20 TCP/UDP Interview Questions and Answers

Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are two of the most common protocols used in networking. When applying for a position in networking or network administration, it is likely that employers will expect you to have a strong understanding of both TCP and UDP. Understanding what questions you are most likely to encounter and how to properly answer them improves your chances of making a positive impression on the hiring manager. In this article, we discuss the most commonly asked TCP/UDP questions and how you should respond.

TCP/UDP Interview Questions and Answers

Here are 20 commonly asked TCP/UDP interview questions and answers to prepare you for your interview:

1. What are the differences between TCP and UDP?

TCP is a connection-oriented protocol, which means that it requires a connection to be established between two devices before any data can be sent. UDP is a connectionless protocol, which means that data can be sent without first establishing a connection. TCP is also a reliable protocol, which means that data is guaranteed to be delivered in the order in which it was sent. UDP is an unreliable protocol, which means that data may not be delivered in the order in which it was sent.

2. What is a socket in the context of network programming?

A socket is a communication endpoint that is used for interprocess communication. Sockets can be used to communicate over a network, and they can also be used for communication between processes on the same machine.

3. Is there any difference between sockets and ports? If yes, then what is it?

Sockets are the endpoints of a connection between two devices, while ports are the logical channels through which data is transmitted. In other words, a socket is the physical connection between two devices, while a port is the software-level channel that data passes through on its way between those two devices.

4. Can you explain how TCP connections work?

TCP connections work by first establishing a connection between two devices, typically a client and a server. Once the connection is established, data can be exchanged between the two devices. In order for data to be exchanged, the devices must agree on a set of rules, or a protocol, that will govern how the data is exchanged. Once the data exchange is complete, the connection is terminated.

5. How many ways can we create a socket in Python?

There are three ways to create a socket in Python. The first is to use the socket.socket() function. The second is to use the socket.create_connection() function. The third is to use the socket.fromfd() function.

6. What happens when packet loss occurs while using TCP/UDP?

When packet loss occurs while using TCP/UDP, the connection between the two devices will be interrupted. In order to re-establish the connection, the two devices will need to go through a process of retransmitting the lost packets.

7. What do you understand by data fragmentation?

Data fragmentation is the process of breaking up a data stream into smaller pieces so that it can be transmitted more efficiently. When the data stream is reassembled at the destination, it is typically done so in the same order that the fragments were originally sent.

8. What’s the maximum size allowed for a datagram?

The maximum size for a datagram is 65,535 bytes.

9. What’s the purpose of SACKs in TCP?

SACKs are used to provide reliability in TCP by allowing the receiver to tell the sender which parts of the data it has received and which parts it has not. This way, the sender can retransmit any data that the receiver may have missed.

10. What is the primary function of a router?

The primary function of a router is to connect two or more networks together. This allows for the exchange of information between the networks.

11. Can you explain the concept of windowing to me?

In computer networking, windowing is a technique used to improve the efficiency of data transmission. When data is sent over a network, it is divided into small packets. Each packet contains a certain amount of data, and each packet has a sequence number. The receiver of the data keeps track of the sequence numbers of the packets it receives, and sends an acknowledgement (ACK) back to the sender for each packet it receives. The sender keeps track of the ACKs it receives, and uses them to determine which packets have been received by the receiver.

The size of the window is the number of packets that can be sent before the sender must wait for an ACK. The larger the window, the more efficient the data transmission.

12. What do you know about the Nagle algorithm?

The Nagle algorithm is a congestion control algorithm that helps to improve network performance by reducing the number of small packets that are sent over the network. This algorithm is often used in conjunction with the TCP protocol.

13. Why does TCP use both ACK and SYN flags?

The ACK flag is used to acknowledge receipt of data, while the SYN flag is used to synchronize sequence numbers. Together, these flags help to ensure that data is properly received and that communication between devices is properly coordinated.

14. What do you understand about an HTTP request?

An HTTP request is a message sent from a client to a server asking for specific information. The request will include the method (e.g. GET, POST, etc.), the URL of the resource being requested, and various headers and parameters as needed. The server will then respond with the requested information, or an error message if the request could not be completed.

15. What’s the main advantage of using UDP over TCP?

UDP is a simpler protocol than TCP and does not require the overhead of establishing and maintaining a connection. This makes it more efficient and faster, although it does not provide the same reliability and ordering guarantees as TCP.

16. What are some practical uses of UDP?

UDP is often used for streaming media or VoIP applications where dropped packets are less noticeable than in other types of data transfer. It is also used in DNS lookups and in some online games.

17. What are the three way handshakes used for in TCP?

The three way handshakes are used for connection establishment and connection termination. In the first instance, the three way handshakes are used to establish a connection between two devices. This is done by the first device sending a SYN packet to the second device, which the second device then responds to with a SYN-ACK packet. The first device then responds with an ACK packet, completing the handshake. In the second instance, the three way handshakes are used to terminate a connection between two devices. This is done by the first device sending a FIN packet to the second device, which the second device then responds to with an ACK packet. The first device then responds with a FIN packet, completing the handshake.

18. What do you understand about the slow start protocol?

The slow start protocol is a congestion control mechanism used by TCP. The basic idea is that when a connection is first established, the sender will start by sending a small number of packets. If these packets are successfully received, then the sender will gradually increase the number of packets sent. This is done in order to avoid overwhelming the network and causing congestion.

19. What do you understand about exponential backoff? When should this be used?

Exponential backoff is a strategy used to help reduce congestion in a network. It works by increasing the amount of time between retransmissions of lost packets. This strategy should be used when there is a lot of traffic on a network and collisions are likely to occur.

20. What is head-of-line blocking? What causes it?

Head-of-line blocking is a problem that can occur in network communication, whereby a single blocked packet can stall the entire communication channel. This can happen because TCP/UDP communication is typically done in a serial fashion, so if one packet is blocked or lost, the rest of the packets cannot be processed until the first one is resolved. This can cause major delays in communication, and is a major problem that needs to be addressed in network design.