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Hierarchy Level


Prevent port scan attacks. A port scan attack occurs when an attacker sends packets with different port numbers to scan available services. The attack succeeds if a port responds. To prevent this attack, the device internally logs the number of different ports scanned from a single remote source. For example, if a remote host scans 10 ports in 0.005 seconds (equivalent to 5000 microseconds, the default threshold setting), the device flags this behavior as a port scan attack, and rejects further packets from the remote source.


threshold number —Number of microseconds during which the device accepts packets from the same remote source with up to 10 different port numbers. If the number of ports during the threshold period reaches 10 or more, the device rejects additional packets from the source.

  • Range: 1000 through 1,000,000 microseconds

  • Default: 5000 microseconds

Required Privilege Level

security—To view this statement in the configuration.

security-control—To add this statement to the configuration.

Release Information

Statement introduced in Junos OS Release 8.5.