#clear the rules table
iptables -F
iptables -t nat -F
iptables -t mangle -F
iptables -X

#set standard policity (what to do with packets not matching the folloiwng rules)
iptables -P INPUT REJECT


# Always accept loopback traffic
iptables -A INPUT -i lo -j ACCEPT

iptables -N block
iptables -A block -m state --state ESTABLISHED,RELATED -i ppp0 -d 192.168.0.0/32 -j ACCEPT
iptables -A block -m state --state ESTABLISHED,RELATED -o ppp0 -s 192.168.0.0/32 -j ACCEPT
iptables -A block -m state --state NEW,INVALID -i ! ppp0 -j ACCEPT
iptables -A block -j REJECT
iptables -A FORWARD -j block


# turn on NAT (IP masquerading for outgoing packets)
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE

#Enable routing.
echo 1 > /proc/sys/net/ipv4/ip_forward

# Disable response to ping. NO DDOS
/bin/echo "1" > /proc/sys/net/ipv4/icmp_echo_ignore_all

# Disable response to broadcasts.
# You don't want yourself becoming a Smurf amplifier.
/bin/echo "1" > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts

# Disable ICMP redirect acceptance. ICMP redirects can be used to alter your routing
# tables, possibly to a bad end.
/bin/echo "0" > /proc/sys/net/ipv4/conf/all/accept_redirects

iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -m state --state NEW -i ppp0 -j ACCEPT
iptables -A INPUT -d 192.168.0.0/24 -j ACCEPT