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Difficulty: MediumVirtual Private Networks and Remote Access Security

A network administrator is documenting the authentication sequence for remote users connecting to an enterprise network using an IKEv2 IPsec Virtual Private Network (VPN) with EAP authentication. Place the following phases and steps of the IKEv2 negotiation process in the correct chronological order from first to last.

  1. 1The VPN client and gateway perform the IKE_SA_INIT exchange by negotiating encryption algorithms and exchanging Diffie-Hellman public keys to establish a secure control channel.
  2. 2The VPN client initiates the IKE_AUTH exchange inside the encrypted control channel by sending its identity and requesting EAP authentication.
  3. 3The VPN gateway acts as an authenticator, forwarding the remote user's authentication request to an internal RADIUS/AAA server.
  4. 4The VPN gateway completes the IKE_AUTH exchange, transmits configuration parameters (including an internal virtual IP address), and establishes the Child SA for user traffic.

Answer

The correct order of steps for establishing an IKEv2 remote access VPN session is: 1) Negotiate algorithms and exchange Diffie-Hellman keys during IKE_SA_INIT, 2) Send user identity and request EAP authentication during IKE_AUTH, 3) Proxy credential verification to the RADIUS server, and 4) Complete IKE_AUTH by assigning a virtual IP address and creating the Child SA.
Establishing an IKEv2 remote access VPN session requires a structured multi-phase process. First, the client and gateway initiate the IKE_SA_INIT exchange to negotiate cryptographic suites and exchange Diffie-Hellman public keys, forming a secure control tunnel. Second, the client initiates the IKE_AUTH exchange to submit its identity and select EAP authentication. Third, the VPN gateway proxies these EAP authentication messages to a backend RADIUS server for identity validation. Fourth, after the RADIUS server approves access, the gateway responds with the final IKE_AUTH message, assigning a local virtual IP address to the client and instantiating the Child SA used to protect actual data traffic.

Step-by-Step Solution

1
Identify the unauthenticated control phase (IKE_SA_INIT).
The client and VPN gateway establish shared secret keys using Diffie-Hellman and agree on encryption algorithms.
A secure, encrypted channel must be formed before transmitting sensitive authentication identity data.
2
Identify the start of the user authentication phase (IKE_AUTH).
The client requests authentication via Extensible Authentication Protocol (EAP) inside the secure control channel.
EAP negotiation occurs within the protection of the newly created IKE SA.
3
Identify backend credential verification.
The VPN gateway passes EAP messages to the RADIUS server to validate remote user credentials.
Enterprise VPNs rely on central AAA servers to verify identity and policy compliance.
4
Identify final session establishment and IP assignment.
The VPN gateway confirms authentication, provisions a virtual IP address via configuration payloads, and creates the Child SA.
The Child SA (IPsec SA) handles data transport after authorization is confirmed.

Key Concept

IKEv2 VPN Handshake and EAP Authentication Sequence
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Topics

Virtual Private Networks and Remote Access Security

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