CCNP Infrastructure Practice Question
A network administrator is configuring a Cisco Catalyst 9000 switch to authenticate users via 802.1X. The authentication server is a Cisco Identity Services Engine (ISE). The administrator wants to ensure that if the ISE server becomes unreachable, the switch will allow devices to connect with limited access. Which feature should be configured?
⚠ Common exam trap
A common mix-up: candidates confuse Guest VLAN with Critical VLAN or Inaccessible Authentication Bypass; Guest VLAN is for non-802.1X devices, while IAB is for server unreachability.
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
✓
Inaccessible Authentication Bypass
Inaccessible Authentication Bypass is designed to handle the situation where the RADIUS server is unreachable. It allows the switch to apply a preconfigured access policy, often assigning the port to a critical VLAN, ensuring that devices can still connect with limited access. This meets the requirement of maintaining connectivity during server outages.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
MAC Authentication Bypass
Why it's wrong here
MAC Authentication Bypass (MAB) is used for devices that do not support 802.1X supplicant. It uses the device's MAC address as credentials. It does not address the scenario of the authentication server being unreachable; it is a fallback method for non-802.1X devices.
- ✗
Critical VLAN
Why it's wrong here
Critical VLAN is used when the authentication server is unreachable, but it typically provides limited access. However, the question specifies 'limited access', which is more aligned with a guest VLAN or restricted VLAN. Critical VLAN is often used for critical devices that need access even when ISE is down, but it may not provide limited access; it often provides full access or specific access based on configuration.
- ✓
Inaccessible Authentication Bypass
Why this is correct
Inaccessible Authentication Bypass (IAB) allows a port to grant access when the authentication server is unreachable. It can be configured to assign the port to a critical VLAN or apply a specific policy. This matches the requirement to allow devices to connect with limited access when ISE is down.
- ✗
Guest VLAN
Why it's wrong here
Guest VLAN is used when a device does not support 802.1X or fails authentication, not when the authentication server is unreachable. It provides limited access for guests. The scenario specifies the server becoming unreachable, which is handled by critical VLAN or inaccessible authentication bypass, not guest VLAN.
Visual reference
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.
About these practice questions
This 350-401 question is part of Courseiva's 1,923-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
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 Cisco exam blueprint
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.