set_iptables_dnat_fwding.sh

#!/bin/bash

set -E
trap 'echo Failed at $lineno COMMAND: $BASH_COMMAND && exit 1' ERR

SRV_IP="192.168.106.2"
SP_IP="192.168.105.2"

echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -F
iptables -t nat -F
iptables -X

# Forward UDP packets coming on port 25000 to SERVER-PROXY
iptables -t nat -A PREROUTING -p udp -m udp --dport 25000 -i eth0 -j DNAT --to-destination $SP_IP
iptables -A FORWARD -d $SP_IP -p udp --dport 25000 -j ACCEPT
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

# Forward UDP packets coming on port 60000-60099 to SERVER directly
iptables -t nat -A PREROUTING -p udp -m udp --dport 60000:60099 -i eth0 -j DNAT --to-destination $SRV_IP
iptables -A FORWARD -d $SRV_IP -p udp --dport 60000:60099 -j ACCEPT
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE