Here is a clear example of what I am up against

tcp        0      0 192.168.1.3:80          51.189.12.20:44005 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:3241 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:45024 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:45581 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:35868 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:13274 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:61994 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:12884 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:27740 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:42770 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:42194 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:19983 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:65348 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:15570 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:31954 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:20130 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:10930 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:5062 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:63390 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:2011 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:11260 
SYN_RECV
tcp        0      0 192.168.1.1:80          51.189.12.20:38595 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:62897 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:30273 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:43825 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:7057 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:41971 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:41182 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:10025 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:16376 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:37065 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:57915 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:64800 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:58396 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:854 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:7538 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:46706 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:63466 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:46577 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:26128 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:7494 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:23729 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:60079 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:9427 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:13672 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:22563 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:26838 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:50520 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:41887 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:53727 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:59903 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:11863 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:48149 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:58911 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:29155 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:52098 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:60030 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:1246 
SYN_RECV
tcp        0      0 192.168.1.3:80          151.189.12.20:35726 
SYN_RECV
tcp        0      0 192.168.1.1:80          151.189.12.20:25560 
SYN_RECV

I am going to block this guy and figure it out later.

William L. Thomson Jr. wrote:

> I seem to have allot of entries in my dmesg log like the following
> 
> possible SYN flooding on port 80. Sending cookies.
> 
> Now using netstat I saw some connections similar to
> 
> www.obsidian-studios.com:www  66-182-46-206.atgi:2781 SYN_RECV
> 
>  From time to time a particular IP address will have multiple lines like 
> the one above with multiple connections to each IP site on my server.
> 
> I have begun denying service to certain IP's that look like they are 
> abusing the server. So far I have denied all access from 6 IP addresses.
> 
> Although I am not to sure if that is what I should have done or not.
> 
> The kernel seems to have tcp_syncookies enabled, which I think is 
> correct, I can turn it off if it will help. But it is one by default, I 
> never turned it on.
> 
> Anyway I just want to make sure that I am addressing this situation 
> properly and not blocking people out of the server who are not trying to 
> abuse it.
> 
> Is this something I need to be concerned with, and what should I do 
> about it? It seems that after a period of time even IP that have 
> multiple SYN_RECV connections end up disappearing. I am starting to 
> second guess my decision to block out those IP's.
> 
> Any comments advice. Either is greatly appreciated.
> 


-- 
Sincerely,
William L. Thomson Jr.
Support Group
Obsidian-Studios Inc.
439 Amber Way
Petaluma, Ca. 94952
Phone   707.766.9509
Fax 
707.766.8989
http://www.obsidian-studios.com

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