350-701 Practice Question: Secure Network Access, Visibility and Enforcement
A network administrator is configuring 802.1X for wired access on a Cisco switch. The switch is configured for RADIUS using a Cisco ISE server. During testing, a client that supports 802.1X is unable to authenticate and fails to gain network access. The administrator checks the switch logs and sees "Authentication failed: invalid EAP code received". What is the most likely cause?
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
✓
The client is using an unsupported EAP method (e.g., EAP-TLS instead of PEAP).
The error 'invalid EAP code received' indicates that the switch received an EAP packet with a code it does not support, which typically occurs when the client uses an unsupported EAP method. Option A is correct because if the client attempts a method like EAP-TLS while the switch or RADIUS server expects PEAP, the EAP code may be unrecognized. Option B is wrong because RADIUS unreachability would result in timeouts or 'no response' errors, not EAP code errors. Option C is wrong because a shared secret mismatch would cause RADIUS authentication rejections (e.g., 'Access-Reject'), not EAP parsing issues. Option D is wrong because a trunk port configuration would cause VLAN mismatches or connectivity issues, not EAP code errors.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The client is using an unsupported EAP method (e.g., EAP-TLS instead of PEAP).
Why this is correct
The switch cannot process an unrecognized EAP code, which occurs when the client negotiates an unsupported method.
- ✗
The RADIUS server is unreachable.
Why it's wrong here
Unreachable RADIUS server results in timeouts or no response, not an invalid EAP code from the switch.
- ✗
The switch is configured with the wrong shared secret for RADIUS.
Why it's wrong here
Shared secret mismatch results in RADIUS authentication failures with different error messages, not EAP code errors.
- ✗
The switch port is configured as a trunk port rather than an access port.
Why it's wrong here
Trunk port configuration would cause VLAN tagging mismatch, not an EAP code error at the authentication layer.
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.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-701 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 350-701 exam.