Nat (network address translation)



Network address translation (nat) is a method of remapping an ip address space into another by modifying network address information in the ip header of packets while they are in transit across a traffic routing devices. The technique was originally used to avoid the need to assign a new address to every host when a network was moved, or when the upstream internet service provider was replaced, but could not Route the network address space. It has become a popular and essential tool in conserving global address space in the face of ipv4 address exhaustion. One internet routable IP address of a NAT gate way can be used for an entire private network.

Ip masquerading is a technique that hides an entire IP address space, usually consisting of private IP addresses, behind a single IP address in another, usually public address space.
The hidden addresses are changed into a single (public) IP address as the source address of the outgoing IP packets so they appear as originating not from the hidden host because of the popularity of this technique to conserve ipv4 address space, the term NAT has become virtually synonymous with IP masquerading.

As network address translation modifies the ip address information in packets, NAT implementation may very in their specific behaviour in various addressing case and their effect on network traffic. The specific of NAT behavior are not commonly documented by vendors of equipment containing NAT implementation.

(Network address translation)

NAT is method of translation of private IP address into public IP address.

What is private IP address:-

Which is free to use but not work on internet is called private IP address the range is following types

Class A    

Class B 

Class C

Nat is act as middle man between private IP address and public IP address. It is convert the packet which come from private IP address and provide header footer of public IP address.

Basic NAT



The simplest type of NAT provide a one to one translation of IP addresses. RFC 2663 refers to this type of NAT as basic nat it is also called a one NAT. In this type of NAT, only the IP addresses, IP header checksum and any higher level checksum that include the IP address are changed. Basic NAT can be used to interconnect two IP network that have incompatible addressing.

Dynamic NAT (network address translation)

Dynamic NAT, just like static NAT, is not common in smaller network but is found within larger corporations with complex networks. The way dynamic nat differs from static NAT is that where static NAT provides a one to one internal to public static IP address mapping, dynamic NAT usually uses a group of available public IP addresses.

What is inside NAT and outside NAT

Inside NAT:-

This is the private IP address range use in the private network is called inside NAT or inside global.

Outside NAT:-

This is public IP address use in public network it is called outside NAT or outside global.

Type of NAT

Static NAT:-

In this process there is one to one mapping done manually generally use when we required every private IP address one register IP address (1 to 1 basis)


Lab of static NAT:-

We want to configure the static NAT using the following translatio

Configure this lab with IP and perform in static routing.

R1(config)#ip route

R2(config)#ip route

After that configuration static NAT on R1 route

R1(config)#ip nat inside source static

R1(config)#ip nat inside source static

R1(config)#ip nat inside source static

R1(config)#ip nat inside source static


R1(config)#int s1/0

R1(config-if)# ip nat outside
After that from the pc ping to and then use the command on R1


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