Securing and Optimizing Linux: RedHat Edition -A Hands on Guide
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6.7. The ip_local_port_range parameters

The /proc/sys/net/ipv4/ip_local_port_range defines the local port range that is used by TCP and UDP traffic to choose the local port. You will see in the parameters of this file two numbers: The first number is the first local port allowed for TCP and UDP traffic on the server, the second is the last local port number. For high-usage systems you may change its default parameters to 32768-61000 -first-last.

The default setup for the ip_local_port_range parameters under Red Hat Linux is: "1024 4999"

Version 6.1 only

To change the values of ip_local_port_range, type the following command on your terminal: 

            [root@deep] /# echo "32768 61000" >/proc/sys/net/ipv4/ip_local_port_range
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.

Version 6.2 only

Edit the /etc/sysctl.conf file and add the following line: 

            # Allowed local port range
            net.ipv4.ip_local_port_range = 32768 61000
You must restart your network for the change to take effect. The command to manually restart the network is the following: 

            [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 ]  

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