========================================== installed program ===========
apt-get install tcpdump
apt-get install nmap
apt-get install links
apt-get install less
apt-get install dnsutils
apt-get install mlocate

============================================ checking setting ==========
root@fu-manage:~# cat /proc/sys/net/ipv4/ip_forward 
root@fu-manage:~# echo 1 > /proc/sys/net/ipv4/ip_forward

<<<<<<< Defualt gateway  >>>>>>>
root@fu-manage:~# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         5.202.129.55    0.0.0.0         UG    0      0        0 eth1
5.202.129.0     0.0.0.0         255.255.255.0   U     0      0        0 eth1

------- ghable pak kardane defualt gateway age to ye shabake nistim bayad khodemono be gateway ezafe konim ---------
root@fu-manage:~#  ip route add 109.125.191.4 via 5.202.129.1
root@fu-manage:~#  ip route show
root@fu-manage:~#  ip route show | column -t

root@fu-manage:~# route del default

<<<<<<< iptables  >>>>>>>
root@fu-manage:~# iptables -t nat -L -nxv --line-numbers
root@fu-manage:~# iptables -t nat -D POSTROUTING 3


<<<<<<<  DNS >>>>>>>

root@fu-manage:~# cat /etc/bind/named.conf
root@fu-manage:~# rndc reload
============================================ save setting ==============
root@fu-manage:~# cat /etc/network/interfaces 

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
allow-hotplug eth1
iface eth1 inet static
	address 5.202.129.54
	netmask 255.255.255.0
	network 5.202.129.0
	broadcast 5.202.129.255
	gateway 5.202.129.1
	dns-nameservers 81.12.49.100
	dns-search fu-manage


root@fu-manage:~# cat /etc/rc.local 

iptables-save > iptablesload
root@fu-manage:~# cat /etc/network/if-pre-up.d/iptablesload
#!/bin/bash
iptables -t nat -F

iptables -t nat -A PREROUTING  -s 172.30.96.0/21 ! -d 5.202.129.54/32 -p tcp --dport 80 -j DNAT --to-destination 5.202.129.54:81 -m comment --comment "Tehran"
iptables -t nat -A PREROUTING  -s 172.30.0.0/16 ! -d 5.202.129.54/32 -p tcp -m tcp --dport 80 -j DNAT --to-destination 5.202.129.54:82 -m comment --comment "Shahrestan"
iptables -t nat -A PREROUTING  -s 172.30.0.0/16 -p udp -m udp --dport 53 -j DNAT --to-destination 5.202.129.54 -m comment --comment "DNS"

iptables -t nat -A POSTROUTING -s 172.30.0.0/16 -d 176.56.158.133/32 -p tcp -m tcp --dport 443 -m comment --comment "Bank Mellat" -j SNAT --to-source 5.202.129.54
iptables -t nat -A POSTROUTING -s 172.30.0.0/16 -d 212.80.25.14/32 -p tcp -m tcp --dport 443 -m comment --comment "Bank Parsian" -j SNAT --to-source 5.202.129.54

<<<<<<< net.ipv4.ip_forward=1 >>>>>>>
root@fu-manage:~# vi /etc/sysctl.conf
root@fu-manage:~# egrep -v '^#|^ *$' /etc/sysctl.conf
net.ipv4.ip_forward=1

root@fu-manage:~# sysctl -p /etc/sysctl.conf


========================================================================