200-901 Practice Test 21 — 15 Questions

Question 1

A network engineer is troubleshooting connectivity issues and wants to verify the path that packets take from a source to a destination IP address. Which OSI layer is primarily responsible for packet forwarding and routing?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Layer 3 - Network. The Network layer (Layer 3) is responsible for packet forwarding and routing, using logical IP addresses to determine the best path from source to destination. Protocols like IP (IPv4/IPv6) and routing protocols (e.g., OSPF, BGP) operate at this layer to make forwarding decisions. The traceroute command is a common tool that leverages Layer 3 TTL (Time-to-Live) fields to map the path packets take.

Answer

Layer 4 - Transport

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Layer 1 - Physical

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Layer 2 - Data Link

Question 2

A developer is writing unit tests for a Python module that parses show command output from network devices. The tests must be deterministic and must not depend on real devices or the network. Which TWO practices should the developer apply? (Choose two.)

Accepted Answer

Use unittest.mock to replace the function that opens an SSH connection to the device with a stub that returns captured output.. Deterministic, device-independent parsing tests come from replacing live I/O with controlled substitutes and asserting against known data. Mocking the SSH layer removes network dependency, while fixture files supply stable input and expected results. Together these practices make the unit tests repeatable and safe to run in CI without any real routers or switches.

Answer

Run the test suite against a production router to confirm the parser handles real output.

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Run tests only in a lab environment where devices are always powered on and reachable.

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Add time.sleep calls between assertions to allow the device to respond before checking results.

Question 3

A developer is designing a Python application that must handle failures when making REST API calls to a Cisco DNA Center controller. The application should retry a failed request only if the HTTP status code indicates a server-side error (5xx) or a timeout occurs, but should not retry on client errors (4xx). The developer wants to implement this using a decorator. Which Python library provides a ready-to-use retry decorator that can be configured to retry on specific exceptions and HTTP status codes?

Accepted Answer

tenacity. Tenacity is a dedicated retrying library that offers a decorator with extensive configuration options, including retrying on specific exceptions and stop conditions. It can be easily integrated with HTTP status code checks. The other libraries either lack a retry decorator or require manual implementation, making tenacity the correct choice for this scenario.

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urllib3

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functools

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requests

Question 4

A developer is building a Python application that must handle configuration data in multiple formats (JSON, YAML, XML) and provide a consistent interface for reading and writing. The application may add new formats later. Which design pattern best supports this extensibility while keeping the client code decoupled from concrete implementations?

Accepted Answer

Factory method pattern with an abstract parser interface. The factory method pattern is ideal because it encapsulates object creation, letting the client work with an abstract parser interface while subclasses or factory methods handle instantiation of concrete parsers for JSON, YAML, or XML. This decouples client code from specific formats and allows new formats to be added without changing existing code, satisfying extensibility.

Answer

Singleton pattern with a global configuration manager

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Observer pattern to notify components when configuration changes

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Adapter pattern to convert each format to a common internal representation

Question 5

A developer is working on a Git repository and needs to temporarily save changes that are not ready to be committed so they can switch to another branch to fix a bug. Which Git command should the developer use to stash the current changes?

Accepted Answer

git stash. The git stash command is designed to temporarily store modifications to tracked files and the staging area, allowing a clean working directory. This enables switching branches or performing other operations without committing incomplete work. The stashed changes can be reapplied later with git stash pop or git stash apply, making it ideal for the described scenario.

Answer

git commit -m "WIP"

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git branch temp

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git checkout -- .

Question 6

What is the primary function of a switch in a network?

Accepted Answer

Forward frames based on MAC addresses. Switches operate at Layer 2 and forward frames based on MAC addresses within a LAN.

Answer

Amplify wireless signals

Answer

Forward packets based on IP addresses

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Convert data to electrical signals

Question 7

A developer is building a Python script that calls the Cisco Webex Rooms API. The API returns a JSON error response with HTTP status code 429. The script currently retries immediately in a tight loop, but the errors persist. What should the developer implement to correctly handle this response?

Accepted Answer

Read the Retry-After response header and wait that many seconds before retrying the request.. HTTP 429 signals that the client has exceeded the API rate limit. Cisco Webex APIs return a Retry-After header indicating how long to wait before the next request. Reading and honoring that value prevents further throttling and is the standard remediation. Immediate retries, changing methods, or refreshing tokens do not address the underlying rate-limit condition.

Answer

Change the HTTP method from GET to POST and resend the request.

Answer

Set the Authorization header to a new access token and resend the request immediately.

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Add a Content-Type: application/json header and resend the request.

Question 8

When making API calls to Cisco Meraki Dashboard, what header must be included for authentication?

Accepted Answer

X-Cisco-Meraki-API-Key: <key>. Cisco Meraki Dashboard API uses a custom header for authentication rather than standard HTTP authentication schemes. The header `X-Cisco-Meraki-API-Key` must be included with the API key as its value. This is explicitly documented in the Meraki API reference and is required for all API requests to authenticate the caller.

