hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer configures IPsec on a DMVPN Phase 2…
An engineer configures IPsec on a DMVPN Phase 2 network using a transform set with ESP-AES-256-SHA. The hub and spokes are configured identically. Unexpectedly, the IPsec tunnel fails to establish, and debug output shows 'no matching crypto map entry' on the spoke. Which is the most likely explanation?
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 crypto map on the spoke uses a dynamic map, but the hub is configured with a static crypto map entry for the spoke, causing a mismatch in the IPsec negotiation.
In DMVPN, the crypto map is applied to the tunnel interface. However, if the spoke's crypto map does not match the hub's due to a missing or mismatched 'match address' access-list (interesting traffic definition), the IPsec tunnel will not initiate. The corner case is that in DMVPN, the interesting traffic is typically defined by the tunnel network itself (e.g., IPsec protects traffic between tunnel IPs). If the access-list uses the wrong source/destination, or if the crypto map is not correctly applied to the tunnel interface, the IPsec negotiation fails. Additionally, if the crypto map uses dynamic maps for the spoke, but the hub is configured with a static map, a mismatch can occur.
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 crypto map on the spoke uses a dynamic map, but the hub is configured with a static crypto map entry for the spoke, causing a mismatch in the IPsec negotiation.
Why this is correct
In DMVPN, the hub typically uses a static crypto map with multiple peers, while spokes use a dynamic crypto map to accept connections from any hub. If the spoke incorrectly uses a static map, or the hub uses a dynamic map, the negotiation fails.
- ✗
The transform set uses ESP-AES-256-SHA, but the hub is configured with ESP-AES-256-SHA-HMAC, causing a mismatch in the authentication algorithm.
Why it's wrong here
SHA and SHA-HMAC are essentially the same; this would not cause a mismatch.
- ✗
The IPsec pre-shared key is configured correctly, but the ISAKMP policy uses aggressive mode, which is incompatible with DMVPN.
Why it's wrong here
Aggressive mode can be used in DMVPN, though main mode is more common; it is not inherently incompatible.
- ✗
The spoke's tunnel interface is not in 'ip nhrp network-id' mode, causing NHRP to fail and IPsec to not trigger.
Why it's wrong here
NHRP network-id is required for DMVPN, but its absence would cause NHRP failure, not a crypto map mismatch.
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.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
Key term
DMVPN Phase 2
DMVPN Phase 2 is an advanced Cisco routing technology that allows spoke routers to communicate directly with one another without sending traffic through a central hub, using dynamic routing protocols and multipoint GRE tunnels.
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