Computer Networks
OSI, TCP/IP, HTTP, DNS, TLS, sockets, routing, and the protocol internals every backend developer gets asked.
Networking Fundamentals
OSI Model (7 Layers)
The 7-layer reference model that explains how data moves across a network.
TCP/IP Model
The 4-layer model that the real internet actually runs on.
How Data Travels (Encapsulation & Frames)
How a message gets wrapped layer by layer and turned into bits on the wire.
IP Addressing (IPv4 & IPv6)
How IP addresses uniquely identify machines on the internet.
Subnetting & CIDR
Carving an IP block into smaller networks using prefixes and masks.
MAC Addresses & ARP
How devices on a LAN find each other using hardware addresses and ARP.
Ports & Sockets
How ports identify processes and sockets identify connections.
Transport Layer
TCP vs UDP
The two transport protocols that the internet runs on, and when to pick which.
TCP 3-Way Handshake
How TCP establishes a reliable connection in three messages.
TCP Connection Termination (4-Way)
How TCP gracefully closes a connection and why TIME_WAIT exists.
Reliable Delivery & Sequence Numbers
How TCP guarantees every byte arrives, in order, exactly once.
Flow Control & Sliding Window
How TCP prevents a fast sender from overwhelming a slow receiver.
Congestion Control (Slow Start, AIMD)
How TCP shares the network fairly without melting routers.
Network Layer & Routing
IP Routing & Routers
How routers decide where to forward each packet using routing tables.
Routing Algorithms (Distance Vector, Link State)
How routers learn paths to every network on the internet.
NAT (Network Address Translation)
How one public IP can hide an entire private network behind it.
ICMP, ping & traceroute
How ping and traceroute use ICMP and TTL to map the network.
VPN Basics
How VPNs tunnel traffic securely between machines or networks.
Application Layer Protocols
HTTP Basics (Methods, Status Codes, Headers)
The vocabulary of the web — verbs, response codes, and headers we send with every request.
HTTP/1.0 vs 1.1 vs 2 vs 3 (QUIC)
How HTTP evolved from one-connection-per-request to multiplexed streams over UDP.
DNS Deep Dive (Recursive vs Iterative, Records)
How a domain name turns into an IP address — the resolvers, record types, and caching behind every URL.
DHCP
How devices automatically get an IP address on a network — the DORA handshake.
SMTP, IMAP & POP3
The three email protocols — one to send, two to receive.
FTP & SFTP
File transfer protocols — old, plaintext FTP versus modern, secure SFTP over SSH.
SSH
Secure Shell — encrypted remote access, key-based auth, and port forwarding.
Web & Real-Time Communication
REST API Networking
Statelessness, idempotency, and caching headers — the network-level concerns of REST APIs.
WebSockets
Full-duplex communication between client and server over a single long-lived TCP connection.
Server-Sent Events (SSE)
One-way server-to-client streaming over plain HTTP — simpler than WebSockets when we only need push.
Long Polling vs Short Polling
Two HTTP-only ways to fake real-time updates — and the trade-offs between them.
gRPC & HTTP/2 Streams
Protobuf-based RPC over HTTP/2 streams — four call types and why it beats REST for service-to-service traffic.
CORS Deep Dive
Why browsers block cross-origin requests, how preflight works, and the headers that fix it.
Network Security
SSL/TLS Handshake
How the client and server agree on a shared secret before encrypted traffic flows.
Symmetric vs Asymmetric Encryption
Two flavors of encryption — and why TLS uses both.
Certificates & PKI
How browsers know they're really talking to bank.com — X.509 certs, CAs, and the chain of trust.
Common Attacks (DDoS, MITM, Spoofing, Replay)
The classic network attacks every backend engineer should know — and how we defend against them.
Firewalls (Stateful vs Stateless)
How firewalls decide what gets in and what gets dropped — packet filters, stateful inspection, and WAFs.
HTTP Security Headers (HSTS, CSP, etc.)
The headers we add to HTTP responses to harden web apps against common attacks.
Performance, Scaling & Debugging
Latency vs Bandwidth vs Throughput
Three terms that get conflated all the time — and the highway analogy that finally separates them.
CDN & Edge Networks
How content gets close to users — PoPs, anycast, cache hit/miss, and origin shielding.
Load Balancing (L4 vs L7)
Two ways to spread traffic across servers — fast and dumb (L4) vs smart and HTTP-aware (L7).
Forward Proxy vs Reverse Proxy
Two proxies, opposite jobs — one hides the client, the other hides the server.
Network Debugging Toolkit
The CLI tools we reach for when something on the network is broken.