Dynamic Nat is useful in a larger network where one public IP is not sufficient to fulfill the requirement of an organization. In the Dynamic Nat, we can create a pool of public IP addresses that will be used for the NAT translations.
Large organizations can have thousands to devices that require access to the public network like internet but just having one public IP address cannot fulfill the need of all the devices as users may generate too many request at the same time, which cannot be fulfilled by using single IP address even using PAT.
Dynamic Nat is same as the normal Nat – the only difference is that the Dynamic Nat uses a pool of public IP addresses for the Nat translation. And the IP addresses from the pool are dynamically selected for the translation.
Dynamic Nat allows organizations with huge number of network devices to access internet without any congestion issue and devices will perform smoothly as they will be selecting random public IP address from the pool to communicate with the outer network.
One best example of dynamic NAT is our home router, our ISP only gives 1 public IP but when we use router, we are able to access internet on multiple devices. This is only possible when our router performs network address translation and assign private IP addresses to the internal network but when our device communicate with the internet, it translates our private address to public address.
Normally, we do not configure our home router with NAT because it is already configured by the manufactures as that is the sole purpose of the home router and common people do not have any technical knowledge, so they want ready to use device that can be used to share the internet connection between multiple users.
We have to label the router interface with IP Nat inside and IP Nat outside, and create an access list to permit a range of IPs to be translated. Then, we have to create a pool of public IP addresses, which are given by the ISP. And finally, we have to allow the private IPs to be translated dynamically with the pool of public IP addresses. To enable Pat with the Dynamic Nat, we have to type ‘overload’ at the end.
Dynamic NAT configuration commands
1. label the interfaces
2. create a access list to allow network 192.168.1.0/24 to be translated
3. create a pool of public IP addresses from 188.8.131.52 to 184.108.40.206
4. Enable NAT with PAT
Router(config)#interface fastethernet 0/0
Router(config)#ip nat inside
Router(config)#interface fastethernet 0/1
Router(config)#ip nat outside
Router(config)#access-list 1 permit 192.168.1.0 0.0.0.255
Router(config)#ip nat pool public-ips 220.127.116.11 18.104.22.168 netmask 255.255.255.0
Router(config)#ip nat inside source list 1 pool public-ips overload