🌐 Internet মূল কাঠামো
Internet = অসংখ্য Computer-এর Network of Networks। প্রতিটি Device-এর unique IP (IPv4: 32-bit, IPv6: 128-bit)।
🔍 DNS — Phone Book of Internet
মানুষ মনে রাখে google.com, Computer বোঝে 142.250.190.46। DNS এই Translation করে।
📡 Request-এর Journey
- Browser → DNS Resolver → Root → TLD → Authoritative
- TCP 3-way handshake (SYN → SYN-ACK → ACK)
- TLS handshake (HTTPS)
- HTTP Request → Server → Database → Response
- Browser render
📋 DNS Record Types
A → Domain → IPv4 AAAA → Domain → IPv6 CNAME → Domain → অন্য Domain MX → Mail Server TXT → SPF, DKIM, verification NS → Nameserver PTR → Reverse DNS
💻 হাতে-কলমে
dig google.com +trace nslookup -type=MX gmail.com curl -v https://google.com curl -I https://google.com ping -c 4 google.com traceroute google.com
🎓 মূল কথা ⭐
Internet = IP + DNS + TCP + HTTP। DNS issue = "Site Down" feel — actual Server চলছে।