Question 1,155 of 1,389
CCNA Network Services and Security Practice Question
Which TWO statements correctly describe the differences between RADIUS and TACACS+ when configuring AAA on IOS-XE?
⚠ Common exam trap
Cisco often tests the encryption behavior (Option A) as a trap, because candidates confuse which protocol encrypts the entire packet versus just the password, and they also test the authorization granularity (Option C) to see if you know that TACACS+ supports command-level authorization while RADIUS does not.
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
✓
TACACS+ uses TCP port 49, while RADIUS uses UDP ports 1812 and 1813.
Options B and D are correct. TACACS+ uses TCP port 49, while RADIUS uses UDP ports 1812 (authentication) and 1813 (accounting). TACACS+ separates authentication, authorization, and accounting into three distinct processes, whereas RADIUS combines authentication and authorization. Option A is incorrect because TACACS+ encrypts the entire packet body, while RADIUS encrypts only the password. Option C is incorrect because TACACS+ supports command-level authorization, while RADIUS does not. Option E is incorrect because 802.1X port-based authentication uses RADIUS, not TACACS+.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
RADIUS encrypts the entire packet body, while TACACS+ encrypts only the password.
Why it's wrong here
This statement is reversed: RADIUS encrypts only the password, while TACACS+ encrypts the entire packet body (except the header).
- ✓
TACACS+ uses TCP port 49, while RADIUS uses UDP ports 1812 and 1813.
Why this is correct
TACACS+ uses TCP for reliable transport on port 49, while RADIUS uses UDP (port 1812 for authentication/authorization, 1813 for accounting).
- ✗
RADIUS supports command-level authorization, whereas TACACS+ does not.
Why it's wrong here
TACACS+ supports per-command authorization (via the 'aaa authorization commands' feature), while RADIUS does not have native command-level authorization.
- ✓
TACACS+ separates authentication, authorization, and accounting into distinct processes, while RADIUS combines authentication and authorization.
Why this is correct
TACACS+ uses separate AAA processes (each with its own packet type), allowing granular control. RADIUS combines authentication and authorization in the same Access-Request/Access-Accept exchange.
- ✗
Both RADIUS and TACACS+ can be used for 802.1X port-based authentication on IOS-XE.
Why it's wrong here
Both RADIUS and TACACS+ can serve as AAA servers for 802.1X authentication on IOS-XE switches. However, RADIUS is more commonly used with 802.1X because of its native support for EAP.
When this WOULD be correct
This is correct because both protocols are supported for 802.1X, though RADIUS is the typical choice.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓TACACS+ uses TCP port 49, while RADIUS uses UDP ports 1812 and 1813.Correct answer▾
Why this is correct
TACACS+ uses TCP for reliable transport on port 49, while RADIUS uses UDP (port 1812 for authentication/authorization, 1813 for accounting).
✗RADIUS encrypts the entire packet body, while TACACS+ encrypts only the password.Wrong answer — click to see why▾
Why this is wrong here
The encryption behavior is opposite to what is described.
✗RADIUS supports command-level authorization, whereas TACACS+ does not.Wrong answer — click to see why▾
Why this is wrong here
The statement reverses the capability: TACACS+ supports command authorization, not RADIUS.
✗Both RADIUS and TACACS+ can be used for 802.1X port-based authentication on IOS-XE.Wrong answer — click to see why▾
Why this is wrong here
Both RADIUS and TACACS+ can serve as AAA servers for 802.1X authentication on IOS-XE switches. However, RADIUS is more commonly used with 802.1X because of its native support for EAP.
★ When this WOULD be the correct answer
This is correct because both protocols are supported for 802.1X, though RADIUS is the typical choice.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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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Last reviewed: Jun 11, 2026
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