If you have existing access lists, you'll need to merge the new entries in an appropriate way, generally at the top of the list. We do not believe that this attack can be used against systems behind our dedicated firewall products, the PIX and Centri firewalls, unless general-purpose tunnels have been enabled through the firewalls. Properly designed anti-spoofing access lists at border routers can be used to prevent the attack from entering a private network from the Internet. Use the access lists to filter out packets whose IP source addresses are on your internal net, but which are arriving from interfaces connected to the outside Internet. Cisco has had multiple reports of this vulnerability.
Most exploitation seems to be using the original program, which sends one packet at a time.
Floods of invalid packets have not been reported. This issue has been widely discussed in a variety of Internet fora. Cisco first heard of this problem on the morning of Friday, November 21. Updates will be sent to some or all of these, as appropriate. Inc. This notice may be redistributed freely provided that redistributed copies are complete and unmodified, including all date and version information.