[Box-Admins] About the server downtime today

Levente Uzonyi leves at elte.hu
Fri Oct 21 15:13:02 UTC 2011


Hi,

the webserver stopped responding today, while ping was working fine. I 
contacted Bert on IRC who gave me access to the box. As he suggested I 
tried restarting apache, which temporarily solved the problem, but in 
10-20 minutes the server went down again. At this point there were several 
connections to port 80 in SYN_RECV state, which is a sign of a possible 
SYN flood attack. I did a few more apache restarts and I installed tcpdump 
in order to find out the cause, but after checking quite a few 
(non-suspicious) connections, I gave up. I enabled tcp_syncookies on the 
server which solved the problem without further apache restarts.

Cheers,
Levente


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