> Source: [sk183639](https://support.checkpoint.com/results/sk/sk183639)

# sk183639 - Check Point Security Gateway drops the TCP [SYN-ACK] or [RST-ACK] packets with payload from F5 BIG-IP

| Property | Value |
|----------|-------|
| Solution ID | sk183639 |
| Date Created | 2025-07-09 |
| Last Modified | 2025-07-10 |
| Technical Level | Advanced |
| Products | Security Gateway, Scalable Platforms |
| Versions | R82, R81.20, R81.10 (EOS), R81 (EOS), R82, R81.20, R81.10 (EOS), R81 (EOS) |
| OS | Gaia |

## Symptoms

- * Connectivity issues between devices that communicate with F5 BIG-IP through a Check Point Security Gateway / Cluster.
* Kernel debug on the Security Gateway / Cluster Members (`fw ctl zdebug + drop | grep -E "<Source IP>|<Destination IP>"`) shows that the Security Gateway / Cluster Member drops the traffic with these reasons:

  1. `update_tcp_state: invalid response to SYN`
  2. `do_inbound: Possible TCP state violation for XXX -> dropping packet`

## Cause

By default, the Check Point Security Gateway drops the TCP \[RST\] packets that contain data in the payload. The Check Point TCP state engine considers TCP \[RST\] packets with data as a TCP state violation and drops them for security reasons. This behavior prevents potential security risks, such as attacks or information leak.

In the reported case, an F5 BIG-IP device was configured to include a diagnostic message in the TCP \[RST\] packet payload.

## Solution

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