Notes · Summary

Network models summary

Page 4 of 4

A tight recap of OSI and TCP IP with a practice checklist.

Summary

This page is a recap. It is designed to be short.

CPD and certification alignment (guidance, not endorsed):

This recap supports the foundations expected in networking pathways such as:

  • CompTIA Network+ (baseline networking terms and troubleshooting)
  • Cisco CCNA (core behaviour, protocols, and practical diagnosis)
How to use this recap
Read it once, then use it during real troubleshooting. That is when it becomes valuable.
Good practice
Write one sentence that describes the failure at a specific layer, then write one test that could disprove you. That stops guessing.
Bad practice
Best practice

The smallest set of terms that must be correct

  1. A protocol is a set of rules for exchanging data.
  2. Encapsulation wraps data with headers as it moves down the stack.
  3. A frame carries a packet. A packet carries a segment or datagram.
  4. DNS maps names to records such as IP addresses.
  5. TLS protects data in transit. It does not make the application safe by itself.
Common misconceptions I correct
Misconception: TCP is reliable so the network is fine
TCP can hide loss until it cannot. A system can be “working” and still be unusable because latency and retransmissions exploded.
Misconception: TLS means secure
Misconception: DNS is only names

A troubleshooting checklist you can reuse

  1. State the symptom.
  2. State what success looks like.
  3. Test one boundary at a time.
  4. Record evidence.
  5. Keep assumptions explicit.

If you are stuck, do not jump layers. Prove the lower layers first, then move up.

CPD evidence prompt (copy friendly)

What I studied: OSI and TCP/IP terms, encapsulation, DNS, TLS, and a disciplined troubleshooting sequence. What I practised: one real troubleshooting loop with evidence and an explicit assumption list. Evidence artefact: a short incident note that links symptom, evidence, layer, and fix.

Quick check

Scenario: You watch a request move down the stack and each layer adds its own fields. What is the correct term for this behaviour

Scenario: DNS works and you can reach the local network, but the destination network is unreachable. What does routing actually decide

Scenario: TLS is enabled and the padlock shows. A user still gets their data exposed to another account. What did TLS not protect you from

Support

If these notes or games help you, a small donation keeps the site independent and well tested.

Quick feedback

Optional. This helps improve accuracy and usefulness. No accounts required.