Cisco CCNA : visual study guide

OSI Model — 7 Layers

The 7 layers of the OSI model: what each one does, and how data gets wrapped as it travels.

🖼️

Ethernet Frames

The structure of a Layer 2 Ethernet frame — preamble, MAC addresses, EtherType, payload, and FCS.

🤝

Medium

TCP 3-Way Handshake

How two computers establish a reliable connection before any data is sent.

📦

UDP: When to Use It and Why

Why UDP's simplicity makes it the right choice for DNS, video streaming, VoIP, and gaming — the tradeoffs between TCP reliability overhead and UDP's speed, plus how QUIC builds reliability on top of UDP.

📍

IP Addresses Explained

Public vs private IPs, what they mean, and how NAT lets millions of devices share one public IP.

Subnets & Routing

How networks are divided into subnets and how routers forward packets between them.

6️⃣

IPv6 Addresses

IPv6 address format, types (link-local, global, multicast), NDP replacing ARP, and dual-stack operation.

🔢

IPv6 Addressing: Prefixes, Scopes & Address Types

How IPv6 addressing works beyond the basics — address format and compression rules, link-local vs global unicast vs ULA, prefix delegation (PD) from ISP to CPE, address scopes and their routing implications, and why every interface gets multiple IPv6 addresses.

🔢

IPv6 SLAAC — Auto-Configuration

How IPv6 devices configure their own addresses without DHCP using router advertisements and EUI-64 or random IIDs.

🏢

Three-Tier Network Architecture

The access, distribution, and core layers of enterprise networks — how traffic flows from a laptop to the internet.

🌿

Spine-Leaf Data Center Topology

How modern data centers use a spine-leaf fabric to provide predictable latency, high bandwidth, and easy horizontal scaling.

📶

How WiFi Works

802.11 association, channels, WPA2 authentication, and why WiFi is slower than wired.

⚡

Power over Ethernet (PoE)

How PoE (IEEE 802.3af/at/bt) delivers DC power over Ethernet cables to IP cameras, access points, and VoIP phones — including power negotiation, budget management, and the difference between PoE standards.

Network access

🏷️

MAC Addresses & ARP

What MAC addresses are, how ARP discovers them, and what happens when two devices want to talk.

📢

Broadcast, Multicast & Unicast

The three ways to address network traffic: one-to-one, one-to-group, and one-to-all.

🔀

Switches & VLANs

How switches learn MAC addresses, and how VLANs segment a network into isolated broadcast domains.

🔀

Ethernet Switching: MAC Tables, Flooding & Port Security

How Layer 2 switches work in depth — MAC address table learning and aging, unknown unicast flooding, broadcast domain containment, MAC flooding attacks and port security, and why switches outperform legacy hubs.

🌳

Spanning Tree Protocol

How STP eliminates loops in Ethernet networks by blocking redundant ports, electing a root bridge, and converging after a topology change.

🌳

STP vs RSTP: Spanning Tree Loop Prevention

How Spanning Tree Protocol prevents broadcast storms by blocking redundant paths — root bridge election, port roles, the slow STP convergence problem, and how RSTP achieves sub-second convergence with proposal/agreement.

🔗

Link Aggregation (LACP/802.3ad)

How LACP bonds multiple physical links into a single logical channel, distributing traffic across them for both redundancy and increased bandwidth.

🔗

LACP & Link Bonding: Aggregated Link Internals

How LACP (802.3ad) negotiates link aggregation between switches, LAG hashing algorithms that determine which link each flow uses, active vs passive LACP modes, LACP PDU exchange and port priority, bonding modes in Linux, and why LAG doesn't double throughput for a single TCP flow.

🔐

WEP → WPA → WPA2 → WPA3

The evolution of WiFi security protocols: why WEP was broken, how WPA patched it, what WPA2 got right, and what WPA3 adds.

📶

WPA2 — WiFi Authentication

How WPA2 authenticates devices to a WiFi network and derives unique per-session encryption keys via the 4-way handshake.

📡

Wi-Fi Roaming — 802.11r

How devices seamlessly hand off between access points as you walk through a building, and why 802.11r Fast BSS Transition eliminates the auth delay.

IP connectivity

IP Routing: How Routers Forward Packets

How a router makes forwarding decisions — longest prefix match, routing table vs FIB, administrative distance between routing protocols, recursive next-hop resolution, and what happens at each hop across the internet.

Static Routing

How manually configured static routes direct packets, why default routes matter, and how floating static routes provide automatic failover.

🗂️

OSPF — Link State Routing

How OSPF routers discover neighbors, flood link state advertisements, and compute shortest paths with Dijkstra's algorithm.

OSPF Areas & LSA Types: Scaling Link-State Routing

How OSPF uses areas to limit flooding scope — area 0 backbone, stub/NSSA/totally stubby area types, ABR and ASBR roles, LSA types 1–7, and why area design prevents the O(n²) LSDB problem in large networks.

