Rafat Khandaker

Packet Tracer

NAT PROTOCOL

05-13-16

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ABSTRACT

This is a brief configuration to configure NAT protocol on Cisco Routers. A simple simulation has been configured to allow hosts from an "inside" private network to access a server through its public IP address.

INTRODUCTION

NAT, the acronym for "Network Address Translation," is a protocol designed to separate private ip address from public ip address. Often times, when connecting to a website or asking the dns server to translate web host to an ip address, we will see an external public IP address assigned to the host. To test NAT, personally, you can go on your computer

(for windows)

type window key + r, or go to search;

type cmd to open command prompt,

then type ipconfig

(for mac and linux)

open a terminal and type

ifconfig

you will notice that your ip address on the internal network is ( 192.168.1...... or 10.10...... )

now go to google and type: what is my ipv4 address ?

you will notice that your public ip address is different from your local.

This is because google can only see the ip address of your router's external port.

The reason the two addresses are different is because your router is configured with a public ip address, while your internal network is configured with private ip address. Private ip addresses can be used over and over again in different networks but they are translated with a different network address on its external interface. NAT is a protocol that routers and servers use to transition public to private ip address within a network.

The protocol was designed in an attempt to save ipv4 addresses in the internet. With NAT, the ip

address space are unrestricted to both private and public networks.

Along with NAT, PAT is used to translate ports to network address. Often times, a user will connect outside to the internet, into different websites. Websites will use multiple users into port 80 and redirect a stable connection into a range of TCP/UDP session ports. When a connection is stable it cannot use the same port that is already occupied. port 80 is a default web port, often times is redirected into a different TCP/UDP port to establish a connection.

SIMULATION

RESEARCH CISCO COMMAND INTERFACE

RESOURCE: https://www.youtube.com/watch?v=xkCgYaJXDSk

NAT can be assigned

MY CONFIGURATION FOR THE SIMULATION

ROUTER 0

So for the router connected to the server, I configured a static NAT with PAT.

I decided to use Rip v2 to exchange routing table. ( I could have used EIGRP or OSPF or static but for simplicities sake )

statically assigned to serve one web host.

ROUTER 1

Router 1 is dynamically configured because I wanted to allow multiple private ip to access the network. Pat and access list is configured to allow internal hosts to access the network, vice versa.

accessing the website through its public IP address from an internal host

CONCLUSION:

This was a simple configuration, demonstrating how NAT can be used to translate private network address.