What is Dynamic NAT and How to Configure Dynamic NAT in Cisco Router

What is Dynamic NAT

Dynamic NAT uses the public addresses in the pool and from the pool, the public IP addresses are assigned to hosts on a first-come-first-served basis. When a host request access to the Internet with a private address then from the pool the dynamic NAT choose an IP address and assign it to the requested host which is not already used by another host.

The connections in dynamic NAT are established from within the private network out to the public network. When the connection of outbound is made then a pool of network addresses is used and maintained. A unique public IP address is assigned to each connection. The simultaneous connection maximum numbers in the pool are equal to the number of public addresses. Through a dynamic NAT, the dynamic NAT allows you to communicate with the Internet.

How to Configure Dynamic NAT

How to Configure Dynamic NAT in Cisco Router

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 8.0.0.1 255.0.0.0

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 8.0.0.2 255.0.0.0

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 R1 and ISP R2 Routing Table

Router R1

R1# show ip route

IP Route Status

R1#

ISP Router R2

R2# show ip route

IP Route Status

R2#

Completing Routing Tables of Routers using RIP

Router R1

R1# configure terminal

R1 (config) #router rip

R1 (config-router) #version 2

R1 (config-router) #network 192.168.1.0

R1 (config-router) #network 8.0.0.0

R1 (config-router) #end

R1#

ISP Router R2

R2# configure terminal

R2 (config) #router rip

R2 (config-router) #version 2

R2 (config-router) #network 192.168.2.0

R2 (config-router) #network 8.0.0.0

R2 (config-router) #end

R2#

Router R1 and ISP R2 Routing Table

Router R1

R1# show ip route

IP Route Status

R1#

ISP Router R2

R2# show ip route

IP Route Status

R2#

Defining the Dynamic NAT on Router R1

R1# configure terminal

R1 (config) #

Creating Source List using ACL (Access List)

R1 (config) # access list 15 permit 192.168.1.1

R1 (config) # access list 15 permit 192.168.1.2

R1 (config) # access list 15 permit 192.168.1.3

R1 (config) # access list 15 permit 192.168.1.4

Configuring the Dynamic NAT on Router R1

R1 (config) #ip nat pool Networking 8.0.0.3 8.0.0.6 netmask 255.0.0.0

R1 (config) #ip nat inside source list 15 pool Networking

R1 (config) #

Applying Dynamic NAT on Router R1

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 on Router R1

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 PC1

PC 1> ping 192.168.2.1

Successful Ping

Note: After pings the destination IP address from PC 1 and opening the Router R1, then it will show as follows after IP NAT debugging on command in the Privileged Mode.