Question 831 of 2,152

DMVPN →hardMultiple ChoiceObjective-mapped

IPsec Crypto Map Mismatch on DMVPN Spoke — No Matching Entry | Cisco CCNP ENARSI 300-410 Explained

This 300-410 practice question tests your understanding of dmvpn. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

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?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
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 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.
B
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 wrong: SHA and SHA-HMAC are essentially the same; this would not cause a mismatch.
C
The IPsec pre-shared key is configured correctly, but the ISAKMP policy uses aggressive mode, which is incompatible with DMVPN.
Why wrong: Aggressive mode can be used in DMVPN, though main mode is more common; it is not inherently incompatible.
D
The spoke's tunnel interface is not in 'ip nhrp network-id' mode, causing NHRP to fail and IPsec to not trigger.
Why wrong: NHRP network-id is required for DMVPN, but its absence would cause NHRP failure, not a crypto map mismatch.

Full breakdown with real-world context →

Quick Answer

The answer is a mismatch between the spoke’s dynamic crypto map and the hub’s static crypto map entry for the spoke. In a DMVPN Phase 2 network, the hub typically uses a static crypto map with a specific peer address and an access-list defining interesting traffic, while the spoke often relies on a dynamic crypto map to accept connections from multiple peers. When the spoke’s crypto map is dynamic but the hub’s static map does not include a matching entry for that spoke, IPsec negotiation fails with the ‘no matching crypto map entry’ error, even if transform sets like ESP-AES-256-SHA are identical. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how DMVPN crypto maps must align between hub and spoke—a common trap is assuming identical transform sets guarantee success, while the real issue lies in the map type or the ‘match address’ access-list defining the tunnel network as interesting traffic. Remember the mnemonic: “Static hub, dynamic spoke—if the map type’s broke, the tunnel’s a joke.”

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.

Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

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.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
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.

Common exam traps

Common exam trap: ACLs stop at the first match

ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.

Detailed technical explanation

How to think about this question

ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.

KKey Concepts to Remember

Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.

TExam Day Tips

Check inbound versus outbound direction.
Read the ACL from top to bottom.
Look for a broader permit or deny above the intended line.

Key takeaway

ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

Real-world example

How this comes up in practice

A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

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.

What to study next

Got this wrong? Here's your next step.

Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 300-410 ACL questions on filtering logic and placement.

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FAQ

Questions learners often ask

What does this 300-410 question test?

DMVPN — This question tests DMVPN — Standard ACLs match source addresses..

What is the correct answer to this question?

The correct answer is: 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.

What should I do if I get this 300-410 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Standard ACLs match source addresses.

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