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Blocking Packets with No Flags Set

A TCP segment with no control flags set is an anomalous event, causing various responses from the recipient, depending on the OS. Blocking packets with no flags set helps prevent OS system probes. When you enable the device to detect TCP segment headers with no flags set, the device drops all TCP packets with a missing or malformed flags field.

Before You Begin
For background information, read Understanding Operating System Probes.

You can use either J-Web or the CLI configuration editor to block packets with no flags set.

This topic covers:

J-Web Configuration

To configure screens:

Select CLI Tools>Point and Click CLI.
Next to Security, click Configure or Edit.
Next to Screen, click Configure.
Next to Ids option, click Add new entry.
In the Name box, type tcp-no-flag.
Next to Tcp, click Configure.
Next to tcp no flag, select the check box and click OK.
To save and commit the configuration, click Commit.

To configure zones:

Select CLI Tools>Point and Click CLI.
Next to Security, click Configure or Edit.
Next to Zones, click Configure.
Next to Security zone, click Add new entry.
In the Name box, type zone.
In the Screen box, type tcp-no-flag and click OK.
To save and commit the configuration, click Commit.

CLI Configuration


            
               user@host# set security screen ids-option
                     tcp-no-flag tcp tcp-no-flag
               user@host# set security zones security-zone
                     zone screen tcp-no-flag

Blocking Packets with No Flags Set

J-Web Configuration

CLI Configuration

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