Cisco TAC Engineer Interview Questions, Process, and Tips

Round duration - 40 minutes
Round difficulty - Easy

Technical round with questions based on DSA.

Q1. 
Reverse a Number Problem Statement
Create a program to reverse a given integer N. The output should be the reversed integer.
Note:
If a number has trailing zeros, their reversed version should not inclu...read more
Ans. 
Reverse a given integer while excluding trailing zeros.
• Create a program to reverse the given integer by converting it to a string and then reversing it.

• Remove any trailing zeros from the reversed string before converting it back to an integer.

• Handle the constraints of the input integer being between 0 and 10^8.

• Example: For input 1230, the output should be 321.
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Q2. 
Reverse a Linked List Problem Statement
You are given a Singly Linked List of integers. Your task is to reverse the Linked List by changing the links between nodes.
Input:
The first line of input contai...read more
Ans. 
Reverse a given singly linked list by changing the links between nodes.
• Iterate through the linked list and reverse the links between nodes.

• Use three pointers to keep track of the current, previous, and next nodes.

• Update the links while traversing the list to reverse it.

• Return the head of the reversed linked list.
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Q3. What is the difference in C++ between 'new int[5]' and 'malloc(5 * sizeof(int))'?
Ans. 
new int[5] is C++ specific and initializes the array with default values, while malloc(5 * sizeof(int)) is a C function and does not initialize the array.
• new int[5] is C++ specific and calls constructors for each element in the array.

• malloc(5 * sizeof(int)) is a C function and does not call constructors, leaving the array uninitialized.

• new int[5] returns a pointer to the first element of the array, while malloc(5 * siz...read more
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Round duration - 60 minutes
Round difficulty - Easy

Technical interview round with questions based on DSA and OOPS.

Q1. How do you dynamically allocate a 2D array in C?
Ans. 
Use double pointer to dynamically allocate memory for array of strings in C.
• Declare a double pointer to hold the 2D array of strings.

• Allocate memory for the rows first using malloc.

• Then allocate memory for each string in the row using malloc.

• Assign values to the strings in the array.

• Example: char **array = malloc(rows * sizeof(char *));

• Example: array[i] = malloc(strlen(str) + 1); strcpy(array[i], str);
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Q2. What are virtual functions in C++?
Ans. 
Virtual functions in C++ are functions that can be overridden in derived classes, allowing for polymorphic behavior.
• Virtual functions are declared using the 'virtual' keyword in the base class.

• They are used to achieve runtime polymorphism in C++.

• Derived classes can override the virtual functions defined in the base class.

• Example: class Base { public: virtual void display() { cout << 'Base class dis...read more
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Q3. What are virtual base classes?
Ans. 
Virtual base classes are classes that are inherited virtually to avoid multiple instances of the same base class in a derived class hierarchy.
• Virtual base classes are used in multiple inheritance to prevent the Diamond Problem.

• They are declared with the 'virtual' keyword in the base class.

• When a class inherits a virtual base class, the most derived class is responsible for initializing the virtual base class.

• Example: c...read more
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Round duration - 60 minutes
Round difficulty - Easy

Technical interview round with questions based on OS/Networking etc.

Q1. What is the system call that creates a separate connection?
Ans. 
The system call that creates a separate connection is fork()
• fork() is a system call in Unix-like operating systems that creates a new process by duplicating the existing process

• The new process created by fork() is called the child process, while the original process is called the parent process

• fork() is commonly used in network programming to create separate connections for handling multiple clients
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Q2. What does the epoll_wait() system call do?
Ans. 
epoll_wait() system call waits for events on an epoll instance
• Used in Linux for I/O event notification

• Blocks until one or more file descriptors become ready

• Returns the number of file descriptors ready for I/O operations
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Q3. What are the different protocols used in the transport layer?
Ans. 
Different protocols used in the transport layer include TCP, UDP, SCTP, and DCCP.
• TCP (Transmission Control Protocol) - reliable, connection-oriented protocol used for most internet communication

• UDP (User Datagram Protocol) - connectionless protocol used for applications where speed is more important than reliability

• SCTP (Stream Control Transmission Protocol) - supports multiple streams of data, used for telecommunicati...read more
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Q4. What is the difference between TCP and UDP?
Ans. 
TCP is a connection-oriented protocol that ensures reliable data delivery, while UDP is a connectionless protocol that focuses on speed.
• TCP is reliable and ensures data delivery by establishing a connection before sending data.

• UDP is faster but less reliable as it does not establish a connection before sending data.

• TCP is used for applications that require high reliability and error correction, such as web browsing and...read more
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Round duration - 60 minutes
Round difficulty - Easy

Technical interview round with questions based on Networking etc.

Q1. What is the purpose of ICMP?
Ans. 
ICMP is a protocol used for error reporting, diagnostics, and network management in IP networks.
• ICMP is used to report errors in packet delivery

• It is used for network diagnostics and troubleshooting

• ICMP messages are encapsulated within IP packets

• Examples include ping (echo request/reply) and traceroute
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Q2. What are the types of connection release supported by TCP?
Ans. 
TCP supports four types of connection release: active close, passive close, simultaneous close, and abortive close.
• Active close: Client initiates the connection release process by sending a FIN packet.

• Passive close: Server initiates the connection release process by sending a FIN packet.

• Simultaneous close: Both client and server send FIN packets to each other simultaneously.

• Abortive close: Connection is terminated abru...read more
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Q3. What protocols are used by the MAC layer?
Ans. 
The MAC layer uses protocols like CSMA/CA, CSMA/CD, and TDMA to manage access to the network.
• CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) is used in wireless networks to avoid collisions.

• CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is used in wired networks to detect and handle collisions.

• TDMA (Time Division Multiple Access) is used in networks where devices are assigned specific
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Q4. What is the ARP protocol?
Ans. 
ARP (Address Resolution Protocol) is a protocol used to map an IP address to a MAC address in a local network.
• ARP is used to resolve IP addresses to MAC addresses in a local network.

• It operates at the data link layer of the OSI model.

• ARP requests are broadcasted to all devices on the network.

• Example: When a device wants to communicate with another device on the same network, it uses ARP to find the MAC address correspo
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