> Source: [sk173191](https://support.checkpoint.com/results/sk/sk173191)

# sk173191 - Packet data stripped by "TCP Invalid Checksum" IPS protection

| Property | Value |
|----------|-------|
| Solution ID | sk173191 |
| Date Created | 2021-04-23 |
| Last Modified | 2024-08-19 |
| Technical Level | Advanced |
| Products | Security Gateway |
| Versions | R81.20, R81.10 (EOS), R81 (EOS) |
| OS | Gaia |

## Symptoms

- * Traffic is dropped by the core IPS protection "TCP Invalid Checksum".

* The Security Gateway strips the payload data from a retransmitted ACK packet.

## Cause

The ***TCP Invalid Checksum*** protection drops packets that arrive in the window in which ACK data is retained on the firewall. If re-transmission of a packet arrives late and outside of this window, the data is stripped from the packet. The Security Gateway then sends the packet as a bare ACK to preserve the stream.

## Solution

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