This protection must be enabled if you use your Linux server as a gateway to masquerade internal traffic to the Internet 
IP Masquerading.
            
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            [root@deep] /#echo 1 > /proc/sys/net/ipv4/ip_always_defrag
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            Add the above commands to the 
/etc/rc.d/rc.local script file and you'll not have to type it again the next time you reboot your system.
            
            
            Edit the 
/etc/sysctl.conf file and add the following line:
            
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            # Enable always defragging Protection
            net.ipv4.ip_always_defrag = 1
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            You must restart your network for the change to take effect. The command to manually restart the network is the following:
            
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            [root@deep] /# /etc/rc.d/init.d/network restart
            Setting network parameters	  [  OK  ]
            Bringing up interface lo	  [  OK  ]
            Bringing up interface eth0	  [  OK  ]
            Bringing up interface eth1	  [  OK  ]
             |