Proxy SYN Cookie Activation for Half-Open TCP Floods
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Solution Overview
Problem
SYN flood attacks deplete processing resources in proxy devices like firewall devices, leading to denial of service, as existing SYN cookie protection mechanisms consume resources and are ineffective when implemented in proxy devices.
Innovation Solution
A dynamic SYN cookie protection mechanism in a firewall device selectively activates SYN cookie protection based on the count of half-open TCP flows exceeding a threshold, using a SYN cookie activation rule to manage resource allocation and reduce computational overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SYN cookie protection is implemented in a proxy device, then protection against SYN flood attacks is improved, but processing resources are depleted due to sequence number translations and checksum re-computations
Solution Approach 1:
The patent implements dynamic SYN cookie protection that can be selectively activated or deactivated based on network conditions. The proxy device monitors for SYN flood attack patterns and only enables the computationally intensive SYN cookie mechanism when attacks are detected, rather than maintaining it continuously. This dynamic approach allows the system to have protection capability available when needed while avoiding unnecessary resource consumption during normal operation.
Solution Approach 2:
The patent changes the operational parameters of the proxy device by switching between different protection modes. When SYN flood attacks are detected, the system changes from a standard TCP processing mode to a SYN cookie protection mode, altering how sequence numbers are handled and when checksums are computed. This parameter change allows the system to adapt its resource usage based on threat levels.
2Reliability
If SYN cookie protection is continuously active, then protection against SYN flood attacks is maintained, but resource depletion occurs over time leading to denial of service
Solution Approach 1:
The patent implements periodic monitoring of network traffic patterns to detect SYN flood attacks. Instead of having SYN cookie protection continuously active, the system periodically checks for attack conditions and activates protection only during threat periods. This periodic action maintains service availability by avoiding continuous resource consumption while ensuring protection is available when needed.
Solution Approach 2:
The system uses feedback from network traffic monitoring to control the activation of SYN cookie protection. The proxy device continuously monitors incoming traffic patterns and uses this feedback to determine when to activate or deactivate protection mechanisms. This feedback-based control ensures that protection is maintained during attacks while preserving service availability during normal operation by avoiding unnecessary resource depletion.
Data Source
AI summary
In some examples, a proxy device tracks a count of how many half-open Transmission Control Protocol (TCP) flows are present in the proxy device. Based on the count breaching a threshold, the proxy device triggers activation, at the proxy device, of SYN cookie protection from an inactive state, where the SYN cookie protection includes generating an initial sequence number for a SYN-ACK packet based on applying a function on TCP state information associated with a received SYN packet from a client device. The SYN packet is to initiate a TCP flow between the client device and a server device, and the SYN-ACK packet is sent by the proxy device to the client device in response to the SYN packet.