cisco.com
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Cisco.com is the official Cisco site offering product information, technical documentation, white papers, support, and learning resources related to networking technologies and protocols.
More resources on Network Protocols
Wireshark User's Guide
Official free resource for protocol dissection
Cloudflare Learning: Network Layer
Free articles on network protocols like IP
Beej's Guide to Network Programming
Free guide to socket programming and protocols
How the Internet Works in 5 Minutes
Simple explanation of network protocols
Introduction to TCP/IP
You use the Internet through your PC (Personal Computer), laptop, tablet, smartpad, and smartphone every day in everything you do. Through your own PC/laptop, you can easily learn everything about the Internet, and that is what this course is focused on. In this course ‘Introduction to TCP/IP,’ you will learn the operational functions of Internet technologies (which include IPv4, IPv6, TCP, UDP, addressing, routing, domain names, etc.) and your PC/laptop's security and gateway Internet setup and basic principles. In addition, through a simple Wireshark experiment, you will see the TCP/IP packets and security systems in action that are serving your PC/laptop, that serves you.
geeksforgeeks.org
GeeksforGeeks is a computer science education site offering tutorials, articles, and practice problems across programming, algorithms, data structures, and networking. It covers networking fundamentals and network protocols with step-by-step explanations of topics like the OSI model and TCP/IP, plus hands-on examples and quizzes to reinforce learning.