Blocking Packets with FIN Flag/No ACK Flag Set

A TCP header with the FIN flag set but not the ACK flag is anomalous TCP behavior, causing various responses from the recipient, depending on the OS. Blocking packets with the FIN flag and without the ACK flag helps prevent OS system probes.

You can use either J-Web or the CLI configuration editor to block packets with the FIN flag set but not the ACK flag.

This topic covers:

• J-Web Configuration
• CLI Configuration
• Related Topics

J-Web Configuration

1. Select CLI Tools>Point and Click CLI.
2. Next to Security, click Configure or Edit.
3. Next to Screen, click Configure.
4. Next to Ids option, click Add new entry.
5. In the Name box, type screen.
6. Next to Tcp, click Configure.
7. Next to Fin no ack, select the check box and click OK.
8. To save and commit the configuration, click Commit.

CLI Configuration

Related Topics

• Blocking Packets with SYN and FIN Flags Set
• Blocking Packets with SYN and FIN Flags Set