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Automation Questions 3

January 24th, 2021 in ENCOR 350-401 Go to comments

Question 1

Explanation

YANG (Yet Another Next Generation) is a data modeling language for the definition of data sent over network management protocols such as the NETCONF and RESTCONF.

Question 2

Explanation

One of the best practices to secure REST APIs is using password hash. Passwords must always be hashed to protect the system (or minimize the damage) even if it is compromised in some hacking attempts. There are many such hashing algorithms which can prove really effective for password security e.g. PBKDF2, bcrypt and scrypt algorithms.

Other ways to secure REST APIs are: Always use HTTPS, Never expose information on URLs (Usernames, passwords, session tokens, and API keys should not appear in the URL), Adding Timestamp in Request, Using OAuth, Input Parameter Validation.

Reference: https://restfulapi.net/security-essentials/

We should not use MD5 or any SHA (SHA-1, SHA-256, SHA-512…) algorithm to hash password as they are not totally secure.

Note: A brute-force attack is an attempt to discover a password by systematically trying every possible combination of letters, numbers, and symbols until you discover the one correct combination that works.

Question 3

Explanation

The example below shows the usage of lock command:

def demo(host, user, names):
    with manager.connect(host=host, port=22, username=user) as m:
        with m.locked(target=’running’):
            for n in names:
                m.edit_config(target=’running’, config=template % n)

the command “m.locked(target=’running’)” causes a lock to be acquired on the running datastore.

Question 4

Explanation

The most common implementations of OAuth (OAuth 2.0) use one or both of these tokens:
+ access token: sent like an API key, it allows the application to access a user’s data; optionally, access tokens can expire.
+ refresh token: optionally part of an OAuth flow, refresh tokens retrieve a new access token if they have expired. OAuth2 combines Authentication and Authorization to allow more sophisticated scope and validity control.

Question 5

Explanation

Ansible works by connecting to your nodes and pushing out small programs, called “Ansible modules” to them. These programs are written to be resource models of the desired state of the system. Ansible then executes these modules (over SSH by default), and removes them when finished.

Chef is a much older, mature solution to configure management. Unlike Ansible, it does require an installation of an agent on each server, named chef-client. Also, unlike Ansible, it has a Chef server that each client pulls configuration from.

Question 6

Explanation

Accept and Content-type are both headers sent from a client (a browser) to a service.
Accept header is a way for a client to specify the media type of the response content it is expecting and Content-type is a way to specify the media type of request being sent from the client to the server.

The response was sent in XML so we can say the Accept header sent was application/xml.

Question 7

Explanation

Customer needs are fast evolving. Typically, a network center is a heterogenous mix of various devices at multiple layers of the network. Bulk and automatic configurations need to be accomplished. CLI scraping is not flexible and optimal. Re-writing scripts many times, even for small configuration changes is cumbersome. Bulk configuration changes through CLIs are error-prone and may cause system issues. The solution lies in using data models-a programmatic and standards-based way of writing configurations to any network device, replacing the process of manual configuration. Data models are written in a standard, industry-defined language. Although configurations using CLIs are easier (more human-friendly), automating the configuration using data models results in scalability.

Reference: https://www.cisco.com/c/en/us/td/docs/optical/ncs1000/60x/b_Datamodels_cg_ncs1000/b_Datamodels_cg_ncs1000_chapter_00.pdf

Question 8

Explanation

Missing Data Model RPC Error Reply Message
If a request is made for a data model that doesn’t exist on the Catalyst 3850 or a request is made for a leaf that is not implemented in a data model, the Server (Catalyst 3850) responds with an empty data response. This is expected behavior.

Reference: https://www.cisco.com/c/en/us/support/docs/storage-networking/management/200933-YANG-NETCONF-Configuration-Validation.html

Question 9

Explanation

ncclient is a Python library that facilitates client-side scripting and application development around the NETCONF protocol.

The above Python snippet uses the ncclient to connect and establish a NETCONF session to a Nexus device (which is also a NETCONF server).

Question 10

Question 11

Explanation

JSON syntax structure:
+ uses curly braces {} to hold objects and square brackets [] to hold arrays
+ JSON data is written as key/value pairs
+ A key/value pair consists of a key (must be a string in double quotation marks ""), followed by a colon :, followed by a value. For example: “name”:”John”
+ Each key must be unique
+ Values must be of type string, number, object, array, boolean or null
+ Multiple key/value within an object are separated by commas ,

JSON can use arrays. Arrays are used to store multiple values in a single variable. For example:

{
“name”:”John”,
“age”:30,
“cars”:[ “Ford”, “BMW”, “Fiat”]
}

In the above example, “cars” is an array which contains three values “Ford”, “BMW” and “Fiat”.

Note: Although our correct answer above does not have curly braces to hold objects but it is still the best choice here.

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