300-410 VPN Technologies Practice Question
A network administrator is setting up a site-to-site VPN between two Cisco IOS routers and wants to use IKEv2 with certificate-based authentication. The administrator has already installed the identity certificate and the CA certificate on both routers. Which additional configuration is required on each router so that IKEv2 can validate the peer's certificate during the IKE_AUTH exchange?
⚠ Common exam trap
The trap here is believing that installing certificates is sufficient, when IKEv2 also needs an explicit trustpoint reference in the profile to know which CA chain to use.
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
✓
Reference the PKI trustpoint in the IKEv2 profile using the pki trustpoint command so the router knows which CA to use for validation.
IKEv2 certificate authentication requires the router to select a trustpoint that identifies its own certificate and the CA chain used to validate the peer. The pki trustpoint command under the IKEv2 profile provides that binding. With the trustpoint referenced, the router can present its identity certificate and verify the peer's certificate during IKE_AUTH, completing authentication even though the certificates were already installed.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure a pre-shared key on both routers as a fallback in case certificate validation fails.
Why it's wrong here
Adding a pre-shared key does not help certificate validation and can create an authentication mismatch. If the IKEv2 profile is set for certificate authentication, a pre-shared key fallback is not used for that profile and may cause confusion during troubleshooting. The requirement is to have the router find the CA chain for validation, which is done through the trustpoint reference, not through a PSK.
- ✗
Configure the IKEv2 profile with the authentication local rsa-sig command only, without referencing a trustpoint.
Why it's wrong here
Specifying rsa-sig authentication indicates the method but does not tell the router which certificate or CA chain to use. Without a trustpoint reference, the router cannot determine which installed certificate to present or which CA to trust for the peer. The trustpoint binding is the required element, so this option is incomplete and the negotiation would still fail.
- ✓
Reference the PKI trustpoint in the IKEv2 profile using the pki trustpoint command so the router knows which CA to use for validation.
Why this is correct
For certificate authentication in IKEv2, the router must know which trustpoint to use for its own certificate and for validating the peer certificate chain. Referencing the trustpoint in the IKEv2 profile with the pki trustpoint command supplies that binding. Without it, the router cannot select the correct CA chain or send the proper certificate during IKE_AUTH, so the negotiation fails even though certificates are installed.
- ✗
Enable the crypto pki server on both routers so each can issue certificates to the other.
Why it's wrong here
A PKI server issues certificates, but the routers already have identity and CA certificates installed from an existing CA. Running a local PKI server on each router would create separate trust domains and is unnecessary. The missing piece is telling IKEv2 which trustpoint to use for validation, not adding a certificate authority function to the endpoints.
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.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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