hardMultiple ChoiceObjective-mapped
300-410 Practice Question: Configures SNMPv3 with authentication and privacy…
A network engineer configures SNMPv3 with authentication and privacy on a router. The NMS polls the router successfully. The engineer then configures IPsec to encrypt all traffic between the router and the NMS. The NMS now fails to poll the router. Which is the most likely explanation?
⚠ Common exam trap
Cisco often tests the misconception that IPsec automatically encrypts all traffic on an interface, when in fact it requires an explicit ACL to match the desired traffic, and candidates may overlook the need to include SNMP (UDP 161) in that ACL.
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 IPsec configuration does not include an ACL that matches SNMP traffic (UDP port 161).
When IPsec is configured to encrypt traffic between the router and the NMS, it must explicitly match the SNMP traffic using an access control list (ACL) that permits UDP port 161. Without this ACL, the IPsec policy does not recognize SNMP packets as interesting traffic and does not apply encryption, but more critically, the IPsec security association (SA) may not be established for SNMP packets, causing them to be dropped or not processed correctly. The NMS fails to poll because the SNMP requests are not being encrypted/decrypted as expected, breaking communication.
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 IPsec configuration does not include an ACL that matches SNMP traffic (UDP port 161).
Why this is correct
If the IPsec crypto map's ACL does not match SNMP packets, the traffic is sent in clear text, but the NMS may expect encrypted traffic or the router may not process the packets correctly.
- ✗
SNMPv3 encryption and IPsec encryption are incompatible and cannot be used together.
Why it's wrong here
They can be used together, but it is redundant.
- ✗
The IPsec configuration uses aggressive mode, which is incompatible with SNMPv3.
Why it's wrong here
IPsec mode does not affect SNMPv3 compatibility.
- ✗
The router's SNMP process must be restarted after IPsec is configured.
Why it's wrong here
No restart is required.
Visual reference
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
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JA
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.