Cisco Interview Questions and Answers for Technical Profiles

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1. Define firewall and explain methods through which firewalls can be implemented
A firewall is a network security system that monitors and takes actions (permit or deny traffic) on the basis of policies defined explicitly. It can be performed by a single device, a group of devices, or by software running on a single device like a server.

2. Explain various mechanisms for building a Distributed file system.
Distributed Systems are the systems that make a single system image to users of the networks. The failure of one system in the network will not be coming into the picture of all other uses.

Characteristics of distributed file system

• Remote data/file sharing: It allows a file to be transparently accessed by processes of any node of the system irrespective of the file’s location. Example: Any process  ‘A’ can create the file and share it with other processes ‘B’ or ‘C’ and the same file can be accessed/modified process running in other nodes.
• User mobility: Users in the distributed systems are allowed to work in any system at any time. So, users need not relocate secondary storage devices in distributed file systems.
• Availability: Distributed file systems keep multiple copies of the same file in multiple places. Hence, the availability of the distributed file system is high and it maintains a better fault tolerance for the system.
• Data Integrity: A file system is typically shared by several users. Data saved in a transferred file must have its integrity protected by the file system. The correct synchronization of concurrent access requests from multiple users vying for access to the same file requires a concurrency control method. Atomic transactions, which are high-level concurrency management systems for data integrity, are frequently made available to users by file systems. 
• Performance: Performance is evaluated using the typical amount of time it takes to persuade a client. It must function in a manner comparable to a centralized file system.
• Diskless workstations: Distributed file systems allow the use of diskless workstations to reduce noise and heat in the system.  Also, diskless workstations are more economical than disk-full workstations. 

3. What is a pointer and what are the various types of pointer in C? 
A pointer is defined as a derived data type that can store the address of other C variables or a memory location. We can access and manipulate the data stored in that memory location using pointers.

Syntax

The syntax of pointers is similar to the variable declaration in C, but we use the ( * ) dereferencing operator in the pointer declaration.

datatype * ptr;

where

• ptr is the name of the pointer.
• datatype is the type of data it is pointing to.

4.What are the various types of sorting technique?
A Sorting Algorithm is used to rearrange a given array or list of elements according to a comparison operator on the elements. The comparison operator is used to decide the new order of elements in the respective data structure.

5. What’s the difference between C and C++?

C	C++
C was developed by Dennis Ritchie between the year 1969 and 1973 at AT&T Bell Labs.	C++ was developed by Bjarne Stroustrup in 1979.
C does no support polymorphism, encapsulation, and inheritance which means that C does not support object oriented programming.	C++ supports polymorphism, encapsulation, and inheritance because it is an object oriented programming language.
C is (mostly) a subset of C++.	C++ is (mostly) a superset of C.
Number of keywords in C: * C90: 32 * C99: 37 * C11: 44 * C23: 59	Number of keywords in C++: * C++98: 63 * C++11: 73 * C++17: 73 * C++20: 81
For the development of code, C supports procedural programming.	C++ is known as hybrid language because C++ supports both procedural and object oriented programming paradigms

6. What is OSI model and explain its 7 layers?
OSI stands for Open Systems Interconnection. It was developed by ISO – ‘International Organization for Standardization’, in the year 1984. It is a 7-layer architecture with each layer having specific functionality to perform. All these 7 layers work collaboratively to transmit the data from one person to another across the globe.

7. What’s the difference between mutex and semaphore?

Mutex	Semaphore
A mutex is an object.	A semaphore is an integer.
Mutex works upon the locking mechanism.	Semaphore uses signaling mechanism
Operations on mutex: Lock Unlock	Operation on semaphore: Wait Signal
Mutex doesn’t have any subtypes.	Semaphore is of two types: Counting Semaphore Binary Semaphore

8. What are Deadlocks?
  A deadlock is a situation where a set of processes are blocked because each process is holding a resource and waiting for another resource acquired by some other process.

9. What is a network congestion?
Network Congestion occurs when the traffic flowing through a network exceeds its maximum capacity. In most cases, congestion is a temporary issue with the network caused due to a sudden upsurge of traffic, however, sometimes, a network is continually congested, indicating a deeper problem.

10. What are various types of TCP timers?
TCP uses several timers to ensure that excessive delays are not encountered during communications. Several of these timers are elegant, handling problems that are not immediately obvious at first analysis.

