Chapter 11 — Networks and protocols
Lesson map
Lesson 11 published. Map, example, EX031.
flowchart TD
N0["Learning outcomes"]
N1["11.1 Mapping zones"]
N2["11.2 What protocols protect"]
N3["11.3 Weaknesses of flat networks"]
N4["Synthesis"]
N0 --> N1 --> N2 --> N3 --> N4
N4 --> EX["Worked example"]
EX --> Q["Exercise EX031"]
Logical drawing
flowchart LR
N0["Learning outcomes"]
N1["11.1 Mapping zones"]
N2["11.2 What protocols protect"]
N3["11.3 Weaknesses of flat networks"]
N4["Synthesis"]
N0 --> N1 --> N2 --> N3 --> N4 --> Q["EX031"]
[Learning outcomes]
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v
[11.1 Mapping zones]
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v
[11.2 What protocols protect]
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v
[11.3 Weaknesses of flat networks]
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v
[Synthesis]
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v
[Worked example] --> [Exercise EX031]
Learning outcomes
You will (1) map Corvia's network zones and protocols; (2) explain what TLS, VPNs and segmentation protect; (3) identify architectural weaknesses in a flat network.
11.1 Mapping zones
Sofia draws Corvia's network: buses and trams connect over cellular links to a depot gateway; depots connect to the central data centre; the passenger app and website sit in a cloud environment; corporate offices have their own network. Each zone has different users, devices and threats. She lists the protocols crossing each boundary, such as HTTPS for the app, a VPN from vehicles to depots and a vendor's proprietary protocol for fare validators. A map like this is the starting point for every architecture review, because protections must be placed where traffic crosses trust boundaries.
11.2 What protocols protect
TLS, specified in RFC 8446, protects data in transit between two endpoints with encryption, integrity and server authentication. A VPN creates an encrypted tunnel between networks, so vehicle traffic crossing public cellular networks is protected. Neither controls what happens inside an endpoint or which internal systems a connected device may reach. Segmentation does that, by limiting which zones can talk to which. Sofia notes that a VPN which drops every bus straight into the central network without filtering would protect confidentiality on the cellular link but give a compromised bus a path to everything.
11.3 Weaknesses of flat networks
In Corvia's older depot, staff laptops, fare servers and printers share one network segment. Sofia explains the risk to Daniel: one infected laptop can reach fare servers directly, and monitoring cannot easily tell normal from abnormal traffic when everything talks to everything. Anderson (2020) describes incidents where flat internal networks let attackers move freely. She proposes separating zones with firewalls and allowing only required flows, the approach later formalised in zero trust guidance such as SP 800-207, and lists the flows each zone legitimately needs as the basis for rules.
Worked example
Sofia maps six Corvia zones and their boundary protocols, explains the limits of VPN tunnels and proposes segmenting the flat depot network by required flows.
Synthetic case. Zones and flows are synthetic; RFC 8446, SP 800-207 and Anderson (2020) are real.
Errors and limits
Network maps go stale quickly. Segmentation rules must be maintained or they drift back toward flat.
Exercises
- EX031 — VPN limit. What does a vehicle VPN not control? Rubric: 3 = which internal systems the connected device can reach;; 2 = reach;; 1 = confidentiality;; 0 = none.
- EX032 — Flat depot risk. Name two problems with the flat depot network. Rubric: 3 = infected laptop reaches fare servers; monitoring cannot separate normal from abnormal;; 2 = two;; 1 = one;; 0 = none.
- EX033 — Rule basis. What should segmentation rules be based on? Rubric: 3 = the flows each zone legitimately needs;; 2 = required flows;; 1 = all flows;; 0 = none.
Synthesis
Network architecture places protocols and segmentation where traffic crosses trust boundaries, not only where it crosses the internet.
Continue studying — chapter 11 of 50
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