ANS-C01 Network Implementation Practice Question
A network engineer is troubleshooting connectivity between an on-premises data center and a VPC over an AWS Site-to-Site VPN. The tunnel status shows UP, but traffic from on-premises to the VPC is intermittently dropped. Which TWO of the following are likely causes? (Choose 2.)
⚠ Common exam trap
The trap here is that candidates often focus on tunnel status (UP) and assume the issue must be related to IPsec parameters or BGP timers, overlooking the subtle but common problem of asymmetric routing causing stateful firewall drops.
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
✓
Asymmetric routing across multiple tunnels
Asymmetric routing across multiple tunnels can cause intermittent drops because traffic from on-premises to the VPC may take one tunnel, while return traffic takes a different tunnel. If the stateful firewall (e.g., security groups, network ACLs, or on-premises firewall) sees packets from a different source IP or interface than expected, it may drop the return packets, leading to connectivity issues even though both tunnels are UP.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Dead Peer Detection (DPD) timeout configuration
Why it's wrong here
DPD timeout would bring the tunnel down, not cause intermittent drops.
- ✗
BGP hold timer expiration
Why it's wrong here
Hold timer expiration resets BGP session, not intermittent drops.
- ✓
Asymmetric routing across multiple tunnels
Why this is correct
Asymmetric routing can cause stateful devices to drop packets.
- ✓
Incorrect MTU size causing packet fragmentation
Why this is correct
MTU mismatch leads to fragmentation and potential drops.
- ✗
IPsec SA lifetime mismatch between peers
Why it's wrong here
SA mismatch causes rekey failures, not typical intermittent drops.
Quick reference
Asymmetric Encryption Algorithm Comparison
| Algorithm | Key Exchange | Signatures | Equivalent Security Key | Notes |
|---|---|---|---|---|
| RSA-3072 | Yes | Yes | 128-bit | Widely deployed; slow for bulk data |
| ECDSA P-256 | No | Yes | 128-bit | Fast signatures; standard TLS certs |
| ECDH / ECDHE | Yes | No | 128-bit | Perfect forward secrecy in TLS 1.3 |
| DH / DHE | Yes | No | 128-bit (3072-bit key) | Replaced by ECDHE in modern TLS |
| Ed25519 | No | Yes | ~128-bit | SSH keys, modern PKI |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services 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 ANS-C01 exam.