In this article we will discuss about NAT – Network Address Translation. The Address Translation is the most important part of IPv4 addressing. Almost all home and business organization routers use Network Address Translation. In fact IPv4 address would not survive this long without NAT. Because we all use private internet addresses on our home networks or local area networks, and those private addresses are not routable across the internet.
Addresses started with 192.168.X.X, or 10.X.X.X, or 172.16.X.X are all private addresses according to private addressing RFC 1918. It says addresses within this ranges are private addresses and therefore these addresses are not routable across the internet. So if we need to use these addresses in our LAN then when it crosses the router it must be translated or Network Address Translated to a public address. Therefore almost all router do it if running IPv4 network which is most of the router in IPv4 Network. So IPv4 survived for private addressing and Network Address Translation, also because of classless addressing or CIDR.
NAT | Network Address Translation
Certainly all available public IPv4 addresses are not enough for all devices on the internet. Therefore to prevent the shortage of public IPv4 addresses engineers developed private address and address translation. However all devices in LAN are assigned private addresses by router. ON the other hand ISP provides a public IP address for the router. But a device to access internet it must need a public IP address. So NAT in the router translate the private IP address of that particular device into public address when it needs to access internet. Then the Router stores the device information in NAT_table in its memory to forward the requested data to that particular device (translating public_address to private_address again) when it arrives.
Routers that we use in our home or small office can do Network addressing automatically. But in CISCO CCNA we require to know how to configure NAT for particular devices and services in the network.
NAT_Configuration for CISCO Routers
There are different types of NAT configurations:
1. Static Translation 1-to-1
2. Port Address Translation 1-to-1 Port 80
3. NAT Overload Translation, also known as PAT
4. Dynamic Translation (NAT_Pool)
In the video lectures below provide detail information about how to configure all these kind of Network Address Translation for CISCO Routers .
Lecture – 1
Lecture – 2
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