hardMultiple Choice
ISC2 CC Practice Question: Implementing a security control to prevent…
You are implementing a security control to prevent unauthorized devices from connecting to the corporate wired network. Which network access control method should be used?
⚠ Common exam trap
The trap is selecting MAC address filtering because it sounds like device control — but MAC filtering is easily spoofed and is not a real authentication mechanism, whereas 802.1X provides cryptographic, port-based admission control.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
802.1X authentication
802.1X is the IEEE standard for port-based network access control that authenticates devices and/or users before granting access to a wired or wireless LAN port. It uses EAP over LAN (EAPOL) between the supplicant and authenticator, and RADIUS between the authenticator and authentication server, providing strong, credential-based admission control. This directly addresses preventing unauthorized devices from connecting to the wired network.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
VLAN segmentation
Why it's wrong here
VLAN segmentation separates traffic into broadcast domains but does not authenticate the device before it joins a port; an unauthorised host still connects and reaches its assigned VLAN. It is tempting because segmentation limits lateral movement and would be correct for isolating guest, IoT, or server tiers once admission control has already authorised the endpoint.
- ✗
MAC address filtering
Why it's wrong here
MAC address filtering checks a spoofable layer-2 identifier that attackers can clone from an authorised device, so it cannot reliably block unauthorised hardware. It is tempting because it is simple to configure on switches and would be correct for rudimentary deterrence or inventory enforcement in a low-threat lab, not as the primary wired admission control.
- ✗
Network Access Control (NAC) only
Why it's wrong here
NAC alone authenticates and authorises endpoints, but on wired networks it typically enforces policy through 802.1X or MAC authentication bypass; without that port-level enforcement mechanism, an unauthorised device still reaches the switch. It is tempting because NAC is the umbrella discipline for admission control, and would be correct when paired with 802.1X supplicants and RADIUS.
- ✓
802.1X authentication
Why this is correct
802.1X enforces port-based authentication before granting network access, requiring devices to authenticate via a supplicant to a RADIUS server. This directly satisfies the requirement to block unauthorised devices from connecting to the corporate wired network, since unauthenticated devices are denied access at the switch port.
Quick reference
AAA Protocol Comparison
| Protocol | Port(s) | Encryption | Transport | Primary Use |
|---|---|---|---|---|
| RADIUS | 1812 / 1813 | Password only | UDP | Network access control |
| TACACS+ | 49 | Full packet | TCP | Device administration |
| Diameter | 3868 | Full session | TCP / SCTP | Carrier / mobile networks |
| 802.1X | — | EAP-based | Layer 2 | Port-based access control |
TACACS+ encrypts the entire packet; RADIUS only encrypts the password field — a key exam distinction.
Go deeper
Related to this question
Learn chapter
Secure Network Architecture and Design
Key term
EAPoL
EAPoL is a network authentication protocol that encapsulates EAP frames over IEEE 802 LANs, enabling port-based access control.
Key term
Authentication
Authentication is the process of verifying that someone or something is who or what it claims to be before granting access to a system or resource.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official ISC2 exam blueprint
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