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[wildweaselmi]

• This tutorial will detail the steps needed to properly configure network address translation (NAT) on a Cisco IOS router.
  
• Network Address Translation is a way for users on an internal network to share one or more external (often public) IP addresses.
  
• This tutorial will focus on the sharing of a single external IP address which is often referred to as port address translation (PAT).
  
• The following information is required for NAT:
  

  External IP address to be NAT'd: 99.99.99.99/24
  Internal IP address: 192.168.0.1/24

  

Running the commands in IOS
MyWiseGuys#config t
MyWiseGuys(config)#int fa0/0
MyWiseGuys(config-if)#ip add 192.168.0.1 255.255.255.0
MyWiseGuys(config-if)#no shut
MyWiseGuys(config-if)#int fa0/1
MyWiseGuys(config-if)#ip add 99.99.99.99 255.255.255.0
MyWiseGuys(config-if)#no shut
MyWiseGuys(config-if)#exit
MyWiseGuys(config)#access-1ist 1 permit 192.168.0.0 0.0.0.255
MyWiseGuys(config)#ip nat inside source list 1 interface fa0/1 overload
MyWiseGuys(config)#int fa0/0
MyWiseGuys(config-if)#ip nat inside
MyWiseGuys(config-if)#int fa0/1
MyWiseGuys(config-if)#ip nat outside
MyWiseGuys(config-if)#exit
MyWiseGuys(config)#exit
MyWiseGuys#copy runn start

c:\ping 192.168.0.1

c:\ping 99.99.99.99

MyWiseGuys#sh ip nat translations


show ip nat translations Field Descriptions
Pro = Protocol of the port identifying the address.
Inside global = The legitimate IP address that represents one or more inside local IP addresses to the outside world.
Inside local = The IP address assigned to a host on the inside network; probably not a legitimate address assigned by the Network Interface Card (NIC) or service provider.
Outside local = IP address of an outside host as it appears to the inside network; probably not a legitimate address assigned by the NIC or service provider.
Outside global = The IP address assigned to a host on the outside network by its owner.
create = How long ago the entry was created (in hours:minutes:seconds).
use = How long ago the entry was last used (in hours:minutes:seconds).
flags = Indication of the type of translation. Possible flags are:

• extended—Extended translation
  
• static—Static translation
  
• destination—Rotary translation
  
• outside—Outside translation
  
• timing out—Translation will no longer be used, due to a TCP finish (FIN) or reset (RST) flag.

Other related commands
clear ip nat translation
Clears dynamic NAT translations from the translation table.

ip nat
Designates that traffic originating from or destined for the interface is subject to NAT.

ip nat inside destination
Enables NAT of the inside destination address.

ip nat inside source
Enables NAT of the inside source address.

ip nat outside source
Enables NAT of the outside source address.

ip nat pool
Defines a pool of IP addresses for NAT.

ip nat service
Enables a port other than the default port.

show ip nat statistics
Displays NAT statistics.

Following attachment is from Cisco Systems (Verifying NAT Operation and Basic NAT Troubleshooting)
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