350-601 Security Practice Question
Two data center switches are connected via a fiber link. They need to encrypt all traffic at Layer 2. Which configuration is required on both switches to establish MACsec?
⚠ Common exam trap
Cisco often tests the distinction between Layer 2 encryption (MACsec) and Layer 3 encryption (IPsec), and candidates mistakenly choose IPsec because they associate 'encryption' with IPsec, forgetting that MACsec is the correct solution for Layer 2 traffic.
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
✓
Enable MACsec and configure a pre-shared key or CA
MACsec (IEEE 802.1AE) provides hop-by-hop Layer 2 encryption between directly connected switches. To establish a MACsec session, both switches must enable MACsec on the interface and either configure a pre-shared key (PSK) or use a CA (Connectivity Association) key agreement protocol like MKA (MACsec Key Agreement, IEEE 802.1X-2010). This ensures all Ethernet frames are encrypted at the data link layer.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure the interface as a trunk
Why it's wrong here
Trunking allows multiple VLANs but does not provide encryption.
- ✓
Enable MACsec and configure a pre-shared key or CA
Why this is correct
MACsec must be enabled and a security key configured (PSK or CA) to establish secure links.
- ✗
Enable IPsec on the interface
Why it's wrong here
IPsec is Layer 3 encryption, not Layer 2.
- ✗
Enable 802.1X on the interface
Why it's wrong here
802.1X is for network access control, not encryption; MACsec uses MKA which can be independent.
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
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