> Source: [sk33822](https://support.checkpoint.com/results/sk/sk33822)

# sk33822 - Site-to-Site VPN connection between Check Point VPN-1 and third-party gateways fails with (AUTHENTICATION-FAILED) error

| Property | Value |
|----------|-------|
| Solution ID | sk33822 |
| Date Created | 2007-11-06 |
| Last Modified | 2023-01-31 |
| Technical Level | Advanced |
| Products | Security Gateway |
| Versions | R81.20, R81.10 (EOS), R81 (EOS) |

## Symptoms

- * Scenario 1:
  * Site-to-Site VPN connection between Check Point VPN-1 and third-party gateways fails.
  * Error in IKE.elg file: `(AUTHENTICATION-FAILED)` is found in Main Mode packet 5 or 6.
* Scenario 2:
  * Site-to-Site VPN connection between Check Point VPN-1 and third-party gateways fails.
  * Error in IKE.elg file: `(AUTHENTICATION-FAILED)` is found in Main Mode packet 4.
  * The authentication method for the Site to Site is Pre-shared key (PSK).

## Cause

* In Scenario 1: The error message is received from the peer because it does not trust the ID sent to it.  

* In Scenario 2: The Pre-shared key (PSK) authentication failed due to non-identical Pre-shared key on all relevant peers or if no Pre-shared key was defined.

## Solution

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