SYN Cookie is a stateless SYN proxy mechanism you can use in conjunction with traditional SYN flood defenses to protect the NetScreen device against a SYN flood attack. Like traditional SYN proxy, SYN Cookie is activated when the syn-flood attack-threshold is exceeded, therefore you must set an attack threshold before enabling SYN Cookie. To Enable SYN-Cookie
To enable the SYN Cookie feature globally on the NetScreen device:
Set a SYN flood attack threshold (see Screen Options).
Check the TCP SYN proxy SYN cookie checkbox.
Click Apply to save your settings.