Networking Fundamentals

Lesson 2 · Networking Fundamentals · Download .docx

Objectives

Explain IPv4 addressing, subnetting, and private address ranges
Differentiate TCP and UDP transport protocols
Identify the function of OSI model layers and common network devices

Key terms

IPv4: 32-bit address written in dotted-decimal notation; approximately 4.3 billion unique addresses.
CIDR: Classless Inter-Domain Routing — /24 notation specifying the number of network prefix bits.
Subnet mask: 32-bit mask defining which portion of an IP address is the network vs. host.
RFC 1918: Standard defining private IPv4 ranges: 10/8, 172.16/12, 192.168/16 — not internet-routable.
DHCP: Dynamic Host Configuration Protocol — auto-assigns IP, mask, gateway, and DNS to clients.
APIPA: 169.254.x.x self-assigned address indicating the device could not reach a DHCP server.
TCP: Transmission Control Protocol — reliable, ordered, connection-oriented transport with acknowledgments.
UDP: User Datagram Protocol — fast, connectionless, no retransmission; used for streaming and DNS.
ARP: Address Resolution Protocol — resolves an IP address to a MAC address on the local network.
Router: Layer 3 device forwarding packets between networks based on destination IP address.
Switch: Layer 2 device forwarding frames to the correct port using a MAC address table.
Hub: Layer 1 device that broadcasts all frames to every port — creates a single collision domain.

The concept

IPv4 ADDRESSING

Every device on an IP network needs a 32-bit IPv4 address, written as four decimal octets (e.g., 192.168.1.100). The address has two parts: the network portion (shared by all hosts on the same subnet) and the host portion (unique within the subnet). CIDR notation appends /24 to show that the first 24 bits are the network — leaving 8 bits for 254 usable hosts.

PRIVATE vs. PUBLIC ADDRESSES

RFC 1918 defines three private ranges — 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 — that are not routed on the public internet. Home and office networks use private addresses; NAT (Network Address Translation) on the router translates them to the single public IP the ISP assigns. When a DHCP server is unavailable, Windows self-assigns an APIPA address in 169.254.0.0/16 as a fallback.

TCP vs. UDP

TCP establishes a connection via a three-way handshake (SYN, SYN-ACK, ACK) and uses sequence numbers and acknowledgments to guarantee all packets arrive in the correct order. If a packet is lost, TCP retransmits it. UDP skips this overhead — it sends datagrams without confirmation, making it faster but unreliable. DNS queries use UDP for speed; file downloads use TCP for accuracy.

NETWORK DEVICES BY OSI LAYER

A hub operates at Layer 1 (Physical), repeating electrical signals out all ports — every device hears every frame, creating collisions. A switch operates at Layer 2 (Data Link), learning which MAC address is on each port and forwarding frames only to the correct destination. A router operates at Layer 3 (Network), reading the destination IP address in each packet and consulting its routing table to forward it toward the destination network. ARP bridges Layer 2 and Layer 3 by resolving IP addresses to MAC addresses on the local segment.

Worked examples

Example 1: A device receives the address 169.254.45.12. Diagnosis: APIPA address — the device could not reach a DHCP server. Run 'ipconfig /release' then 'ipconfig /renew'. If the problem persists, check network cable, DHCP server status, and whether the DHCP scope is exhausted.

Example 2: You need to determine whether 10.0.0.50 and 10.0.0.200 are on the same /25 subnet. A /25 subnet has a mask of 255.255.255.128. First block: 10.0.0.0–10.0.0.127. Second block: 10.0.0.128–10.0.0.255. 10.0.0.50 is in the first block; 10.0.0.200 is in the second. They are on different subnets and require a router to communicate.

Common mistakes

Confusing a switch (Layer 2, MAC addresses) with a router (Layer 3, IP addresses).
Using the broadcast address (last IP in range) or network address (first IP) as a host address.
Assuming 192.168.x.x is the only private range — 10/8 and 172.16/12 are also RFC 1918 private.
Confusing TCP with UDP — TCP is reliable but slower; UDP is fast but unreliable.
Forgetting that ARP operates on the local segment only — it cannot resolve IPs across routers.

Self-check

Try each one before you look. A miss here costs nothing and tells you exactly what to reread.

1. IPv4 addresses are how many bits?

2. An APIPA address (169.254.x.x) means:

3. Which protocol provides reliable ordered delivery with acknowledgments?

4. A switch forwards frames based on:

5. Which private IPv4 range is defined by RFC 1918?

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