А вот сам скрипт ...
#!/bin/sh
REAL_IP="192.168.0.1"
REAL_IFACE="eth0"
REAL_BROADCAST="192.168.0.255"
FAKE_IP="192.168.254.1"
FAKE_BROADCAST="192.168.254.7"
#FAKE_IFACE="eth0:0"
LO_IFACE="lo"
LO_IP="127.0.0.1"
IPTABLES="/sbin/iptables"
/sbin/depmod -a
/sbin/modprobe ip_tables
/sbin/modprobe ip_conntrack
/sbin/modprobe iptable_filter
/sbin/modprobe iptable_mangle
/sbin/modprobe ipt_LOG
/sbin/modprobe ipt_limit
/sbin/modprobe ipt_state
/sbin/modprobe iptable_nat
echo "1" > /proc/sys/net/ipv4/conf/all/rp_filter
$IPTABLES -P INPUT DROP
$IPTABLES -P OUTPUT DROP
$IPTABLES -P FORWARD DROP
$IPTABLES -N bad_tcp_packets
$IPTABLES -N allowed
$IPTABLES -N tcp_packets
$IPTABLES -N udp_packets
$IPTABLES -N icmp_packets
$IPTABLES -A bad_tcp_packets -p tcp --tcp-flags SYN,ACK SYN,ACK -m state --state NEW -j REJECT --reject-with tcp-reset
$IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j DROP
$IPTABLES -A allowed -p TCP --syn -j ACCEPT
$IPTABLES -A allowed -p TCP -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A allowed -p TCP -j DROP
$IPTABLES -A tcp_packets -p TCP -s $REAL_IP/32 -d $REAL_IP/32 -j allowed
$IPTABLES -A tcp_packets -p TCP -s $FAKE_IP/32 -d $FAKE_IP/32 -j allowed
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j ACCEPT
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 11 -j ACCEPT
$IPTABLES -A INPUT -p ALL -d $REAL_IP -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A INPUT -p TCP -i $REAL_IFACE -j tcp_packets
$IPTABLES -A INPUT -p UDP -i $REAL_IFACE -j udp_packets
$IPTABLES -A INPUT -p ICMP -i $REAL_IFACE -j icmp_packets
$IPTABLES -A INPUT -p ALL -d $FAKE_IP -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A INPUT -p TCP -i $FAKE_IFACE -j tcp_packets
$IPTABLES -A INPUT -p UDP -i $FAKE_IFACE -j udp_packets
$IPTABLES -A INPUT -p ICMP -i $FAKE_IFACE -j icmp_packets
$IPTABLES -A OUTPUT -p ALL -s $LO_IP -j ACCEPT
$IPTABLES -A OUTPUT -p ALL -s $REAL_IP -j ACCEPT
$IPTABLES -A OUTPUT -p ALL -s $FAKE_IP -j ACCEPT
#$IPTABLES -t nat -A POSTROUTING -s 192.168.254.0/29 -o eth0 -j SNAT --to-source 192.168.0.1
$IPTABLES -t nat -A POSTROUTING -s 192.168.254.2 -o eth0 -j SNAT --to-source 192.168.0.1