> Source: [sk184257](https://support.checkpoint.com/results/sk/sk184257)

# sk184257 - Security Gateway on the 3900 appliance drops GRE packets that must go through NAT

| Property | Value |
|----------|-------|
| Solution ID | sk184257 |
| Date Created | 2025-11-20 |
| Last Modified | 2026-04-05 |
| Technical Level | General |
| Products | Security Gateway |
| Versions | R82.10 |
| OS | Gaia |
| Platform | 3900 |

## Symptoms

- * GRE packets that must go through NAT do not pass through the Security Gateway on the 3900 appliance.

* Kernel debug (`"fw ctl zdebug + drop"`) shows that SecureXL drops these GRE packets:

  `;do_packet_finish: SIMPKT_IN_DROP vsid=0, conn:<Source_IP_Address,0,Destination_IP_Address,0,47>;`  
  `
  ;sim_gre_parse_header: gre header flags: 0x10 is not right. Gre flag mask: 0xffff7fff ; `  
  `
  ;sim_gre_rcv: Error parsing GRE header, retval=3, gre_hdrlen=4;`

## Cause

Issue in the Check Point R82.10 version for 3900 appliances (released 01 June 2025 - see [sk183199](https://support.checkpoint.com/results/sk/sk183199))

## Solution

This problem was fixed. The fix is included starting from:

* [Check Point R82.10](https://support.checkpoint.com/results/sk/sk183506) (released 29 Dec 2025)

Check Point recommends to always upgrade to the [Recommended version](https://support.checkpoint.com/results/sk/sk95746).

If you choose not to upgrade, [contact Check Point Support](https://www.checkpoint.com/support-services/contact-support/) to get a Hotfix for your version.

A Support Engineer will make sure the Hotfix is compatible with your environment before providing it.  
For faster resolution and verification, collect these files:

1. [CPinfo](https://support.checkpoint.com/results/sk/sk92739) file from the Management Server involved in the case.
2. [CPinfo](https://support.checkpoint.com/results/sk/sk92739) file from the Security Gateway / each Cluster Member involved in the case.

**Hotfix installation instructions:**   
Refer to [sk168597 - How to install a Hotfix](https://support.checkpoint.com/results/sk/sk168597).

---

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