iptables -t nat -F
nic #
 iptables -F
nic #
 # NAT to NIC's address
nic #
 # NAT UDP 500,4500 to NICs address with sport
nic #
 iptables -t nat -A POSTROUTING -s 192.1.3.0/24 -p udp --sport 4500  -j SNAT --to-source 192.1.2.254:2500-2700
nic #
 iptables -t nat -A POSTROUTING -s 192.1.3.0/24 -p udp --sport 500  -j SNAT --to-source 192.1.2.254:3500-3700
nic #
 iptables -t nat -A POSTROUTING -s 192.1.3.0/24 -j SNAT --to-source 192.1.2.254
nic #
 echo done
done