I use linux kernel 2.6. I have enabled SYN cookies already. But that does not seem to solve the problem. Overall request latency is very high with these many half open connections. Thanks and Regards Puneet ----------------------------------------
Subject: Re: lots of connections in SYN_RECV state From: dave.jing.tian@gmail.com Date: Fri, 7 Nov 2014 23:49:35 +0800 CC: puneet.agr@outlook.com; kernelnewbies@kernelnewbies.org To: me@sillymon.ch
Latest kernel provides a TCP SYN Cookie feature to defense from SYN flooding.
-daveti
On Nov 6, 2014, at 11:58 PM, Silvan Jegen <me@sillymon.ch> wrote:
2014-11-06 16:15,Puneet Agarwal:
Is there a way to check the reason, why they do not answer to the SYN-ACK's?
I don't think so. After all, they just don't answer and they won't tell you why (AFAIK there is no way to ask them why either)...
You could try to check for patterns in the incoming IP addresses to see from how many different places these connections are being made. I think that way it should be possible to figure out from which geographic location these problematic connections are coming from as well. What you would do with these findings I am not sure though.
If these connection negatively impact the performance of your servers you should definitely look into to countermeasures mentioned in the RFC here.
http://tools.ietf.org/html/rfc4987
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