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Hands-On Network Programming with C

You're reading from   Hands-On Network Programming with C Learn socket programming in C and write secure and optimized network code

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Product type Paperback
Published in May 2019
Publisher Packt
ISBN-13 9781789349863
Length 478 pages
Edition 1st Edition
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Author (1):
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Lewis Van Winkle Lewis Van Winkle
Author Profile Icon Lewis Van Winkle
Lewis Van Winkle
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Table of Contents (26) Chapters Close

Title Page
Copyright and Credits
Dedication
About Packt Contributors Preface 1. Introducing Networks and Protocols FREE CHAPTER 2. Getting to Grips with Socket APIs 3. An In-Depth Overview of TCP Connections 4. Establishing UDP Connections 5. Hostname Resolution and DNS 6. Building a Simple Web Client 7. Building a Simple Web Server 8. Making Your Program Send Email 9. Loading Secure Web Pages with HTTPS and OpenSSL 10. Implementing a Secure Web Server 11. Establishing SSH Connections with libssh 12. Network Monitoring and Security 13. Socket Programming Tips and Pitfalls 14. Web Programming for the Internet of Things 1. Answers to Questions 2. Setting Up Your C Compiler on Windows 3. Setting Up Your C Compiler on Linux 4. Setting Up Your C Compiler on macOS 5. Example Programs 6. Other Book You May Enjoy

The DNS protocol

When a client wants to resolve a hostname into an IP address, it sends a DNS query to a DNS server. This is typically done over UDP using port 53. The DNS server then performs the lookup, if possible, and returns an answer. The following diagram illustrates this transaction:

If the query (or, more commonly, the answer) is too large to fit into one UDP packet, then the query can be performed over TCP instead of UDP. In this case, the size of the query is sent over TCP as a 16-bit value, and then the query itself is sent. This is called TCP fallback or DNS transport over TCP. However, UDP works for most cases, and UDP is how DNS is used the vast majority of the time.

It's also important to note that the client must know the IP address of at least one DNS server. If the client doesn't know of any DNS servers, then it has a sort of chicken-and-egg problem...

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