> Source: [sk181381](https://support.checkpoint.com/results/sk/sk181381)

# sk181381 - Site-to-Site tunnel fails intermittently between a Security Gateway and another device defined as a DAIP gateway behind Hide NAT

| Property | Value |
|----------|-------|
| Solution ID | sk181381 |
| Date Created | 2023-08-14 |
| Last Modified | 2026-01-27 |
| Technical Level | Advanced |
| Products | Security Gateway |
| Versions | R81.20, R81.10 (EOS) |
| OS | Gaia |

## Symptoms

- * The SMB (or other DAIP) gateways are DAIP behind a NAT device.

* Traffic from the center shows tunnel initiation on port 500 and then switches to 4500 (NAT-T) instead of initiating with port 4500.

* IKE error on the SMB side shows "*INVALID-CERTIFICATE*."

* The issue persists even after deleting the tunnel completely on the center side.

## Cause

A new mechanism was added to allow the gateway to properly detect DAIP device behind Hide-NAT.

## Solution

This solution requires authentication. Please log in to view the full solution.

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