This 300-410 practice question tests your understanding of ipsec site-to-site vpn. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Which authentication method is used by default in IKEv1 main mode for IPsec site-to-site VPN on Cisco IOS?
RSA signatures
Why wrong: RSA signatures require digital certificates and are not the default.
Pre-shared keys
PSK is the default authentication method for IKEv1.
Elliptic Curve Digital Signature Algorithm (ECDSA)
Why wrong: ECDSA is not a default; it is used in advanced configurations.
No default; authentication must be explicitly configured
Why wrong: PSK is the default if no method is specified.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Pre-shared keys
In Cisco IOS, IKEv1 main mode for IPsec site-to-site VPN defaults to pre-shared keys (PSK) as the authentication method. This is because PSK is the simplest to configure and does not require a public key infrastructure (PKI), making it the default choice when no other authentication method is explicitly specified. The configuration commands like 'crypto isakmp key' directly implement PSK authentication.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
RSA signatures
Why it's wrong here
RSA signatures require digital certificates and are not the default.
Pre-shared keys
Why this is correct
PSK is the default authentication method for IKEv1.
Related concept
Read the scenario before looking for a memorised answer.
Elliptic Curve Digital Signature Algorithm (ECDSA)
Why it's wrong here
ECDSA is not a default; it is used in advanced configurations.
No default; authentication must be explicitly configured
Why it's wrong here
PSK is the default if no method is specified.
Common exam traps
Cisco often tests the misconception that IKEv1 has no default authentication method, leading candidates to choose 'No default; authentication must be explicitly configured' when in fact pre-shared keys are the default.
Detailed technical explanation
IKEv1 main mode uses three pairs of messages, with the third pair carrying authentication data. When using pre-shared keys, both peers derive a shared secret from the configured key and use it to authenticate each other via a hash (e.g., HMAC-SHA). In contrast, RSA signatures involve signing the Diffie-Hellman exchange with a private key, which requires certificate management and is more secure but operationally heavier. Cisco IOS defaults to PSK to simplify initial setup, but this can be a security risk in large deployments if keys are not rotated.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
IPsec Site-to-Site VPN — This question tests IPsec Site-to-Site VPN — Read the scenario before looking for a memorised answer..
The correct answer is: Pre-shared keys — In Cisco IOS, IKEv1 main mode for IPsec site-to-site VPN defaults to pre-shared keys (PSK) as the authentication method. This is because PSK is the simplest to configure and does not require a public key infrastructure (PKI), making it the default choice when no other authentication method is explicitly specified. The configuration commands like 'crypto isakmp key' directly implement PSK authentication.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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