Dev Blog

Summary ​

Conclusions ​

Network applications exchange data through the TCP/IP protocol stack: IP delivers packets between computers by address, while TCP and UDP deliver data between programs by port. TCP establishes a connection and reliably transfers a byte stream in the correct order; UDP quickly transfers individual datagrams without delivery guarantees but supports broadcasting. In .NET a socket is represented by the Socket class, and the TcpListener, TcpClient, NetworkStream, and UdpClient classes simplify common tasks. Because TCP does not preserve message boundaries, the application protocol defines them with a line delimiter or a length prefix, and it also describes commands, response codes, session states, limits, and a version. A server serves multiple clients with asynchronous tasks, protects shared data with thread-safe collections and locks, and shuts down gracefully via a cancellation token. Reliable network code handles SocketException and IOException, limits operations in time, validates input, encrypts traffic with TLS, and is checked with Windows diagnostic tools.

Self-check questions ​

  1. What layers does the TCP/IP model have? What is each layer responsible for?
  2. How do IPv4 and IPv6 addresses differ? What do the addresses 127.0.0.1 and 0.0.0.0 mean?
  3. What are ports for? What port ranges exist?
  4. How do you get IP addresses for a domain name in C#?
  5. How do the TCP and UDP protocols differ? Give examples of where they are used.
  6. What is the TCP three-way handshake?
  7. What steps do a server and a client that use the Socket class perform?
  8. What does the ReceiveAsync method return? What does a result of 0 mean?
  9. What is the purpose of the TcpListener, TcpClient, and NetworkStream classes?
  10. Why do you set AutoFlush and UTF8Encoding(false) for a StreamWriter over a network stream?
  11. Why must message boundaries be defined in a TCP stream? What approaches exist?
  12. What is network byte order? How do you write a number in big-endian format?
  13. What does an application protocol describe? What are response codes and a protocol version for?
  14. How does a server serve multiple clients at the same time? How do you protect shared data?
  15. How do you stop a server and a client gracefully?
  16. How do you send a UDP broadcast message, and what is it used for?
  17. When does the Windows Firewall prompt appear, and what happens if you cancel it?
  18. How do you set a timeout for a network operation?
  19. How do you check which ports a computer is listening on and which connections are established?