Cisco Guard DDoS mitigation appliances from Cisco Systems contribute to the industry's most complete and powerful family of solutions for detecting and defeating today's highly complex and sophisticated distributed-denial-of-service (DDoS) attacks.

The Guard is a Distributed Denial of Service (DDoS) attack mitigation device that diverts suspect traffic from its normal network path to itself for cleaning. During the traffic cleaning process, the Guard identifies and drops the attack packets and forwards the legitimate packets to their targeted network destinations

For further information click this link.

http://www.cisco.com/en/US/docs/security/anomaly_detection_mitigation/appliances/guard/v6.1/configuration/guide/Intro.html