Configuration of Dynamic NAT

Step by Step Configuration 

With dynamic NAT, you must manually define two sets of addresses on your address translation device. One set defines which inside addresses are allowed to be translated (the local addresses), and the other defines what these addresses are to be translated to (the global addresses).

In this example our internal network is using 192.168.0.0 network. We have five public ip address 50.0.0.1 to 50.0.0.5 to use. Router1(1841 Router0) is going to be NAT device. Double click on Router1(1841 Router0) and configure it as given below

Router>enable
Router#configure terminal
Router(config)#hostname R1
R1(config)#interface fastethernet 0/0
R1(config-if)#ip address 192.168.0.1 255.0.0.0
R1(config-if)#no shutdown
R1(config-if)#exit
R1(config)#interface serial 0/0/0
R1(config-if)#ip address 30.0.0.1 255.0.0.0
R1(config-if)#clock rate 64000
R1(config-if)#bandwidth 64
R1(config-if)#no shutdown
R1(config-if)#exit
R1(config)#ip route 0.0.0.0 0.0.0.0 serial 0/0/0
R1(config)#access-list 1 permit 192.168.0.0 0.0.0.255
R1(config)#ip nat pool test 50.0.0.1 50.0.0.5 netmask 255.0.0.0
R1(config)#ip nat inside source list 1 pool test
R1(config)#interface fastEthernet 0/0
R1(config-if)#ip nat inside
R1(config-if)#exit
R1(config)#interface serial 0/0/0
R1(config-if)#ip nat outside
R1(config-if)#exit
R1(config)#exit

Now double click on R2(1841 Router1) and configure it as given below

Router>enable
Router#configure terminal
Router(config)#interface fastEthernet 0/0
Router(config-if)#ip address 20.0.0.1 255.0.0.0
Router(config-if)#no shutdown
Router(config-if)#exit
Router(config)#interface serial 0/0/0
Router(config-if)#ip address 30.0.0.2 255.0.0.0
Router(config-if)#no shutdown
Router(config-if)#exit
Router(config)#ip route 0.0.0.0 0.0.0.0 serial 0/0/0
Router(config)#hostname R2
For testing of NAT go R1 and enable debug for NAT from privilege mode

R1#debug ip nat 
Now go on pc5  and ping to 20.0.0.2
When ICMP ping packet reach to R1. It examines its source address against the access list 1. As this packet is generated form the network of 192.168.0.0 so it will pass the access list. Now router will check NAT pools for free address to translate with this address. Which you can check in the output of debag command in R1
IP NAT debugging is on
NAT: s=192.168.0.7->50.0.0.1, d=20.0.0.2[1]
NAT*: s=20.0.0.2, d=50.0.0.1->192.168.0.7[1]
NAT: s=192.168.0.7->50.0.0.1, d=20.0.0.2[1]
NAT*: s=20.0.0.2, d=50.0.0.1->192.168.0.7[1]
NAT: s=192.168.0.7->50.0.0.1, d=20.0.0.2[1]
NAT*: s=20.0.0.2, d=50.0.0.1->192.168.0.7[1]
NAT: s=192.168.0.7->50.0.0.1, d=20.0.0.2[1]
NAT*: s=20.0.0.2, d=50.0.0.1->192.168.0.7[1]
As you can see in output 192.168.0.5 is translate with 50.0.0.1 before leaving the router.
In real life its best practices to turn off debug after testing so go on Router 1 and turn off debug mode.
R1#no debug ip nat IP NAT debugging is off R1# 

To configure static NAT

Follow this step by step static NAT configure

Configure ip address on PC and Server as given in figure

Now configure R1 exactly given here

Router>enable
Router#configure terminal
Router(config)#hostname R1
R1(config)#interface fastethernet 0/0
R1(config-if)#ip address 10.0.0.1 255.0.0.0
R1(config-if)#no shutdown
R1(config-if)#exit
R1(config)#interface serial 0/0/0
R1(config-if)#ip address 20.0.0.2 255.0.0.0
R1(config-if)#no shutdown
R1(config-if)#exit
R1(config)#ip route 30.0.0.0 255.0.0.0 20.0.0.1
R1(config)#ip nat inside source static 10.0.0.2 50.0.0.1
R1(config)#interface fastEthernet 0/0
R1(config-if)#ip nat inside
R1(config-if)#exit
R1(config)#interface serial 0/0/0
R1(config-if)#ip nat outside
R1(config-if)#exit
R1(config)#

Now configure R0 exactly given here

Router>enable
Router#configure terminal
Router(config)#hostname R0
R0(config)#interface fastethernet 0/0
R0(config-if)#ip address 30.0.0.1 255.0.0.0
R0(config-if)#no shutdown
R0(config-if)#exit
R0(config)#interface serial 0/0/0
R0(config-if)#ip address 20.0.0.1 255.0.0.0
R0(config-if)#clock rate 64000
R0(config-if)#bandwidth 64
R0(config-if)#no shutdown
R0(config-if)#exit
R0(config)#ip route 50.0.0.0 255.0.0.0 20.0.0.2
R0(config)#
As you have seen in configuration there is not direct route for 10.0.0.2. So PC from network of 30.0.0.0 will never know about it. They will access 50.0.0.1 as the web server IP. To test it double click on any computer and ping from 50.0.0.1 and you will get replay.
Packet Tracer PC Command Line 1.0
PC>ping 50.0.0.1
Pinging 50.0.0.1 with 32 bytes of data:
Reply from 50.0.0.1: bytes=32 time=141ms TTL=126
Reply from 50.0.0.1: bytes=32 time=80ms TTL=126
Reply from 50.0.0.1: bytes=32 time=109ms TTL=126
Reply from 50.0.0.1: bytes=32 time=125ms TTL=126

Ping statistics for 50.0.0.1:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 80ms, Maximum = 141ms, Average = 113ms
Now ping from 10.0.0.2 and you will get destination host unreachable error.
PC>ping 10.0.0.2
Pinging 10.0.0.2 with 32 bytes of data:
Reply from 30.0.0.1: Destination host unreachable.
Reply from 30.0.0.1: Destination host unreachable.
Reply from 30.0.0.1: Destination host unreachable.
Reply from 30.0.0.1: Destination host unreachable.

Ping statistics for 10.0.0.2:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss)