CompTIA Network+ N10-009 Study Notes

The Open Systems Interconnection (OSI) model, developed by the ISO in 1984, is a conceptual framework with seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.
Layer 1 (Physical): Manages raw data bits, electrical signals, and media like cables, hubs, and repeaters.
Layer 2 (Data Link): Handles node-to-node transfer and error detection; divided into MAC and LLC layers; associated with bridges, L2 switches, and NICs.
Layer 3 (Network): Manages logical addressing and routing using IP; devices include routers and L3 switches.
Layer 4 (Transport): Provides end-to-end data transfer using TCP (reliable) or UDP (fast); handles segmentation and reassembly.
Layer 5 (Session): Establishes, maintains, and terminates communication sessions between applications.
Layer 6 (Presentation): Translates, encrypts, and compresses data to ensure readability between network and application formats.
Layer 7 (Application): Interacts with users through protocols like HTTP, FTP, and SMTP.

Routers: Direct packets between different networks using routing tables and support NAT and QoS.
Switches: Connect devices locally; Layer 2 switches use MAC addresses, while Layer 3 switches incorporate IP routing.
Security Appliances: Firewalls filter traffic; IDS detects threats; IPS proactively blocks attacks.
Load Balancers: Distribute traffic across servers using algorithms like round-robin to ensure high availability.
Proxy Servers: Act as intermediaries; Forward proxies serve clients, and Reverse proxies manage server-side requests.
Storage Systems: NAS provides file-level access over a network; SAN provides high-performance block-level storage via Fibre Channel or iSCSI.
Wireless Infrastructure: Wireless Access Points (WAP) extend connectivity; Wireless Controllers manage configurations and security for multiple WAPs.

Deployment Models: Public (shared provider), Private (exclusive use), Hybrid (combined), and Hosted Private.
Service Models: IaaS (virtualized infrastructure), PaaS (development platform), and SaaS (ready-to-use software).
Scalability and Elasticity: Vertical scaling adds power to existing servers; Horizontal scaling adds more servers; Elasticity adjusts resources dynamically in real-time.
Multitenancy: Multiple customers share the same physical infrastructure with isolated environments.
Connectivity: VPNs are cost-effective over public internet; Direct Connect offers dedicated, low-latency, high-bandwidth links.
Gateways: Internet Gateways allow VPC traffic to reach the internet; NAT Gateways allow private instances secure outbound-only access.

Wireless Standards (IEEE 802.11):
- $802.11a$ : $54\,Mbps$ at $5\,GHz$ .
- $802.11b$ : $11\,Mbps$ at $2.4\,GHz$ .
- $802.11g$ : $54\,Mbps$ at $2.4\,GHz$ .
- $802.11n$ (Wi-Fi 4): $600\,Mbps$ at $2.4/5\,GHz$ .
- $802.11ac$ (Wi-Fi 5): $1300\,Mbps$ at $5\,GHz$ .
- $802.11ax$ (Wi-Fi 6/6E): Up to $9600\,Mbps$ at $2.4, 5,$ and $6\,GHz$ .
Wired Media:
- Twisted Pair: Cat 5e/6 ( $1\,Gbps$ ), Cat 6a/7 ( $10\,Gbps$ ), Cat 8 ( $25-40\,Gbps$ ).
- Fiber Optic: Single-mode (SMF) for long distances; Multimode (MMF) for shorter, high-speed campus links.
- Coaxial and Direct Attach Copper (DAC): Used for specific internet services or short-distance data center connections.

Physical Topologies: Star (central hub), Mesh (high redundancy), Bus, and Ring.
Data Center Designs: Spine and Leaf topology provides low-latency east-west traffic; Three-Tier models include Core, Distribution, and Access layers.
SD-WAN and SDN: Software-defined networking decouples the control and data planes for centralized management.
SASE: Integrates SD-WAN and security functions (Zero Trust, CASB) into a cloud-hosted service.

IPv4 Basics: $32$ -bit addresses; Private ranges defined by RFC1918; APIPA uses $169.254.x.x$ ; Loopback is $127.0.0.1$ .
IPv6 Features: $128$ -bit addresses; utilizes SLAAC for auto-configuration and suppresses address exhaustion.
DHCP (DORA Process): Discover, Offer, Request, Acknowledge; uses scopes, leases, and relay agents for cross-subnet management.
DNS: Maps hostnames to IPs; records include A (IPv4), AAAA (IPv6), CNAME (alias), MX (mail), and PTR (reverse).
Routing Protocols: Static (manual) vs. Dynamic (OSPF, EIGRP, BGP); uses NAT and PAT to conserve public IP addresses.

Monitoring Tools: SNMP (v1/v2c insecure, v3 encrypted); Syslog for log aggregation; SIEM for security event analysis.
Disaster Recovery (DR): Metrics include RPO (data loss threshold) and RTO (time to restore); Site types include Cold, Warm, and Hot sites.
Security Principles: CIA Triad (Confidentiality, Integrity, Availability); Least Privilege; Multi-Factor Authentication (MFA); Role-Based Access Control (RBAC).
Encryption: AES is common for data at rest; TLS and IPsec protect data in transit.
Physical Security: Includes MDF/IDF structured cabling, hot/cold aisle airflow management, and fire suppression systems (clean agents, water mist).