How to configure firewall for the better performance of Openvpn

This article explains the detailed steps to configure the firewall for the better performance of openvpn server.

If your server is a Dedicated server or XEN VPS server then:

Code:
#!/bin/sh
#
# iptables example configuration script
#
# Flush all current rules from iptables
#
iptables -F
iptables -t nat -F
iptables -t mangle -F

#
# Allow SSH connections on tcp port 22 (or whatever port you want to use)
#
iptables -A INPUT -p tcp --dport 22 -j ACCEPT

#
# Set default policies for INPUT, FORWARD and OUTPUT chains
#
iptables -P INPUT DROP #using DROP for INPUT is not always recommended. Change to ACCEPT if you prefer.
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT

#
# Set access for localhost
#
iptables -A INPUT -i lo -j ACCEPT

#
# Accept packets belonging to established and related connections
#
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

#
#Accept connections on 1194 for vpn access from clients
#Take note that the rule says "UDP", and ensure that your OpenVPN server.conf says UDP too
#
iptables -A INPUT -p udp --dport 1194 -j ACCEPT

#
#Apply forwarding for OpenVPN Tunneling
#
iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -s 10.8.0.0/24 -j ACCEPT #10.8.0.0 ? Check your OpenVPN server.conf to be sure
iptables -A FORWARD -j REJECT
iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE

#
#Enable forwarding
#
echo 1 > /proc/sys/net/ipv4/ip_forward
#
# Some generally optional rules. Enable and disable these as per your requirements
#

# Accept traffic with the ACK flag set
iptables -A INPUT -p tcp -m tcp --tcp-flags ACK ACK -j ACCEPT
# Accept responses to DNS queries
iptables -A INPUT -p udp -m udp --dport 1024:65535 --sport 53 -j ACCEPT
# Accept responses to our pings
iptables -A INPUT -p icmp -m icmp --icmp-type echo-reply -j ACCEPT
# Accept notifications of unreachable hosts
iptables -A INPUT -p icmp -m icmp --icmp-type destination-unreachable -j ACCEPT
# Accept notifications to reduce sending speed
iptables -A INPUT -p icmp -m icmp --icmp-type source-quench -j ACCEPT
# Accept notifications of lost packets
iptables -A INPUT -p icmp -m icmp --icmp-type time-exceeded -j ACCEPT
# Accept notifications of protocol problems
iptables -A INPUT -p icmp -m icmp --icmp-type parameter-problem -j ACCEPT
# Respond to pings
iptables -A INPUT -p icmp -m icmp --icmp-type echo-request -j ACCEPT
# Accept traceroutes
iptables -A INPUT -p udp -m udp --dport 33434:33523 -j ACCEPT

#
# List rules
#
iptables -L -v
If your server is an openVZ VPS then:

Code:
#!/bin/sh
#
# iptables example configuration script
#
# Flush all current rules from iptables
#
iptables -F
iptables -t nat -F
iptables -t mangle -F

#
# Allow SSH connections on tcp port 22 (or whatever port you want to use)
#
iptables -A INPUT -p tcp --dport 22 -j ACCEPT

#
# Set default policies for INPUT, FORWARD and OUTPUT chains
#
iptables -P INPUT DROP #using DROP for INPUT is not always recommended. Change to ACCEPT if you prefer.
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT

#
# Set access for localhost
#
iptables -A INPUT -i lo -j ACCEPT

#
# Accept packets belonging to established and related connections
#
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

#
#Accept connections on 1194 for vpn access from clients
#Take note that the rule says "UDP", and ensure that your OpenVPN server.conf says UDP too
#
iptables -A INPUT -p udp --dport 1194 -j ACCEPT

#
#Apply forwarding for OpenVPN Tunneling
#
iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -s 10.8.0.0/24 -j ACCEPT #10.8.0.0 ? Check your OpenVPN server.conf to be sure
iptables -A FORWARD -j REJECT
iptables -t nat -A POSTROUTING -o venet0 -j SNAT --to-source 100.200.255.256 #Use your OpenVPN server's real external IP here

#
#Enable forwarding
#
echo 1 > /proc/sys/net/ipv4/ip_forward
#
# Some generally optional rules. Enable and disable these as per your requirements
#

# Accept traffic with the ACK flag set
iptables -A INPUT -p tcp -m tcp --tcp-flags ACK ACK -j ACCEPT
# Accept responses to DNS queries
iptables -A INPUT -p udp -m udp --dport 1024:65535 --sport 53 -j ACCEPT
# Accept responses to our pings
iptables -A INPUT -p icmp -m icmp --icmp-type echo-reply -j ACCEPT
# Accept notifications of unreachable hosts
iptables -A INPUT -p icmp -m icmp --icmp-type destination-unreachable -j ACCEPT
# Accept notifications to reduce sending speed
iptables -A INPUT -p icmp -m icmp --icmp-type source-quench -j ACCEPT
# Accept notifications of lost packets
iptables -A INPUT -p icmp -m icmp --icmp-type time-exceeded -j ACCEPT
# Accept notifications of protocol problems
iptables -A INPUT -p icmp -m icmp --icmp-type parameter-problem -j ACCEPT
# Respond to pings
iptables -A INPUT -p icmp -m icmp --icmp-type echo-request -j ACCEPT
# Accept traceroutes
iptables -A INPUT -p udp -m udp --dport 33434:33523 -j ACCEPT

#
# List rules
#
iptables -L -v
Exicution:

Save the scripts as firewall_setup_script.sh and chmod to 755. Execute the script at the Linux command line.

Testing:

From your client, connect to the OpenVPN server. Visit http://www.whatismyip.com, and take note whether your IP is shown as your ISP IP or your VPN server IP.

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