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350-701 Practice Question: Is trying to establish a site-to-site IPsec VPN…
A network engineer is trying to establish a site-to-site IPsec VPN between two Cisco routers. The IKEv2 proposal uses AES-256 encryption and SHA-256 hash. On the remote router, the configuration shows only AES-128 and SHA-1. What will happen during IKEv2 negotiation?
⚠ Common exam trap
Cisco often tests the misconception that IKEv2 will automatically negotiate a 'best common' set of parameters or fall back to IKEv1, when in fact it requires an exact match on the entire proposal and has no backward compatibility with IKEv1.
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 IKEv2 negotiation will fail because no common proposal exists.
IKEv2 negotiation requires that both peers have at least one matching proposal (encryption, hash, DH group, etc.) in their configured transform sets. Since the local router offers AES-256/SHA-256 and the remote router only offers AES-128/SHA-1, there is no common proposal. IKEv2 does not perform automatic fallback or mixing of parameters; it simply fails if no match is found.
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 router with stronger proposal will override the other.
Why it's wrong here
No overriding; they must match exactly on an offered proposal.
- ✓
The IKEv2 negotiation will fail because no common proposal exists.
Why this is correct
Both sides must have at least one matching proposal for IKEv2 to establish.
- ✗
The routers will automatically fall back to IKEv1.
Why it's wrong here
IKEv2 and IKEv1 are different protocols; no automatic fallback.
- ✗
The routers will negotiate and use AES-128 with SHA-256.
Why it's wrong here
IKEv2 picks a match from each side's proposals; they must share a common proposal.
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 350-701 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 350-701 exam.