The answer is a Phase 2 authentication algorithm mismatch, specifically that Phase 2 uses SHA-1 while Phase 1 uses SHA-256. This is correct because in IPsec VPN, Phase 1 establishes the ISAKMP SA with a set of encryption and authentication algorithms, but Phase 2 negotiates the IPsec SA for actual data traffic; critically, the authentication algorithm must be consistent across both phases for the tunnel to build. On the Fortinet NSE 7 Advanced Security NSE7 exam, this scenario tests your understanding of IKE proposal compatibility—a common trap is assuming Phase 1 and Phase 2 algorithms are independent, when in fact the authentication hash must match exactly. A reliable memory tip: think of Phase 1 as the handshake and Phase 2 as the data lock—if the handshake uses SHA-256, the lock cannot use SHA-1, or the keys won’t turn.
NSE7 Advanced VPN and Zero Trust Practice Question
This NSE7 practice question tests your understanding of advanced vpn and zero trust. 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.
Exhibit
Refer to the exhibit.
config vpn ipsec phase1-interface
edit "Branch_Tunnel"
set interface "wan1"
set peertype any
set net-device disable
set proposal aes256-sha256
set dhgrp 14
set remote-gw 203.0.113.10
set psksecret ENC XXXX
next
end
config vpn ipsec phase2-interface
edit "Branch_Tunnel_p2"
set phase1name "Branch_Tunnel"
set proposal aes256-sha1
set src-addr-type name
set dst-addr-type name
set src-name "local_net"
set dst-name "remote_net"
next
end
Refer to the exhibit. A FortiGate administrator has configured an IPsec VPN tunnel to a branch office. The tunnel fails to establish. What is the most likely cause?
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.
Refer to the exhibit.
config vpn ipsec phase1-interface
edit "Branch_Tunnel"
set interface "wan1"
set peertype any
set net-device disable
set proposal aes256-sha256
set dhgrp 14
set remote-gw 203.0.113.10
set psksecret ENC XXXX
next
end
config vpn ipsec phase2-interface
edit "Branch_Tunnel_p2"
set phase1name "Branch_Tunnel"
set proposal aes256-sha1
set src-addr-type name
set dst-addr-type name
set src-name "local_net"
set dst-name "remote_net"
next
end
A
Phase 2 proposal (aes256-sha1) is not compatible with Phase 1 proposal (aes256-sha256)
Phase 2 encryption must be a subset of Phase 1; SHA1 vs SHA256 mismatch causes failure.
B
The pre-shared key is encrypted in the configuration
Why wrong: PSK encryption is normal and doesn't affect connectivity.
C
The 'net-device disable' setting prevents tunnel creation
Why wrong: net-device disable is optional and doesn't prevent tunnel establishment.
D
The phase2 interface name does not match the phase1 name
Why wrong: phase1name references the correct Phase 1.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Phase 2 proposal (aes256-sha1) is not compatible with Phase 1 proposal (aes256-sha256)
The tunnel fails because the Phase 2 proposal (aes256-sha1) is not compatible with the Phase 1 proposal (aes256-sha256). In IPsecVPN, Phase 1 establishes the ISAKMP SA using a set of encryption and authentication algorithms, while Phase 2 negotiates the IPsec SA for data traffic. The authentication algorithm must match between Phase 1 and Phase 2; here, Phase 1 uses SHA-256 but Phase 2 uses SHA-1, causing a mismatch that prevents the tunnel from establishing.
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.
✓
Phase 2 proposal (aes256-sha1) is not compatible with Phase 1 proposal (aes256-sha256)
Why this is correct
Phase 2 encryption must be a subset of Phase 1; SHA1 vs SHA256 mismatch causes failure.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The pre-shared key is encrypted in the configuration
Why it's wrong here
PSK encryption is normal and doesn't affect connectivity.
✗
The 'net-device disable' setting prevents tunnel creation
Why it's wrong here
net-device disable is optional and doesn't prevent tunnel establishment.
✗
The phase2 interface name does not match the phase1 name
Why it's wrong here
phase1name references the correct Phase 1.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume Phase 1 and Phase 2 proposals are independent, but FortiGate requires the authentication algorithm to match between phases, and the exam tests this subtle interoperability constraint.
Detailed technical explanation
How to think about this question
In IPsec, Phase 1 (IKE) negotiates the ISAKMP SA with a proposal set that includes encryption, authentication, DH group, and lifetime. Phase 2 (IPsec) negotiates the IPsec SA with its own proposal set, but the authentication algorithm must be consistent with the Phase 1 SA's authentication method (e.g., if Phase 1 uses SHA-256, Phase 2 cannot use SHA-1 because the integrity check fails). This is a common misconfiguration in multi-vendor environments where default proposals differ; FortiGate logs will show 'proposal mismatch' in the IKE debug output.
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.
Advanced VPN and Zero Trust — This question tests Advanced VPN and Zero Trust — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Phase 2 proposal (aes256-sha1) is not compatible with Phase 1 proposal (aes256-sha256) — The tunnel fails because the Phase 2 proposal (aes256-sha1) is not compatible with the Phase 1 proposal (aes256-sha256). In IPsec VPN, Phase 1 establishes the ISAKMP SA using a set of encryption and authentication algorithms, while Phase 2 negotiates the IPsec SA for data traffic. The authentication algorithm must match between Phase 1 and Phase 2; here, Phase 1 uses SHA-256 but Phase 2 uses SHA-1, causing a mismatch that prevents the tunnel from establishing.
What should I do if I get this NSE7 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
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