Networking Fundamentals

Week of 2026-09-08 · Download .docx

Objectives

Explain IPv4 addressing, subnetting basics, DHCP, and private vs. public address ranges.
Identify network hardware including hubs, switches, routers, WAPs, and cabling.
Describe the OSI model's seven layers and map protocols to their correct layers.
Identify common protocols and their port numbers including SSH, DNS, HTTPS, and RDP.

Key terms

OSI model: Seven-layer reference framework: Physical, Data Link, Network, Transport, Session, Presentation, Application.
IP address: 32-bit (IPv4) or 128-bit (IPv6) numeric label assigned to each network interface.
Subnet mask: Defines which bits of an IP address identify the network versus the host.
DHCP: Dynamic Host Configuration Protocol — automatically assigns IP address, mask, gateway, and DNS server.
APIPA: Automatic Private IP Addressing — self-assigned 169.254.x.x when DHCP is unreachable.
Default gateway: The router's IP on the local subnet; all traffic destined for other networks is sent here.
DNS: Domain Name System — translates human-readable hostnames to IP addresses; port 53.
Switch: Layer 2 device that learns MAC addresses and forwards frames only to the correct port.
Router: Layer 3 device that routes IP packets between different networks using a routing table.
WAP: Wireless Access Point — broadcasts an SSID over 802.11 radio to connect Wi-Fi clients.
TCP: Transmission Control Protocol — reliable, ordered, acknowledged delivery using a three-way handshake.
UDP: User Datagram Protocol — connectionless, no acknowledgment; faster but unreliable.
ARP: Address Resolution Protocol — resolves a known IP address to its corresponding MAC address.
SSH: Secure Shell — encrypted remote CLI access; TCP port 22.
RDP: Remote Desktop Protocol — graphical remote desktop for Windows; TCP port 3389.

The concept

Networking allows computers and devices to communicate, share resources, and access the internet. The OSI (Open Systems Interconnection) model provides a seven-layer framework for understanding how data travels from application to wire. Each layer wraps the data with a header — a process called encapsulation — and the receiving device strips headers back up the stack.

IPv4 addresses are 32-bit numbers written in dotted decimal (e.g., 192.168.1.100). A subnet mask defines the boundary between the network portion and host portion of an address. CIDR notation expresses this as a prefix length: /24 means 24 network bits, leaving 8 host bits (254 usable addresses). The RFC 1918 private ranges — 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 — are not routed on the public internet and are safe to use internally. IPv6 expands to 128 bits in hexadecimal groups to solve IPv4 address exhaustion.

DHCP simplifies network administration by automatically providing four settings to every client: IP address, subnet mask, default gateway, and DNS server. If a device cannot reach a DHCP server, Windows assigns an APIPA address (169.254.x.x) as a fallback. The loopback address 127.0.0.1 always refers to the local machine's TCP/IP stack — pinging it confirms software configuration is correct without testing any cable.

Layer 1 (Physical) handles bits on wire: cables, connectors, voltages. A hub operates here — it broadcasts every frame to every port. Layer 2 (Data Link) introduces MAC addresses and framing. Switches learn which device is connected to each port and forward frames to the correct destination. Layer 3 (Network) handles IP routing between different networks — routers make forwarding decisions here. Layer 4 (Transport) manages TCP and UDP end-to-end delivery with port numbers.

Common protocols and their ports: HTTP (80), HTTPS (443), DNS (53), SSH (22), FTP (21), SMTP (25), IMAP (143), RDP (3389), Telnet (23). ARP resolves IP addresses to MAC addresses on the local subnet. Ping uses ICMP to test reachability and measure round-trip time. HTTPS wraps HTTP over TLS, encrypting traffic between browser and server so eavesdroppers cannot read it.

Worked examples

Example 1: A user's PC shows a 169.254.12.55 IP address and cannot access the network. You run ipconfig and confirm the APIPA address. You ping the default gateway — timeout. You check the network cable — the switch port's link light is off. You reseat the cable; the link light goes green, DHCP assigns a proper 192.168.1.x address, and network access is restored.

Example 2: You need to find out whether a server (10.10.1.50) is reachable and whether DNS can resolve its hostname. First you ping 127.0.0.1 (loopback passes — TCP/IP stack OK). Then ping 192.168.1.1 (gateway passes — local routing OK). Then ping 10.10.1.50 (passes — IP reachable). Then ping server01.corp.local (fails — DNS failure). You run nslookup server01.corp.local and see it queries the wrong DNS server. You correct the DNS setting and resolve the issue.

Common mistakes

Confusing a switch (Layer 2, MAC addresses) with a router (Layer 3, IP addresses) — they operate at different OSI layers.
Assuming 169.254.x.x is a valid network address — it always means DHCP failed.
Mixing up TCP and UDP — if reliability and ordering matter, use TCP; if speed matters more (video, DNS queries), UDP is used.
Forgetting that DNS uses both UDP (queries) and TCP (zone transfers, large responses) on port 53.
Pinging a hostname to test connectivity and concluding the network is down when it is really just DNS that is broken.

Self-check

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

1. What layer of the OSI model does a router operate at?

2. What does a 169.254.x.x IP address indicate?

3. Which port does SSH use?

4. ARP resolves which type of address?

5. Which protocol provides reliable, ordered delivery with acknowledgments?

Canvas is the official record. This companion enhances the PGCC curriculum; it does not replace it. Last name and class year only. Students with a 504 plan or IEP: your accommodations apply.

↑ Back to top