Network Address Translation (NAT)

Hello guys,
Thank God its Friday!!! Today, we are gonna talk about Network Address Translation (NAT). NAT is  feature used primarily with IPv4 whose purpose is to help conserve IP address so we do not run out of them,as well as provide network security by hiding the internal addresses from the internet users. As we know,well its ok if you don’t know cos am gonna tell you anyway, IPv4 provides for 4.2 billion addresses. That’s huge. Isn’t it? Well, not when you know that the world population clocked 7 billion some years ago.

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Ipv4 does not provide for the needed addresses required by everyone who desires internet access. More worrisome is the fact that a single individual now has up to 5 IP gadgets to him/herself.
To solve this problem, NAT was introduced. NAT allows two or more network hosts to use different private addresses and be translated to one public address as they make their way to the internet. IP address blocks from the three main classes ( classes A,B, and C) have been reserved for private use. These addresses are 10.0.0.0 – 10.255.255.255 for class A, 172,16.0.0 – 172.31.255.255 for class B, and 192.168.0.0 – 192.168.255.255 for class C. You can use any of these addresses on your LAN but to access the internet, you need to have NAT configured. Follow the steps below to configure NAT on a cisco router:

Router(config)#ip nat pool cisco 197.255.255.1 197.255.255.1 netmask 255.255.255.252 (the public IP on your WAN interface given to you by your ISP)
Router(config)#ip nat inside source list 1 pool cisco overload (overload because you NAT many private IPs to one or few pubic IPs)
Router(config)#access-list 1 permit 192.168.1.0 0.0.0.255(access-list matches the private IPs to NAT)
Router(config)#int f0/0 (your LAN interface)
Router(config-if)#ip nat inside
Router(config-if)#int f0/1 (your WAN interface)
Router(config-if)#ip nat outside
Router(config-if)#exit
Router(config)#copy run start (dont forget to save)

I hope this helps.