Port Address Translation (PAT) Configuration

What is Port Address Translation

NAT overloading sometimes called Port Address Translation (PAT) which maps the multiple addresses of private IP into a few addresses or to a single IP address. To do this, through the port number each private IP address is also tracked, and from outside when a response comes back, to which client the NAT router translates the packets which are determined through the port numbers.

PAT is the NAT extension that on the LAN (Local Area Network) permits multiple devices to be mapped into a single public IP address. It is used almost in home networks, and a single IP address is assigned to the home network’s router through the ISP (Internet Service Provider).

The client port number is assigned by the router when Y computer logs on the Internet which is appended to the internal IP address. This gives a unique IP address to the Y computer in effect, if the internet logs the Z computer at the same time, the same local IP address with a different port number is assigned by the router. Although at the same time both computers Y and Z are accessing the internet and sharing the same public IP address, which computer to send specific packets to exactly the router knows because each computer has a unique internal address.

Port overloading, port-level multiplexed NAT, porting, and single address NAT is called the Port Address Translation (PAT).

Port Address Translation Configuration

PAT Configuration With Packet Tracer

Configuring the Router R1 Interfaces

Router> enable

Router# configure terminal

Enter configuration commands, one per line. End with CNTL / Z.

Router (config) # hostname R1

R1 (config) # interface serial 0/1/0

R1 (config-if) # ip address 4.0.0.6 255.0.0.0

R1 (config-if) #clock rate 64000

R1 (config-if) #keepalive 10

R1 (config-if) #no shutdown

%LINK-5-CHANGED: Interface Serial0/1/0, changed state to down

R1 (config-if) #exit

R1 (config) # interface fastethernet0/0

R1 (config) # int fa0/0

R1 (config-if) # ip address 192.168.1.15 255.255.255.0

R1 (config-if) #no shutdown

Interface Status up

R1 (config-if) #end

R1#

Configuring the ISP Router R2 Interfaces

Router> enable

Router# configure terminal

Enter configuration commands, one per line. End with CNTL / Z.

Router (config) # hostname R2

R2 (config) # interface serial 0/1/0

R2 (config-if) # ip address 4.0.0.7 255.0.0.0

R2 (config-if) #keepalive 10

R2 (config-if) #no shutdown

Interface Status up

R2 (config-if) #exit

R2 (config) # interface fastethernet0/0

R2 (config) # int fa0/0

R2 (config-if) # ip address 192.168.2.15 255.255.255.0

R2 (config-if) #no shutdown

Interface Status up

R2 (config-if) #end

R2#

Router R1and ISP R2 Routing Table

Router 1

R1# show ip route

IP Route Status

R1#

ISP Router 2

R2# show ip route

IP Route Status

R2#

Completing Routing Tables of Routers

Router 1

R1# configure terminal

R1 (config) #ip route 192.168.2.0 255.255.255.0 4.0.0.7

R1 (config) #end

R1#

ISP Router 2

R2# configure terminal

R2 (config) #ip route 192.168.1.0 255.255.255.0 4.0.0.6

R2 (config) #end

R2#

Router R1 and ISP R2 Routing Table

Router 1

R1# show ip route

IP Route Status

R1#

ISP Router 2

R2# show ip route

IP Route Status

R2#

Defining the Dynamic NAT on Router 1

R1# configure terminal

R1 (config) #

Creating Source List using ACL (Access List)

R1 (config) # access-list 30 permit 192.168.1.0 0.0.0.255

Configuring the Dynamic NAT on Router R1

R1 (config) #ip nat inside source list 30 interface s0/1/0 overload

Applying Dynamic NAT on Router 1

R1 (config) #interface fastEthernet 0/0

R1 (config-if) #ip nat inside

R1 (config-if) #exit

R1 (config) #interface serial 0/1/0

R1 (config-if) #ip nat outside

R1 (config-if) #end

R1#

Verification

R1# show ip nat translations

Note: The NATTING table is empty, so there are no NAT translations still.

R1# debug ip nat

IP NAT debugging is on

Verification from PC

PC 3> ping 192.168.2.1

Successful Ping

Note: After pings the destination IP address from PC 3 and opening the Router R1, then it will show as follows after IP NAT debugging on command in the Privileged Mode.