11. What is inheritance and What are the different types of inheritance ?
The capability of a class to derive properties and characteristics from another class is called Inheritance. Inheritance is one of the most important features of Object-Oriented Programming.

12.What is an API?
API is an abbreviation for Application Programming Interface which is a collection of communication protocols and subroutines used by various programs to communicate between them.

13. What are various Keywords in C?
Keywords are predefined or reserved words that have special meanings to the compiler. These are part of the syntax and cannot be used as identifiers in the program.

14. What’s the differences between TCP and UDP?

Basis	Transmission Control Protocol (TCP)	User Datagram Protocol (UDP)
Type of Service	TCP is a connection-oriented protocol. Connection  orientation means that the communicating devices should establish a connection before transmitting data and should close the connection after transmitting the data.	UDP is the Datagram-oriented protocol. This is because  there is no overhead for opening a connection, maintaining a connection, or terminating a connection. UDP is efficient for broadcast and multicast types of network transmission.
Reliability	TCP is reliable as it guarantees the delivery of data to the destination router.	The delivery of data to the destination cannot be guaranteed in UDP.
Error checking mechanism	TCP provides extensive error-checking mechanisms.  It is because it provides flow control and acknowledgment of data.	UDP has only the basic error-checking mechanism using checksums.
Acknowledgment	An acknowledgment segment is present.	No acknowledgment segment.
Sequence	Sequencing of data is a feature of Transmission Control  Protocol (TCP). this means that packets arrive in order at the receiver.	There is no sequencing of data in UDP. If the order is required, it has to be managed by the application layer.

15. How is a TCP connection made?
TCP is a connection-oriented protocol and every connection-oriented protocol needs to establish a connection in order to reserve resources at both the communicating ends. 

16. What is Encapsulation?
Encapsulation is a fundamental concept in object-oriented programming (OOP) that refers to the bundling of data and methods that operate on that data within a single unit, which is called a class in Java

17. What are Logic Gates and its types ?
A semiconductor material’s electrical conductivity is somewhere between that of a conductor, such as metallic copper, and that of an insulator, such as glass. As the temperature rises, its resistivity reduces, whereas metals have the opposite effect.

18. What is virtual memory in OS ?
Virtual Memory is a storage allocation scheme in which secondary memory can be addressed as though it were part of the main memory. The addresses a program may use to reference memory are distinguished from the addresses the memory system uses to identify physical storage sites and program-generated addresses are translated automatically to the corresponding machine addresses. 

19. What is Cut-through Switching?
Cut-through is a packet-switching method, where the switch forwards a packet as soon as the destination address is processed without waiting for the entire packet to be received. The next packet is sent as soon as the previous one has been verified as reaching the recipient without waiting for the complete transmission of the previous packet.

20. What’s the difference between linked list and arrays ?

• Array: Arrays store elements in contiguous memory locations, resulting in easily calculable addresses for the elements stored and this allows faster access to an element at a specific index.
•  Linked List: Linked lists are less rigid in their storage structure and elements are usually not stored in contiguous locations, hence they need to be stored with additional tags giving a reference to the next element. 

21. What’s the difference between heap and stack ?

Parameter	STACK	HEAP
Basic	Memory is allocated in a contiguous block.	Memory is allocated in any random order.
Allocation and De-allocation	Automatic by compiler instructions.	Manual by the programmer.
Cost	Less	More
Implementation	Easy	Hard
Access time	Faster	Slower
Main Issue	Shortage of memory	Memory fragmentation
Locality of reference	Excellent	Adequate
Safety	Thread safe, data stored can only be accessed by the owner	Not Thread safe, data stored visible to all threads
Flexibility	Fixed-size	Resizing is possible
Data type structure	Linear	Hierarchical

22. What is Recovery Testing in Software Testing ?
System testing is a type of software testing that evaluates the overall functionality and performance of a complete and fully integrated software solution. It tests if the system meets the specified requirements and if it is suitable for delivery to the end-users. This type of testing is performed after the integration testing and before the acceptance testing.

23. What are various types of TCP timers?
TCP uses several timers to ensure that excessive delays are not encountered during communications. Several of these timers are elegant, handling problems that are not immediately obvious at first analysis

24. What is the difference between Structured Programming and Object Oriented Programming?

Structured Programming	Object-Oriented Programming
It is a subset of procedural programming.	It relies on concept of objects that contain data and code.
Programs are divided into small programs or functions.	Programs are divided into objects or entities.
It is all about facilitating creation of programs with readable code and reusable components.	It is all about creating objects that usually contain both functions and data.
Its main aim is to improve and increase quality, clarity, and development time of computer program.	Its main aim is to improve and increase both quality and productivity of system analysis and design.

