Chapter 2 — Networks and internet services
Lesson map
Lesson 02 published. Map, example, EX004.
flowchart TD
N0["Learning outcomes"]
N1["2.1 Addresses, ports and protocols"]
N2["2.2 How nodes communicate"]
N3["2.3 Securing exposed services"]
N4["Synthesis"]
N0 --> N1 --> N2 --> N3 --> N4
N4 --> EX["Worked example"]
EX --> Q["Exercise EX004"]
Logical drawing
flowchart LR
N0["Learning outcomes"]
N1["2.1 Addresses, ports and protocols"]
N2["2.2 How nodes communicate"]
N3["2.3 Securing exposed services"]
N4["Synthesis"]
N0 --> N1 --> N2 --> N3 --> N4 --> Q["EX004"]
[Learning outcomes]
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v
[2.1 Addresses, ports and protocols]
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v
[2.2 How nodes communicate]
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v
[2.3 Securing exposed services]
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v
[Synthesis]
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v
[Worked example] --> [Exercise EX004]
Learning outcomes
You will (1) explain addresses, ports and protocols; (2) describe how nodes talk to each other; (3) secure exposed services.
2.1 Addresses, ports and protocols
Every device on a network has an address, and each service on it listens on a port. Protocols define how messages are formatted and exchanged. Lucas maps the makerspace's network: the three node servers, the booking web application, members' devices and the office router. He lists which ports each node uses for peer connections and for its programming interface, which the booking application uses to read balances and submit transactions. Knowing addresses and ports lets him check what is reachable from where, which is the basis of network security and of fault finding.
2.2 How nodes communicate
Nodes exchange blocks and transactions with peers over the internet. On the makerspace's permissioned ledger, each node is configured with an allow-list of the other two nodes and refuses others. The booking application talks to one node's programming interface. Lucas traces a booking: a member's wallet signs a transaction, the booking application sends it to a node, the node shares it with peers, the next block includes it and the application confirms the booking. Each hop is a place where delays or failures can occur, and each needs monitoring to show where a slow booking is held up.
2.3 Securing exposed services
The node programming interface can submit transactions and read data, so it must not be open to the whole internet. Lucas checks and finds that one node's interface is reachable from outside the rack. He reports it, and the firewall is changed so only the booking application server can reach it. He also confirms that administrative access requires keys, not passwords. NIST IR 8202 notes that permissioned networks depend on controlling who can participate and connect. Restricting exposed services is one of the simplest and most effective controls a technologist can apply on day one.
Worked example
Lucas finds one node's programming interface reachable from the internet and has the firewall limit it to the booking server.
Synthetic case. The network and findings are synthetic; NIST IR 8202 is a real source.
Errors and limits
Leaving a node's programming interface open to the internet exposes functions meant only for trusted applications.
Exercises
- EX004 — Interface user. Which application uses a node's programming interface? Rubric: 3 = the booking web application;; 2 = booking app;; 1 = members' phones directly;; 0 = none.
- EX005 — Booking path. Name one hop in a booking's journey. Rubric: 3 = node shares with peers;; 2 = wallet signs;; 1 = email;; 0 = none.
- EX006 — Exposure fix. How was the exposed interface fixed? Rubric: 3 = firewall limited it to the booking server;; 2 = firewall;; 1 = removed node;; 0 = none.
Synthesis
Mapping addresses and ports and restricting exposed services secure node communication.
Continue studying — chapter 02 of 30
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