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OSI and TCP/IP Models — What Every Developer & Sysadmin Should Know
Practical comparison of the 7-layer OSI model and 4-layer TCP/IP model, packet encapsulation, and bottom-up network debugging techniques.
TXT Records — SPF, DKIM, and DMARC Syntax Masterclass
Complete beginner guide to writing, parsing, and debugging SPF, DKIM, and DMARC TXT records, understanding qualifiers, tags, and avoiding the 10-lookup limit.
Debugging DNS with dig, host, and nslookup — Complete Sysadmin Toolkit
Master DNS troubleshooting with dig, host, and nslookup, trace root-to-leaf resolution, understand RCODE errors (NXDOMAIN, SERVFAIL), and diagnose cache delays.
curl — Command Line HTTP Client & API Debugger
Complete beginner guide to curl, testing REST APIs, inspecting HTTP response headers, verifying SSL/TLS certificates, and debugging response timing with command flag breakdowns.