Dynamic Nat works well in a large network where one public IP is not sufficient to fulfill the requirement of an organization. In Dynamic Nat, we can create a pool of public IP addresses that will be used for the NAT translations.

Large organizations can have thousands of devices that require access to the public network like the internet but just having one public IP address cannot fulfill the requirement of all the devices as users may generate too many requests at the same time, which cannot be fulfilled with single IP address even using PAT.

Dynamic Nat is the same as static Nat – the only difference is that 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 a huge number of network devices to access the internet without any congestion issue and devices will perform smoothly as devices will be selecting a 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 a router, we can access the internet on multiple devices. This is only possible when our router performs network address translation and assigns private IP addresses to the internal network but when our device communicates with the internet, it translates our private address to a 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 users 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 use ‘overload’ at the end.

 

Dynamic NAT configuration commands

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Lab Tasks

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 117.45.23.2 to 117.45.23.5
4. Enable NAT with PAT

Lab Configuration

 Task 1

Router(config)#interface fastethernet 0/0

Router(config)#ip nat inside

Router(config)#interface fastethernet 0/1

Router(config)#ip nat outside

Task 2

Router(config)#access-list 1 permit 192.168.1.0 0.0.0.255

Task 3

Router(config)#ip nat pool public-ips 117.45.23.2 117.45.23.5 netmask 255.255.255.0

Task 4

Router(config)#ip nat inside source list 1 pool public-ips overload