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300-410 Practice Question: Is troubleshooting a Cisco router that is…
A network engineer is troubleshooting a Cisco router that is configured for TACACS+ authentication. The engineer issues 'test aaa group tacacs+ admin cisco123 new-code' and receives 'FAILED'. The router can ping the TACACS+ server. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the distinction between Layer 3 reachability (ping) and Layer 4 connectivity (TCP port 49), trapping candidates who assume that successful ping implies full connectivity to the TACACS+ server.
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
✓
TCP port 49 is blocked between the router and the TACACS+ server.
The 'test aaa group tacacs+ admin cisco123 new-code' command uses the 'new-code' flag, which forces the test to use the TACACS+ protocol (TCP port 49) rather than the older, less secure method. Since the router can ping the TACACS+ server, Layer 3 connectivity is fine, but a failed authentication with 'new-code' strongly indicates that TCP port 49 is blocked by a firewall or ACL between the router and the server. TACACS+ relies on TCP port 49 for all communication, so blocking this port causes immediate failure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
TCP port 49 is blocked between the router and the TACACS+ server.
Why this is correct
Correct because TACACS+ uses TCP port 49; if blocked, the router cannot establish a connection to the server.
- ✗
The TACACS+ server shared key is incorrect.
Why it's wrong here
Incorrect because if the shared key were incorrect, the server would respond with a reject, not a failure due to timeout.
- ✗
The username 'admin' does not exist on the TACACS+ server.
Why it's wrong here
Incorrect because the test command would still receive a response from the server indicating authentication failure.
- ✗
The TACACS+ server is not configured for the router's IP address.
Why it's wrong here
Incorrect because the server would still respond with a reject if the client is not authorized.
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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 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 300-410 exam.