Chapter 5 — Networks and the internet

Chapter 5 — Networks and the internet

Lesson map

Lesson 05 published. Map, example, EX013.

flowchart TD
  N0["Learning outcomes"]
  N1["5.1 How networks connect"]
  N2["5.2 Firewalls"]
  N3["5.3 Encryption in transit"]
  N4["5.4 Network threats"]
  N0 --> N1 --> N2 --> N3 --> N4
  N4 --> EX["Worked example"]
  EX --> Q["Exercise EX013"]

Logical drawing

flowchart LR
  N0["Learning outcomes"]
  N1["5.1 How networks connect"]
  N2["5.2 Firewalls"]
  N3["5.3 Encryption in transit"]
  N4["5.4 Network threats"]
  N0 --> N1 --> N2 --> N3 --> N4 --> Q["EX013"]

[Learning outcomes]
    |
    v
[5.1 How networks connect]
    |
    v
[5.2 Firewalls]
    |
    v
[5.3 Encryption in transit]
    |
    v
[5.4 Network threats]
    |
    v
[Worked example] --> [Exercise EX013]

Learning outcomes

You will (1) describe how networks connect computers; (2) explain firewalls and encryption in transit; (3) recognise common network threats.

5.1 How networks connect

Aisha learns that networks connect devices so they can exchange data. Ashfield's branches connect to its head office over encrypted links, and the head office connects to the internet and to the card processor. Each device has an address, and routers forward data between networks. Dr. Carrow draws the network on a whiteboard and asks students to mark where member data travel, which helps them see where protection is needed. Aisha redraws the diagram neatly at home and marks the card processor connection as the most sensitive external link.

5.2 Firewalls

A firewall controls which traffic can pass between networks. Ashfield's firewall allows web traffic to its online banking site and blocks most other incoming connections. Aisha learns that firewall rules accumulate over time and often include old exceptions nobody remembers. She reviews a synthetic rule list and finds a rule allowing remote desktop access from anywhere, created for a supplier years ago. She recommends removing it after checking with the supplier. The supplier confirms it now uses a secure remote access service instead, so the old rule is removed without disruption.

5.3 Encryption in transit

When data cross networks, others may be able to read them. Encryption in transit, such as the secure protocol used by websites, protects confidentiality and integrity along the way. Aisha checks that Ashfield's online banking uses it and that old, weak protocol versions are disabled. She learns that encryption protects data while moving, but not once they reach a compromised server, so other controls are still needed. She uses a free online checker against a test website to see which protocol versions it accepts, and records the results in her journal.

5.4 Network threats

Aisha studies common threats: attackers scanning for open services, intercepting traffic on unprotected wireless networks and overwhelming services with traffic to make them unavailable. Ashfield's branch wireless network for members is separate from staff networks, which limits risk. Dr. Carrow notes that separating networks by purpose is a simple but powerful control, because a problem in one network does not automatically reach the others. Aisha checks that the member wireless network cannot reach the staff printer, which confirms the separation works. She notes this test in her journal as an example of verifying a control rather than assuming it.

Worked example

Aisha maps Ashfield's network, finds an old open remote desktop rule, checks encryption in transit and confirms member wireless is separated.

Synthetic case. Networks are synthetic.

Errors and limits

Old firewall exceptions often stay open long after their purpose ends.

Exercises

• EX013 — Old rule. What old rule does Aisha find? Rubric: 3 = remote desktop access from anywhere;; 2 = partly correct;; 1 = other;; 0 = none.
• EX014 — Transit limits. What does encryption in transit not protect? Rubric: 3 = data on a compromised server;; 2 = partly correct;; 1 = vague;; 0 = none.
• EX015 — Member wireless. How is member wireless protected? Rubric: 3 = separated from staff networks;; 2 = partly correct;; 1 = vague;; 0 = none.

Continue studying — lesson 05 (chapter 05 of 40)

← Chapter 04 · Course chapter index · Chapter 06 →

Continue to the next authored lesson.