🕸️ शाळेच्या पद्धतीने networking शिका

# the 60-second wow — real packets, no libraries:
git clone https://github.com/BaluRaut/learn-networking-school.git && cd learn-networking-school
python3 net/demo.py                # TCP handshake, lossy UDP, a DNS question by hand, HTTP by hand, a TLS certificate
bash net/lab.sh example.com        # the debugging ladder: dig → ping → traceroute → nc → openssl → curl

तुम्हाला काय दिसायला हवे (छाटलेले — यश असे दिसते):

── TCP — the registered post: connect (handshake), then bytes arrive complete and in order
   my socket ('127.0.0.1', NNNNN) ↔ the clerk's socket ('127.0.0.1', NNNNN)   (ip:port on both ends = one connection)
   sent 3 pieces; the clerk answered: receipt: 31 bytes from 127.0.0.1:NNNNN
   the shape: a connection first, then a reliable ordered byte stream — you add the message boundaries (newline, length, HTTP)

── UDP — the loudspeaker: no connection, one datagram at a time, and some never arrive
   10 announcements made, 6 reached the corridor, 6 heard: ['announcement 0', 'announcement 2', 'announcement 4', 'announcement 5', 'announcement 7', 'announcement 9']
   the shape: cheap and fast, no ordering, no retransmit — DNS, video, games; anything else wants TCP

── Ports — room numbers: a quick knock on the usual doors of this machine
   127.0.0.1:22    ssh                          closed
   127.0.0.1:80    http                         closed
   127.0.0.1:443   https                        closed
   127.0.0.1:NNNNN  postgres                     open  ← someone is listening
   127.0.0.1:NNNNN  redis                        closed
   127.0.0.1:NNNNN  the API school's counter     closed
   127.0.0.1:NNNNN  the auth demo                closed
   the shape: an address says WHICH computer, a port says WHICH program; 0–1023 are the well-known rooms

── DNS — the directory: ask 8.8.8.8 'what is the address of example.com?' — one UDP packet each way
   sent 29 bytes · got 61 bytes · id matches: True · answers: 2 · flags 0x8180
   A record → 172.66.147.243   ttl 300s  (the directory says: cache me this long)
   A record → 104.20.23.154   ttl 300s  (the directory says: cache me this long)
   the shape: a name → an IP, cached by TTL, asked over UDP port 53; 'is it DNS?' is the first question of every outage

── HTTP — the slip in the envelope: a GET to example.com, typed by hand on port 80
   → GET / HTTP/1.1 · Host: example.com
   ← HTTP/1.1 200 OK · Content-Type: text/html
   ← body: 571 bytes   (HTTP is just text over a TCP stream; the API school lives one layer up)

── TLS — the sealed envelope: handshake with example.com:443 and read its certificate
   protocol TLSv1.2 · cipher ECDHE-ECDSA-CHACHA20-POLY1305
   certificate for: example.com   issued by: SSL Corporation   valid until: Oct 27 22:17:21 2026 GMT
   also valid for: ['example.com', '*.example.com']
   the shape: the server proves its name with a certificate a CA signed; then the envelope is sealed — HTTPS, and every 'S'

── Route — which corridor? the address this machine would use to reach the internet, and its default gateway
   my outward-facing address: 192.168.x.x   (a private address → NAT at the gate turns it into the school's one public address)
   run `traceroute 8.8.8.8` (or `tracert`) to see every corridor: your router → your ISP → an exchange → Google; each hop is a router forwarding by prefix

✅ the post room: addresses and rooms (IP:port) · registered post vs loudspeaker (TCP/UDP) · the directory (DNS) · the slip (HTTP) · the seal (TLS) · the corridors (routes)

🗺️ संपूर्ण चित्र — एक आकृती, पूर्ण कोर्स

संपूर्ण कोर्स एका कॅनव्हासवर. 4K आवृत्तीसाठी क्लिक करा.

📮 भाग 1 — पोस्ट (धडे 1–6)

एक git ब्रँच = एक कल्पना; ब्रँच 04 मध्ये धडे 01–04 आहेत. लॅब साध्या Python 3 आणि तुमच्या मशीनवर आधीच असलेल्या साधनांनी चालतात.

🏗️ भाग 2 — इमारत (धडे 7–12)

तुमचा लॅपटॉप आणि production मधला server यांच्यामधले सगळे, प्रत्येक तुकडा तुमच्याकडे आधीच असलेल्या साधनांनी दाखवलेला.

📐 धड्यांच्या आकृत्या — क्रमांक अनुसरा

प्रत्येक धडा एका क्रमांकित बॉक्स-आणि-बाण आकृतीत — स्वतंत्र पानावरही.