Answer

Authorization: Basic <base64>

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Authorization: Bearer <token>

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Api-Key: <key>

Question 9

A developer is building a Python script that calls the Cisco Webex Rooms API. The script must handle rate limiting gracefully by reading the response headers when the API returns HTTP 429. Which response header should the script inspect to determine how long to wait before retrying?

Accepted Answer

Retry-After. When the Webex API throttles a client with HTTP 429, it includes the Retry-After header to specify the number of seconds to wait. Reading this header allows the script to implement an appropriate backoff, respecting the service's limits and avoiding further penalties. The other headers serve different purposes and do not provide rate-limit timing information.

Answer

X-RateLimit-Reset

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Location

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WWW-Authenticate

Question 10

A network engineer is using the Cisco DNA Center API to retrieve a list of all sites. The API response is a JSON object with a 'response' array containing site objects. The engineer wants to extract the name of each site. Which Python code snippet correctly parses the JSON response and prints each site name?

Accepted Answer

for site in response.json()['response']:
    print(site['name']). The Cisco DNA Center API returns site data within a top-level 'response' array. To print each site name, the code must parse the JSON, access the 'response' list, iterate over each site dictionary, and print the 'name' value. The correct snippet does exactly that, while the others either misidentify the key or attempt to iterate over the wrong structure.

Answer

for site in response.json():
    print(site['name'])

Answer

print(response.json()['name'])

Answer

for site in response.json()['sites']:
    print(site['name'])

Question 11

A developer is testing a REST API endpoint using curl. The API requires an API key to be sent in the HTTP header 'X-API-Key'. Which curl command correctly includes the API key?

Accepted Answer

curl -H "X-API-Key: abc123" https://api.example.com/resource. The -H flag in curl is used to add custom headers to an HTTP request. Since the API requires the API key in the 'X-API-Key' header, using -H with the appropriate header string is the correct approach. This ensures the key is transmitted as an HTTP header, which the API will validate.

Answer

curl -G "X-API-Key=abc123" https://api.example.com/resource

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curl -u "X-API-Key:abc123" https://api.example.com/resource

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curl -d "X-API-Key=abc123" https://api.example.com/resource

Question 12

Match each YAML structure to its description.

Accepted Answer

Mapping: An unordered set of key-value pairs, each separated by a colon and space.. In YAML, a mapping (dictionary) uses key: value pairs; a sequence (list) uses '- ' items; a scalar is a single value. The distractors swap definitions or apply collection concepts to scalars.

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Mapping: An ordered list of items, each prefixed with a dash and space.

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Sequence: An unordered set of key-value pairs, each separated by a colon and space.

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Scalar: A collection of key-value pairs or items.

Question 13

A developer maintains a Python package that other teams import. The package's setup.py currently pins an HTTP library to an exact version, and a consuming team reports that pip refuses to install their project because they require a newer minor release of the same library. Which change to the dependency specification best resolves the conflict while still protecting against breaking major upgrades?

Accepted Answer

Replace the exact pin with a compatible-release specifier such as requests>=2.28,<3.0 so minor and patch updates are allowed.. Dependency specifications should express the range the package actually supports. A lower bound with an upper bound below the next major version allows compatible minor and patch upgrades, which satisfies the consuming team's requirement while still guarding against breaking changes. Exact pins and removed declarations either block valid upgrades or leave the dependency undeclared.

Answer

Raise the pin to the newest available exact version, such as requests==2.31.0, so both projects use the same release.

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Pin the library to a specific older major version such as requests==1.2.3 to guarantee compatibility with existing code.

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Remove the library from the dependency list entirely so pip installs whichever version the consuming project happens to request.

Question 14

A developer is designing a Python application that will consume multiple REST APIs from different Cisco platforms. The application must handle common API behaviors such as authentication, rate limiting, and error responses. Which TWO of the following are best practices for making the application robust and maintainable? (Choose two.)

Accepted Answer

Implement exponential backoff when retrying requests after receiving 5xx errors.. Implementing exponential backoff for retries and using a shared HTTP session are both best practices that enhance robustness and maintainability. Exponential backoff handles transient errors gracefully, while a session improves performance and simplifies authentication management. Together, they help build a resilient application that can handle common API behaviors effectively.

Answer

Ignore HTTP status codes and parse the response body for error messages.

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Hard-code API keys and tokens directly in the source code for simplicity.

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Always use synchronous requests to simplify code and avoid concurrency issues.

Question 15

Drag and drop the steps to troubleshoot a network connectivity issue using the OSI model from bottom to top.

Accepted Answer

Check physical cables and interfaces, then verify data link layer, then verify network layer, then verify transport layer, then verify application layer.. Troubleshooting follows the OSI model from physical up to application to systematically isolate the problem.

Answer

Check application layer, then transport layer, then network layer, then data link layer, then physical layer.

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Check physical cables and interfaces, then verify network layer, then verify transport layer, then verify application layer, skipping data link layer.

Answer

Check network layer first, then physical cables and interfaces, then data link layer, then transport layer, then application layer.