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I am trying to enable syn cookies in a server, but I can't.

root@server [~]# echo '1' > /proc/sys/net/ipv4/tcp_syncookies
root@server [~]# cat /proc/sys/net/ipv4/tcp_syncookies
0
root@server [~]# 

What is wrong, and how could I enable syn cookies?

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Are there any log messages (dmesg, kern, syslog)? sysctl net.inet.tcp.syncookies does say the same thing? Is /proc really the /proc you expect (this stands for the basic questions like mountpoints set up properly and not just writing to some directory structure that looks like /proc) –  Server Horror Jun 12 '11 at 19:11
    
@ServerHorror /proc is the /proc I expect, sysctl net.ipv4.tcp_syncookies outputs net.ipv4.tcp_syncookies = 0 and dmesg outputs nothing. –  Artur Gaspar Jun 12 '11 at 19:40
    
Is this a physical server or a virtual server? –  Janne Pikkarainen Jun 13 '11 at 6:50
    
@Janne Pikkarainen It is a virtual server. –  Artur Gaspar Jun 13 '11 at 22:53
    
What is the output of lsattr /proc/sys/net/ipv4/tcp_syncookies –  mossy Dec 7 '11 at 21:09
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