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IPsec Site-to-Site VPN →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the debug crypto isakmp output indicates a proposal mismatch, specifically that the ISAKMP transform set attributes—encryption DES-CBC, hash SHA, and DH group 2—sent by the peer at 192.168.1.2 were rejected because they did not match any configured ISAKMP policy on the local router. This is confirmed by the lines “atts are not acceptable” and “no offers accepted,” which show the router compared the peer’s proposal against its own priority 1 policy and found no compatible combination of encryption, hash, authentication, or Diffie-Hellman group. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your ability to interpret Phase 1 negotiation failures, a common troubleshooting trap where candidates overlook that both peers must share identical ISAKMP policy parameters (e.g., both using AES instead of DES). A key memory tip is to remember the acronym “EHA-D” for the four attributes that must match: Encryption, Hash, Authentication, and DH group—if any one differs, the SA fails.

300-410 IPsec Site-to-Site VPN Practice Question

This 300-410 practice question tests your understanding of ipsec site-to-site vpn. 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.

A network engineer runs the following command to troubleshoot an IPsec Site-to-Site VPN issue:

R1# debug crypto isakmp

*Mar  1 00:01:23.456: ISAKMP (0:0): received packet from 192.168.1.2 dport 500 sport 500 Global (N) NEW SA
*Mar  1 00:01:23.457: ISAKMP: Created a peer struct for 192.168.1.2, peer port 500
*Mar  1 00:01:23.457: ISAKMP: New peer created peer = 0x12345678 peer_handle = 0x80000001
*Mar  1 00:01:23.457: ISAKMP: Locking peer struct 0x12345678, refcount 1 for crypto_isakmp_process_block
*Mar  1 00:01:23.457: ISAKMP (0:0): SA request profile is (default)
*Mar  1 00:01:23.457: ISAKMP: local port 500, remote port 500
*Mar  1 00:01:23.458: ISAKMP (0:0): found peer pre-shared-key matching 192.168.1.2
*Mar  1 00:01:23.458: ISAKMP (0:0): constructed NAT-T vendor ID
*Mar  1 00:01:23.458: ISAKMP (0:0): sending packet to 192.168.1.2 my_port 500 peer_port 500 (I) MM_NO_STATE
*Mar  1 00:01:23.458: ISAKMP (0:0): received packet from 192.168.1.2 dport 500 sport 500 Global (I) MM_NO_STATE
*Mar  1 00:01:23.459: ISAKMP (0:0): processing SA payload. message ID = 0
*Mar  1 00:01:23.459: ISAKMP (0:0): Checking ISAKMP transform 1 against priority 1 policy
*Mar  1 00:01:23.459: ISAKMP:      encryption DES-CBC
*Mar  1 00:01:23.459: ISAKMP:      hash SHA
*Mar  1 00:01:23.459: ISAKMP:      default group 2
*Mar  1 00:01:23.459: ISAKMP:      auth pre-share
*Mar  1 00:01:23.459: ISAKMP (0:0): atts are not acceptable. Next transforms are not acceptable
*Mar  1 00:01:23.460: ISAKMP (0:0): no offers accepted!

What does this output indicate?

Question 1mediummultiple choice
Read the full VPN 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 ISAKMP transform set proposal is rejected due to a mismatch in encryption, hash, or DH group between peers.

The debug output shows that the router received an ISAKMP proposal from the peer (192.168.1.2) and checked it against its own configured policy. The line 'atts are not acceptable' followed by 'no offers accepted' indicates that the transform set attributes (encryption DES-CBC, hash SHA, DH group 2) did not match any of the router's ISAKMP policies. This is a classic proposal mismatch, preventing the ISAKMP SA from being established.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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 ISAKMP SA is established successfully using pre-shared key authentication.

    Why it's wrong here

    The debug shows 'no offers accepted', indicating failure, not success.

  • ✓

    The ISAKMP transform set proposal is rejected due to a mismatch in encryption, hash, or DH group between peers.

    Why this is correct

    The output clearly states 'atts are not acceptable' and 'no offers accepted', which means the proposed transform does not match the local policy.

    Related concept

    Read the scenario before looking for a memorised answer.

  • ✗

    The router is receiving the packet from an incorrect source IP address.

    Why it's wrong here

    The source IP is 192.168.1.2, which matches the expected peer; the issue is with transform mismatch, not source IP.

  • ✗

    The router is unable to find a pre-shared key for the peer.

    Why it's wrong here

    The debug shows 'found peer pre-shared-key matching 192.168.1.2', so the key is present.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the distinction between a pre-shared key mismatch (which would show 'no pre-shared key found') and a transform set mismatch (which shows 'atts are not acceptable'), leading candidates to incorrectly blame the PSK when the actual issue is the encryption/hash/DH group.

Trap categories for this question

  • Command / output trap

    The debug shows 'no offers accepted', indicating failure, not success.

Detailed technical explanation

How to think about this question

ISAKMP (IKEv1) Phase 1 uses transform sets containing encryption, hash, authentication, and Diffie-Hellman group attributes. The responder compares each received proposal against its configured policies in priority order; if no match is found, the SA negotiation fails. In real-world scenarios, common mismatches include using DES instead of AES, MD5 instead of SHA, or group 2 instead of group 5, often due to legacy configurations or copy-paste errors.

KKey Concepts to Remember

  • Read the scenario before looking for a memorised answer.
  • Find the constraint that changes the correct option.
  • Eliminate answers that are true in general but not in this case.

TExam Day Tips

  • Watch for words such as best, first, most likely and least administrative effort.
  • Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 300-410 question test?

IPsec Site-to-Site VPN — This question tests IPsec Site-to-Site VPN — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The ISAKMP transform set proposal is rejected due to a mismatch in encryption, hash, or DH group between peers. — The debug output shows that the router received an ISAKMP proposal from the peer (192.168.1.2) and checked it against its own configured policy. The line 'atts are not acceptable' followed by 'no offers accepted' indicates that the transform set attributes (encryption DES-CBC, hash SHA, DH group 2) did not match any of the router's ISAKMP policies. This is a classic proposal mismatch, preventing the ISAKMP SA from being established.

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

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jun 24, 2026

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