Configuration of Restricted NAT

Here I provides two example to setup the Address-Restriced NAT in ubuntu 12.04 by using iptables and ipset.

1. for a fixed client ip address

 1    iptables -t nat -A POSTROUTING -p UDP -o $EXTIF -j SNAT --to-source 
 2    $EXTIP
 3    iptables -t nat -A PREROUTING -i $EXTIF -j DNAT --to-destination 
 4    $CLIENTIP
 5    iptables -A FORWARD -i $EXTIF -j DROP
 6  
 7    ipset -N RES_CONDITION ipporthash -exist
 8    ipset flush RES_CONDITION
 9    iptables -A FORWARD -o $EXTIF -j SET --add-set RES_CONDITION dst,
10    src
11    iptables -I FORWARD 1 -i $EXTIF -m set --match-set RES_CONDITION 
12    src,dst -j ACCEPT

Reference:

• iptables usage

• http://www.netfilter.org/documentation/HOWTO/netfilter-extensions-HOWTO-3.html

• ipset usage

• http://man.cx/ipset(8)

• http://ipset.netfilter.org/ipset.man.html