It indicates an attempt to exploit a Denial of Service vulnerability in Cisco IOS.
The vulnerability is due to an error when the application handles a malformed packet. A remote attack may be able to exploit this to cause a denial of service condition on the affected system.
Cisco IOS 11.2P
Cisco IOS 11.3T
Cisco IOS 12.0, 12.0T
Cisco IOS 12.1, 12.1T, 12.1E
Cisco IOS 12.2, 12.2T
Denial of Service: Remote attackers can crash vulnerable systems.
Upgrade to the latest version available from the website.