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NAT Gateway In AWS

This article describes the NAT gateway in AWS.

What Is NAT Gateway?

NAT (stands for Network Address Translation) is a service that allows the EC2 instance in the private subnet to connect to the internet.

How To Create A NAT Gateway?

To create the NAT Gateway, we will work on the following steps: -

Create a private subnet
Create a new route table
Associate the subnet with the route table
Launch two EC2 Linux instances
Enable OpenSSH Authentication Agent service
Log in to the Linux instance using the SSH utility
Ping Google
Create a NAT gateway
Add an entry of NAT gateway in the route table
Ping Google again

So, let us get started.

Create A Private Subnet

To begin with, create a subnet. As the subnet should be private, the property Auto-assign public IPv4 address is set to No.

Picture showing the private subnet created in AWS console

Click to Enlarge

Create A New Route Table

The next step is to create a new route table. Please note that there should be no route for an internet gateway.

Picture showing a new route table created in AWS console

Click to Enlarge

Associate The Subnet With The Route Table

The next step is to associate the subnet with the route table.

Picture showing associating the route table with private network

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Launch Two EC2 Linux Instances

Launch two EC2 instances, one in private and the other in public.

Picture showing the 2 Linux EC2 instances created in AWS console

Click to Enlarge

Enable Openssh Authentication Agent Service

Go to services.msc and change the Start type as Manual.

Picture showing changing the Openssh Authentication Agent Service startup type as Manual

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Open the command prompt and write the following command: -

ssh-agent.exe

Log In To The Linux Instance Using SSH Utility

To begin with, write the following command: -

ssh-add -k karan.pem

In the above command, karan.pem is the private key file name. The purpose of the above command is to add the private key to the SSH authentication agent.

Picture showing the ssh-add command for adding the private key in SSH authentication agent

Click to Enlarge

To connect to the EC2 instance in a public subnet, write the following command: -

ssh -A ec2-user@<Public IP address of EC2 instance>

Picture showing connecting the Linux virtual machine using ssh utility

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Once the EC2 instance is connected, connect to the other EC2 instance (which was launched in a private subnet). Use the following command: -

ssh ec2-user@<Private IP of EC2 instance>

Picture showing connecting to second EC2 instance using SSH utility

Click to Enlarge

Ping Google

Now, the EC2 instance launched in the private subnet is connected, write the following command to ping Google.

ping google.com

You cannot ping because the subnet is private and not connected to the Internet.

Picture showing the error when pinging Google.com

Click to Enlarge

Create A NAT Gateway

To create a NAT gateway, click the NAT Gateways menu in the VPC dashboard.

Picture showing the NAT Gateways menu in VPC dashboard

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A screen will appear on the right-hand side. Click the Create NAT gateway button.

Picture showing the Create NAT gateway button for adding the new NAT Gateway

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In the Create NAT gateway screen, enter the following information: -

Field	Value
Name	Any custom name of the NAT gateway.
Subnet	Select the Public subnet.
Elastic IP allocation ID	Select the elastic IP. If an elastic IP does not exist, then click on the “Allocate Elastic IP” button to create it.

Picture showing the screen to create NAT Gateway

Click to Enlarge

Scroll down to the bottom and click the Create NAT gateway button. The NAT gateway is created.

Add An Entry Of NAT Gateway In The Route Table

Add a route entry of NAT gateway in the private route table.

Picture showing the screen to add network gateway as route in route table

Click to Enlarge

Ping Google Again

Once more, ping Google; you will find that you can ping Google this time.

Picture showing the ping to Google successfully

Click to Enlarge

Posted By -	Karan Gupta

Posted On -	Wednesday, July 27, 2022

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