Mitigation features - Amazon WAF, Amazon Firewall Manager, and Amazon Shield Advanced
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Mitigation features

The main features of Amazon Shield DDoS mitigation are the following:

  • Packet validation – This ensures that every inspected packet conforms to an expected structure and is valid for its protocol. Supported protocol validations include IP, TCP (including header and options), UDP, ICMP, DNS, and NTP.

  • Access Control Lists (ACLs) and shapers – An ACL evaluates traffic against specific attributes and either drops matching traffic or maps it to a shaper. The shaper limits the packet rate for the matching traffic, dropping excess packets in order to contain the volume that reaches the destination. Amazon Shield detection and Shield Response Team (SRT) engineers can provide dedicated rate allocations to expected traffic and more restrictive rate allocations to traffic with attributes that match known DDoS attack vectors. The attributes that an ACL can match include the port, protocol, TCP flags, destination address, source country, and arbitrary patterns in the packet payload.

  • Suspicion scoring – This uses the knowledge that Shield has of expected traffic to apply a score to every packet. Packets that more closely adhere to patterns of known good traffic are assigned a lower suspicion score. Observation of known bad traffic attributes can increase the suspicion score for a packet. When it's necessary to rate limit packets, Shield drops packets with higher suspicion scores first. This helps Shield to mitigate both known and zero-day DDoS attacks while avoiding false positives.

  • TCP SYN proxy – This provides protection against TCP SYN floods by sending TCP SYN cookies to challenge new connections before allowing them to pass to the protected service. The TCP SYN proxy provided by Shield DDoS mitigation is stateless, which allows it to mitigate the largest known TCP SYN flood attacks without reaching state exhaustion. This is achieved by integrating with Amazon services to hand off connection state instead of maintaining a continuous proxy between the client and the protected service. TCP SYN proxy is currently available on Amazon CloudFront and Amazon Route 53.

  • Rate distribution – This continuously adjusts per-location shaper values based on the ingress pattern of traffic toward a protected resource. This prevents rate limiting of customer traffic that might not enter the Amazon network evenly.