25. What’s the Difference between Normalization and Denormalization?

Normalization	Denormalization
In normalization, Non-redundancy and consistency data are stored in set schema.	In denormalization, data are combined to execute the query quickly.
In normalization, Data redundancy and inconsistency is reduced.	In denormalization, redundancy is added for quick execution of queries.
Data integrity is maintained in normalization.	Data integrity is not maintained in denormalization.
In normalization, redundancy is reduced or eliminated.	In denormalization redundancy is added instead of reduction or elimination of redundancy.
Number of tables in normalization is increased.	Denormalization, Number of tables in decreased.

26. What are ACID properties?
A transaction is a single logical unit of work that accesses and possibly modifies the contents of a database. Transactions access data using read-and-write operations. 
In order to maintain consistency in a database, before and after the transaction, certain properties are followed. These are called ACID properties. 

27. Check if pair with given Sum exists in Array (Two Sum)
Two Sum using Hashing

This problem can be solved efficiently by using the technique of hashing. Use a hash_map to check for the current array value x(let), if there exists a value target_sum-x which on adding to the former gives target_sum. This can be done in constant time.

28. Next Permutation

Brute Force Approach :

• Find all possible permutations of the given array.
• Print the Next permutation right after the er given input sequence.

29. What is a trigger in SQL?

A trigger is a stored procedure in a database that automatically invokes whenever a special event in the database occurs. For example, a trigger can be invoked when a row is inserted into a specified table or when specific table columns are updated in simple words a trigger is a collection of SQL statements with particular names that are stored in system memory.

30. What is the difference between a structure and a class in C++?

Class	Structure
Members of a class are private by default.	Members of a structure are public by default.
An instance of a class is called an ‘object’.	An instance of structure is called the ‘structure variable’.
Member classes/structures of a class are private by default but not all programming languages have this default behavior eg Java etc.	Member classes/structures of a structure are public by default.
It is declared using the class keyword.	It is declared using the struct keyword.
It is normally used for data abstraction and further inheritance.	It is normally used for the grouping of data

31. Intersection of Two Linked Lists

Use Hashing

Basically, we need to find a common node of two linked lists. So we hash all nodes of the first list and then check the second list. 

Create an empty hash set. 

• Traverse the first linked list and insert all nodes’ addresses in the hash set. 
• Traverse the second list. For every node check if it is present in the hash set. If we find a node in the hash set, return the node.

32. The Celebrity Problem

Using Elimination Technique (Efficient):

The idea is to follow below to steps based on the above approach:

• If A knows B, then A can’t be a celebrity. Discard A, and B may be celebrity.
• If A doesn’t know B, then B can’t be a celebrity. Discard B, and A may be celebrity.

We will not use any extra space as will use spaces M[i][i] for storing whether i th person is a celebrity or not as these are by default 0, so if we find i th person is not a celebrity then we will mark M[i][i] as 1

33. Detect Cycle in a Directed Graph

Detect Cycle in a Directed Graph using DFS:

The problem can be solved based on the following idea:

To find cycle in a directed graph we can use the Depth First Traversal (DFS) technique. It is based on the idea that there is a cycle in a graph only if there is a back edge [i.e., a node points to one of its ancestors] present in the graph.

To detect a back edge, we need to keep track of the nodes visited till now and the nodes that are in the current recursion stack [i.e., the current path that we are visiting]. If during recursion, we reach a node that is already in the recursion stack, there is a cycle present in the graph.

34. ZigZag Tree Traversal

We can use a queue just like we used in Level Order Traversal. But in this case, we can also maintain a flag variable which keeps track of alternate level to reverse the order of the corresponding level traversal.flag==true implies we have to insert from left to right and flag==false means we have to insert element from right to left our answer arraylist.

35. Minimum number of jumps to reach end (Jump Game)
Minimum number of jumps to reach the end using Recursion: 

Start from the first element and recursively call for all the elements reachable from the first element. The minimum number of jumps to reach end from first can be calculated using the minimum value from the recursive calls. 

minJumps(start, end) = 1 + Min(minJumps(k, end)) for all k reachable from start.

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