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Network Fundamentals for CCNA 200-301

Network Fundamentals covers the core building blocks of data networks, including network types, topologies, the OSI and TCP/IP models, and basic device roles. This topic accounts for approximately 20% of the CCNA 200-301 exam.

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Network Types

  • LAN (Local Area Network): Covers a small geographic area such as an office or building. Typically uses Ethernet (IEEE 802.3) or Wi-Fi (IEEE 802.11).
  • WAN (Wide Area Network): Spans large geographic areas, connecting multiple LANs. Common WAN technologies include MPLS, leased lines, and broadband.
  • MAN (Metropolitan Area Network): Covers a city-sized area, larger than a LAN but smaller than a WAN.
  • WLAN (Wireless LAN): A LAN that uses wireless radio transmission rather than physical cables.

Network Topologies

  • Star: All devices connect to a central switch or hub. Most common in modern LANs.
  • Bus: All devices share a single communication line. Legacy topology, rarely used today.
  • Ring: Devices are connected in a circular loop. Used in older Token Ring networks.
  • Mesh: Devices interconnect directly with many or all other devices. Provides redundancy.

The OSI Model (7 Layers)

The OSI model provides a framework for understanding how data moves through a network. Each layer has distinct responsibilities:

  • Layer 7 – Application: User-facing protocols (HTTP, FTP, DNS, SMTP).
  • Layer 6 – Presentation: Data formatting, encryption, compression.
  • Layer 5 – Session: Manages sessions between applications.
  • Layer 4 – Transport: Reliable (TCP) or unreliable (UDP) data delivery; uses port numbers.
  • Layer 3 – Network: Logical addressing and routing; uses IP addresses.
  • Layer 2 – Data Link: Physical addressing (MAC addresses); Ethernet frames; switches operate here.
  • Layer 1 – Physical: Electrical signals, cables, connectors, and bit transmission.

The TCP/IP Model (4 Layers)

  • Application: Combines OSI Layers 5–7.
  • Transport: Corresponds to OSI Layer 4 (TCP, UDP).
  • Internet: Corresponds to OSI Layer 3 (IP, ICMP).
  • Network Access: Combines OSI Layers 1–2.

Key Network Devices

  • Hub: Layer 1 device; broadcasts all traffic to all ports. Largely obsolete.
  • Switch: Layer 2 device; forwards frames based on MAC address table.
  • Router: Layer 3 device; forwards packets between different networks using IP addresses.
  • Wireless Access Point (AP): Connects wireless clients to a wired LAN.

Exam Tip: Know the OSI layers by name and number, understand which devices operate at which layer, and be able to distinguish TCP from UDP (TCP is connection-oriented and reliable; UDP is connectionless and faster but unreliable).

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