echo 1 > cat /proc/sys/net/ipv4/ip_forward

# 100.100.100.100:1337 -> 200.200.200.200:1337
# replace "-A" with "-D" to delete rule
iptables -t nat -A PREROUTING -p tcp --dport 1337 -j DNAT --to-destination 100.100.100.100:1337
iptables -t nat -A POSTROUTING -p tcp -d 100.100.100.100 --dport 1337 -j SNAT --to-source 200.200.200.200