Notes — Module 01: Introduction to Computer Networks¶

These are your personal study notes. Write freely and honestly. Incomplete notes are fine — they show where your understanding still needs work. Return to this file to add insights as they develop over time.

Module: [[networks/modules/01_introduction]] Topic: [[networks]] Date started: To be filled in Status: Not started

Concept Map¶

Sketch how the concepts in this module relate to each other. Fill in the Mermaid diagram.

mindmap
  root((Networks Intro))
    Network Models
      OSI 7 Layers
      TCP/IP 4 Layers
      Layer Mapping
    Topologies
      Bus
      Ring
      Star
      Mesh
    Data Travel
      Encapsulation
      Frames vs Packets
      MAC vs IP
    Devices
      Hub vs Switch
      Router
      Firewall
    Tools
      ping
      traceroute
      netstat / ss

Alternative: draw this on paper, photo it, and link the image here.

Key Insights¶

The "aha moments" — the things that, once understood, made the rest clear. Be specific: "I finally understood X because Y" is more useful than "X makes sense".

Encapsulation analogy: To be filled in
Why MAC addresses are local: To be filled in
Add insights as you discover them

My Understanding¶

Explain the core concepts in your own words, as if teaching them to someone else. If you can't explain it simply, you don't understand it well enough yet.

The OSI Model¶

Your explanation here

What I'm still unsure about: To be filled in

Encapsulation¶

Your explanation here

What I'm still unsure about: To be filled in

The difference between a switch and a router¶

Your explanation here

Connections to Other Topics¶

How does this module connect to things you already know?

This module's concept	Connects to	How
Layered abstraction	[[systems-architecture]]	Same principle of separation of concerns applies to software architecture
Protocol design	[[pentesting-security]]	Attacks exploit specific protocol weaknesses at specific layers
Network devices	[[devops-platform-engineering]]	Cloud VPCs, security groups, and load balancers map to OSI layers

Questions That Arose¶

Log questions as they appear. Don't stop to answer them now — just capture them. Then move the serious ones to QUESTIONS.md.

Question 1 → add to QUESTIONS.md
Question 2 → needs more study
Question 3 → might be answered later in the module

Code Snippets Worth Remembering¶

Reading the traceroute output¶

# traceroute output shows: hop number, IP address of the router, RTT x3
# *** means no ICMP response (firewall blocking) — not necessarily an outage
traceroute google.com
#  1  192.168.1.1      1.2 ms  1.1 ms  1.2 ms   (home router)
#  2  10.0.0.1         8.5 ms  8.3 ms  8.6 ms   (ISP hop)
#  3  * * *                                      (blocked ICMP)
#  4  142.250.80.46   12.3 ms  12.1 ms  12.4 ms (destination)

Why I'm saving this: the *** behavior trips people up — it doesn't mean the route is broken.

Checking what's listening on a port¶

# Find what process is listening on port 80
ss -tulnp | grep :80

# Or check all TCP listeners
ss -tlnp

Why I'm saving this: useful for debugging "something is already using port 80" errors.

What Tripped Me Up¶

Mistakes I made, misconceptions I had, things that confused me more than they should have. Being honest here helps you later.

Expecting OSI layers to map directly to software layers: To be filled in
Thinking MAC addresses are globally routable: To be filled in

Summary in My Own Words¶

Write a 3–5 sentence summary of this entire module without looking at any notes. If you can't do this, you need more study time.

To be filled in after completing the module.

Last updated: _To be filled in_