ for faster execution.

Answer

It automatically backs up the entire Junos OS image to an external TFTP server.

Question 18

Which NETCONF RPC tag is used to gracefully terminate an active NETCONF session with a Junos device?

Accepted Answer

. The RPC requests graceful termination of the NETCONF session.

Answer

<terminate-session>

Answer

Answer

<kill-session>

Question 19

What is the role of the <rpc> element in a NETCONF message exchange?

Accepted Answer

It acts as a wrapper enclosing the specific NETCONF method request sent by the client to the server.. The <rpc> element is the protocol envelope used by the client to send a request to the NETCONF server.

Answer

It defines the security credentials for SSH authentication.

Answer

It stores error logs returned by the Junos routing engine.

Answer

It terminates the NETCONF session upon completion.

Question 20

What is the standard IETF RFC that defines the core NETCONF protocol architecture and operations?

Accepted Answer

RFC 6241. RFC 6241 is the definitive IETF standard defining the NETCONF Configuration Protocol.

Answer

RFC 8040

Answer

RFC 4253

Answer

RFC 7950