Guess what: it is possible!. Judy Novak posted an excellent article demonstrating it. Read it at http://www.packetstan.com/2010/07/potential-evasion-where-ips-fails-to.html

-- Manuel Humberto Santander Peláez | http://twitter.com/manuelsantander | http://manuel.santander.name | msantand at isc dot sans dot org