🌐 Networking Knowledge Base

TCP/IP 5-Layer Protocol Stack ExplorerClick any layer to inspect

L5

Application LayerPDU: Data / Message

HTTP/1.1HTTP/2HTTP/3HTTPSDNSgRPCWebSocketSSHSMTPFTP

L4

Transport LayerPDU: Segment / Datagram

TCPUDPQUICTLS (on TCP)DTLS

L3

Network LayerPDU: Packet

IPv4IPv6ICMPBGPOSPFIGMP

L2

Data Link LayerPDU: Frame

Ethernet (802.3)Wi-Fi (802.11)ARPVLANs (802.1Q)PPP

L1

Physical LayerPDU: Bits / Signal

Ethernet copper (Cat5e/6)Fiber (SMF/MMF)Wi-Fi (2.4/5GHz)USBRS-232

↓ Encapsulation (send)  |  ↑ Decapsulation (receive)

Click any layer to inspect its protocols and PDUs

Network Packet Encapsulation — Layer-by-Layer

L5 App

Application Payload

GET /api/v1/user HTTP/1.1
Host: api.example.com
Authorization: Bearer eyJhb...

Stage 1: Application Data

The application produces raw data — an HTTP request body, JSON payload, or binary message. No headers from lower layers yet. This is the PDU at the Application layer: a "Message" or "Data".

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A structured guide covering everything you need to know about computer networking — from low-level protocols to distributed API design — with Java/Spring examples and interview questions throughout.

Topics Covered

#	Topic	Description
1	OSI & TCP/IP Models	Layered models, encapsulation, ARP, ICMP, request journey, middlebox placement
2	MAC Addressing & Layer 2 Forwarding	EUI-48 MAC anatomy, CAM switch tables, ARP state machine, GARP failover, VXLAN
3	IP Addressing & Routing	IPv4/IPv6, CIDR subnetting math, BGP, OSPF, DHCP DORA, NAT translation tables
4	TCP, UDP & Transport Layer	Handshake, flow/congestion control, TCP state machine & leak diagnosis, PMTUD, Nagle
5	QUIC & Modern Transport	0-RTT resumption, stream multiplexing without HOL blocking, 3x anti-amplification, Stateless Reset, UDP GSO
6	HTTP & HTTPS	HTTP/1.1–3 evolution, TLS handshake, headers, caching, CORS
7	DNS Resolution	Root to authoritative resolution, record types, negative caching, K8s ndots:5 trap, Happy Eyeballs
8	CDN & Load Balancing	CDN architecture, LB algorithms, health checks, Anycast
9	Proxies, Firewalls, NAT & VPNs	Forward/reverse/SOCKS5 proxies, Netfilter conntrack, WireGuard vs IPsec, MSS clamping
10	Tor, Onion Routing & Privacy Networks	3-hop circuit telescoping, onion peeling cryptography, V3 rendezvous services, traffic analysis
11	Network Security	PKI trust chains, OCSP Stapling, TLS 1.3 anti-replay, RPKI BGP validation, SYN cookies, IPsec NAT-T
12	API Authentication & Authorization	Constant-time API keys, OAuth 2.0 PKCE, DPoP (RFC 9449), SPIFFE/SPIRE zero-trust mTLS
13	Socket Programming & I/O Models	5 Linux I/O models, epoll ET vs LT, SO_REUSEPORT, zero-copy sendfile, Virtual Thread carrier pinning
14	REST & gRPC API Design	REST, gRPC/protobuf, GraphQL, versioning, OpenAPI
15	WebSockets & Real-Time	WS protocol, SSE, long polling, Spring WebSocket
16	Network Performance & Optimization	Speed of light latency hierarchy, NIC ring buffers, SoftIRQ drops, FQ-CoDel bufferbloat, BBR vs CUBIC, kTLS
17	Service Mesh & Microservices Networking	Istio, Envoy, circuit breaker, service discovery, K8s
18	Network Troubleshooting Tools	tcpdump, Wireshark, curl, openssl, dig, nmap, ss
19	Application Protocols Reference	SMTP, FTP, SSH, SNMP, NTP, MQTT, WebRTC
20	Interview Questions — Master List	Top questions across all topics, conntrack table exhaustion, eBPF/XDP, MTU black hole

Java / Spring Focus

Java NIO, Netty, Spring WebFlux, Spring WebSocket, gRPC-Java, WebClient, Spring Security OAuth2, and Resilience4j examples are included throughout.