CCNA NAT Configuration with PAT

PAT - Port Address translation. We use PAT in that condition when we have few Public IP & hundreds of inside local address need to translate. Pat use port numbers in transport layer to identify hosts. can translate up to 65,000 hosts with one real IP.Sometimes we called this overload operation also.

In this example the internal network using 30.0.0.0 network.we will use one public ip 50.0.0.1.

Router(config)#hostname R0
R0(config)#enable secret open
R0(config)#int fa
R0(config)#int fastEthernet 0/1
R0(config-if)#ip add
R0(config-if)#ip address 30.0.0.1 255.0.0.0
R0(config-if)#no shut

R0(config-if)#exit

R0(config)#int serial 2/0

R0(config-if)#ip add
R0(config-if)#ip address 20.0.0.1 255.0.0.0
R0(config-if)#no shut

R0(config)#ip route 0.0.0.0 0.0.0.0 serial 2/0

R0(config)#access-list 1 permit 30.0.0.0 0.0.0.255
R0(config)#ip nat pool test 50.0.0.1 50.0.0.1 netmask 255.0.0.0
R0(config)#ip nat inside source list 1 pool test overload

R0(config)#int fastEthernet 0/1
R0(config-if)#ip nat inside
R0(config-if)#exit
R0(config)#int serial 2/0
R0(config-if)#ip nat outside
R0(config-if)#exit
R0(config)#exit

Now goto R1 Router

Router(config)#hostname R1
R1(config)#enable secret open

R1(config)#int fastEthernet 0/0
R1(config-if)#ip address 10.0.0.1 255.0.0.0
R1(config-if)#no shut

R1(config-if)#exit

R1(config)#int serial 2/0

R1(config-if)#ip address 20.0.0.2 255.0.0.0
R1(config-if)#no shut

R1(config)#ip route 0.0.0.0 0.0.0.0 serial 2/0

Now ping from all host  PC to server(10.0.0.2) and goto R0 Router and apply below command.We can see port numbers with below report.

R0#sh ip nat translations
Pro  Inside global     Inside local       Outside local      Outside global
icmp 50.0.0.1:1024     30.0.0.2:1         10.0.0.2:1         10.0.0.2:1024
icmp 50.0.0.1:1025     30.0.0.2:2         10.0.0.2:2         10.0.0.2:1025
icmp 50.0.0.1:1026     30.0.0.2:3         10.0.0.2:3         10.0.0.2:1026
icmp 50.0.0.1:1027     30.0.0.2:4         10.0.0.2:4         10.0.0.2:1027
icmp 50.0.0.1:1        30.0.0.3:1         10.0.0.2:1         10.0.0.2:1
icmp 50.0.0.1:2        30.0.0.3:2         10.0.0.2:2         10.0.0.2:2
icmp 50.0.0.1:3        30.0.0.3:3         10.0.0.2:3         10.0.0.2:3
icmp 50.0.0.1:4        30.0.0.3:4         10.0.0.2:4         10.0.0.2:4

                                                                               ——————– Thanks Everyone