Official exam paper
The complete exam paper for the 2025 session (BTS CIEL Option A, multi-storey car park case) is published by éduscol STI (Éducation nationale). 📄 Download the official exam paper (PDF, éduscol STI)
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The BTS CIEL E4 exam in one sentence
E4 'Computer Network Study and Design' (Option A: IT and Networks) is a 6-hour national written exam (coefficient 4). You are presented with a real-world system, here a display showing available spaces in a multi-storey car park, and asked to design, size, and secure its network infrastructure. The winning approach: think like a network engineer who builds in cybersecurity by design, not as an afterthought.
Method: design a network from sensor to service
Review the requirements and map the equipment
Before any configuration, list the equipment and data flows: parking space sensors, displays, PLC/controller, application server, operator workstations. Who communicates with whom, in which direction, and at what bandwidth? A clear flow diagram underpins everything that follows. A classic mistake is configuring before understanding the architecture.
Segment - VLANs as a security reflex
Do not put sensors, office workstations, and servers on the same flat network. Separate into VLANs by usage (field devices, servers, administration, workstations). Segmentation limits the spread of an attack and clarifies filtering rules. Justify each VLAN with a business or security need.
Define the IP addressing plan
Assign a subnet per VLAN, sized to the number of hosts (do not default to a /24 everywhere). Specify mask, gateway, any DHCP pool, and fixed IP addresses for servers and critical equipment. A coherent, documented addressing plan is a direct mark scheme point.
Choose services and protocols
Identify the required services: DHCP, DNS, inter-VLAN routing, monitoring, car park database. For each flow, choose the appropriate protocol and its secure version (HTTPS rather than HTTP, SSH rather than Telnet, SNMPv3 rather than v1/v2c). Naming the secure version is better than a vague 'I will secure it'.
Integrate cybersecurity and test
Set out the expected measures: strict inter-VLAN filtering (ACL/firewall), administrative access authentication, device hardening (passwords, disabling unnecessary services), logging. Then validate: demonstrate an allowed flow passing through and an unauthorised flow being blocked. Evidence comes before intention.
Typical marking scheme points (E4 CIEL - IR)
| Expectation | What the examiners check |
|---|---|
| Requirements analysis | Equipment and flows identified, consistent diagram |
| Segmentation / VLAN | Segmentation justified by usage and security |
| Addressing plan | Subnets properly sized, correct masks |
| Services & protocols | Appropriate choices, secure versions |
| Cybersecurity & testing | Filtering, hardening, evidence of blocked traffic |
Common mistakes
Strictly avoid
- Flat network without VLANs: a breach affects everything at once.
- Generic addressing scheme (/24 everywhere) not tailored to requirements.
- Plaintext protocols (Telnet, HTTP, SNMPv1) on sensitive access points.
- Security added at the end instead of being designed in from the start.
- No evidence: describing a measure without showing the allowed or blocked flow.