Exam CAS-004 topic 1 question 505 discussion

A. The IKE hashing algorithm uses different key lengths on each VPN device. In a site-to-site VPN setup, both ends must use compatible settings for the VPN to establish successfully. This includes parameters like the IKE hashing algorithm, encryption algorithm, and Diffie-Hellman group. If the hashing algorithms (or their key lengths) do not match on both sides, the IKE Phase 1 negotiation will fail, causing the error message described.

The error indicates an issue during Phase 1 of the IKE handshake, which is used for establishing secure key exchange in IPSec VPNs. If the Diffie-Hellman group is legacy (e.g., Group 1 or 2), it might no longer be supported by modern systems, causing the connection to fail. Updating to a stronger Diffie-Hellman group (e.g., Group 14 or 19) resolves this issue.

The error message indicates a failure during Phase 1 handshake, which is part of the IKE (Internet Key Exchange) process. IKE Phase 1 establishes a secure and authenticated channel for negotiating IPSec parameters. A mismatch in cryptographic settings, such as the hashing algorithm or key lengths, is a common cause of this type of failure.

The error message indicates a failure during the Phase 1 handshake of the VPN connection. Phase 1 establishes a secure channel for negotiating and authenticating the VPN connection. A mismatch in cryptographic parameters, such as the IKE (Internet Key Exchange) hashing algorithm or key lengths, is a common cause of such errors.

Ans. A. The error message "An error has occurred during Phase 1 handshake" suggests a problem during the initial negotiation of the VPN tunnel, often related to mismatches in configuration settings. The most likely reason for the connection failure is: A. The IKE hashing algorithm uses different key lengths on each VPN device. Inconsistent configurations between the two devices regarding the IKE settings, such as key lengths or hashing algorithms, can lead to failure in the Phase 1 handshake.

The Diffie-Hellman group on both sides matches but is a legacy group. Legacy DH groups (such as Group 1 or Group 2) are considered weak and may not be supported by modern security policies or configurations. If the DH group is outdated, it could cause the IKE Phase 1 handshake to fail, prompting errors related to key exchange issues.

The error message “An error has occurred during Phase 1 handshake. Deleting keys and retrying…” suggests that there is an issue with the initial negotiation or key exchange process. Legacy Diffie-Hellman groups are a common cause of such issues because modern VPN devices might reject or fail to negotiate with older, less secure groups.