Routing Algorithms: Link State vs Distance Vector

How link-state (OSPF) and distance-vector (RIP) algorithms discover topology and compute paths — Dijkstra's SPF, the Bellman-Ford equation, count-to-infinity, and why IS-IS and OSPF dominate modern networks.

📏

RIP — Distance Vector Routing

How RIP routers share routing tables with neighbors, count hops to build a network map, and why RIP is limited to small networks.

⚖️

ECMP Load Balancing

How routers distribute traffic across multiple equal-cost paths using hashing, and the reordering problems that arise when paths change.

⚡

Network Convergence: How Routes Propagate After Failure

What happens in the seconds after a network link fails — IGP convergence with OSPF LSA flooding, BGP withdrawal propagation, the role of timers, and why convergence time determines how long users see an outage.

IP services

🔄

NAT — Network Address Translation

How your router lets multiple devices share one public IP address using port mapping.

🔺

NAT Types: Full Cone, Symmetric, and Hairpinning

The four types of NAT (Full Cone, Restricted Cone, Port Restricted, Symmetric) and how they affect peer-to-peer connectivity — plus NAT hairpinning for same-network communication.

🪪

DHCP — Getting an IP Address

The DORA process: how your device automatically gets an IP, subnet mask, gateway, and DNS server.

📋

DHCP Relay & Snooping

How DHCP relay agents forward broadcasts across subnets, and how DHCP snooping prevents rogue DHCP servers from hijacking address assignment.

📖

DNS Resolution

How a domain name like 'example.com' gets translated into an IP address before connecting.

⏱️

NTP Time Synchronization

How computers on the internet keep their clocks accurate using the Network Time Protocol hierarchy.

⏰

NTP Stratum Hierarchy

How the NTP stratum hierarchy distributes accurate time from atomic clocks to billions of devices, with clock selection, drift correction, and leap seconds.

📊

SNMP Monitoring

How network management systems poll routers and switches with SNMP to collect metrics, and how traps alert on failures.

🚨

SNMP Traps & Alerts

How network devices send unsolicited SNMP Trap messages to NMS when events occur — link down, CPU spike, temperature threshold — and v3 authentication.

🎚️

QoS — Traffic Prioritization

How routers use DSCP markings and queuing to guarantee voice quality while allowing bulk transfers — ensuring VoIP stays crystal clear even during downloads.

📶

QoS Deep Dive: DSCP Marking and Queuing

How DSCP markings classify traffic at the IP layer, how routers queue packets into priority lanes, and why VoIP needs strict priority queuing while video needs bandwidth guarantees.

💻

Medium

SSH — Secure Shell

How SSH establishes an encrypted tunnel using key exchange, host authentication, and public-key login.

📁

FTP File Transfer

How FTP uses two separate TCP connections — one for commands, one for data — to transfer files.

Security fundamentals

🔒

Network ACLs vs Security Groups

How AWS Network ACLs (stateless) and Security Groups (stateful) differ, when to use each, and how they interact to create layered cloud network security.

🛡️

Firewall Rules

How firewalls inspect traffic and block or allow connections based on rules.

🔍

DHCP Snooping & Dynamic ARP Inspection

How DHCP snooping prevents rogue DHCP servers from hijacking client IP assignments, and how Dynamic ARP Inspection (DAI) uses the snooping table to block ARP spoofing attacks.

☠️

ARP Spoofing Attack

How an attacker poisons ARP caches to intercept all traffic on a local network (Man-in-the-Middle).

🛡️

ARP Spoofing Defense

How Dynamic ARP Inspection (DAI) and static ARP entries protect against ARP poisoning attacks that enable man-in-the-middle on LAN.

🪪

802.1X / EAP — Port-Based Auth

How enterprise Wi-Fi and wired networks authenticate every device before granting network access using RADIUS and EAP.

🎫

RADIUS & TACACS+: Network Authentication

How RADIUS and TACACS+ centralize authentication for network devices and VPN users — AAA (Authentication, Authorization, Accounting), and why enterprises use RADIUS for WiFi/VPN and TACACS+ for device management.

🔒

VPN Tunnel

How a VPN encrypts your traffic and hides your real IP address from websites and ISPs.

🐲

WPA3 — SAE Handshake

How WPA3's Simultaneous Authentication of Equals (Dragonfly) eliminates offline dictionary attacks and provides forward secrecy.

Automation and programmability

🧠

SDN & OpenFlow

How Software-Defined Networking separates the control plane from the data plane, letting a centralized controller program forwarding rules across the entire network.

🤖

Network Automation: NETCONF, YANG & Ansible

How modern network automation replaces CLI scripting with structured data — NETCONF operations over SSH, YANG data models, and Ansible's network modules for idempotent configuration management.

🌐

SD-WAN: Software-Defined WAN

How SD-WAN intelligently routes enterprise traffic across multiple WAN links — MPLS, broadband, LTE — using centralized policy, real-time path quality monitoring, and application-aware routing.

🔌