2015-11-30 18:05:41 UTC
Using boost::asio for basic network connectivity and I'm working on hardening the system to mitigate SYN flood DOS attacks. I've been looking at using SYN cookies which have been a very common approach for the last 20 years - they were first proposed and implemented in 1996. I'm sure most people here will know how they work but essentially they avoid committing resources for an incoming TCP connection until they get confirmation that the connection request is "real". (Briefly, they encode enough information in the SYN-ACK sequence number to reconstruct the connection information and don't fully process the connection until they get the ACK and use the sequence number to finish processing the connection. This allows a server to avoid committing any resources unless the incoming client is willing to send the SYN ACK which it often isn't in a SYN flood DOS attack.)
My question is: How does boost::asio figure in here? I'm assuming that enabling the use of SYN cookies is transparent to asio but if asio processes the connection on the SYN (allocating some resources) and doesn't wait til the ACK then it defeats the SYN flood mitigation effect of the SYN cookies. Anybody have enough knowledge of the low-level plumbing to know what the interaction is?
Alternately I'd like to know if there's any built-in or standard boost facility for mitigating SYN flood attacks; I could try to handle it at a higher level but it's such a common problem and best handled at the connection establishment layer that I figured that there must be a common approach - is there?
Thanks in advance for any consideration ... N
Senior Firmware Developer, Security Specialist
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