> Source: [sk35633](https://support.checkpoint.com/results/sk/sk35633)

# sk35633 - What is FIN URG ACK generated by Security gateway

| Property | Value |
|----------|-------|
| Solution ID | sk35633 |
| Date Created | 2008-07-28 |
| Last Modified | 2023-03-03 |
| Technical Level | General |
| Products | Security Gateway |
| Versions | R82.10, R82, R81.20 |

## Solution

When installing a Security Policy with the "Rematch connections" option selected (Connection Persistence section in the gateway properties), the firewall will attempt to confirm the validity of all new connections with the following process:   

1. The firewall removes all data from the packet and adds the URG flag.   

2. The firewall returns the packet to the source of the connection, expecting to receive an Acknowledgment (ACK) from the source machine for that packet.   

3. If an Acknowledgment (ACK) arrives from the source machine, the firewall will allow this connection. However, if no Acknowledgment (ACK) arrives from the source machine, the firewall considers the connection "dead" and closes this connection.

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