That is it will follow Hub and spoke topology ;

That is VPC4=10.4.0.0/16 will act as Hub ; and the rest of VPC will be Spok

For example VPC1 =10.1.0.0/16 will be spoke

VPC2= 10.2.0.0/16 wil be spoke

VPC3=10.3.0.0/16 will be spoke.

So after we finish all EC2 instance in each VPC will be able to talked to each other.

Step 1) We will need to create a VPC1=10.1.0.0/16 and also create IGW and attached to VPC1;Then we will create public Subnet 10.1.1.0/24 in Subnet 1

As we see when I created VPC 1 =10.1.0.0/16 , the AWS has created a Routing table for me ;lets give the Name “ This was created by system when I created a VPC 10.1.0.0/16

Step 2) I need to create a new Custom RT ;and call it “ Public Routing table for 10.1.0.0/16” goes to internet ; then add entry to 0.0.0.0 and point to IGW that was called “VPC1 IGW”

Step 3) Remember make sure go to Subnet Association and associate Subnet 10.1.1.0/24 ; with above Custom Routing Table.

Step 4) I will do same concept for :

VPC 2 = 10.2.0.0/16

Public Subnet = 10.2.1.0/24

Create an IGW VPC2 ; and attached to VPC2

Created a new RT for VPC 2

Subnet Association

Step 5) I will need to do above task for :

VPC 3 = 10.3.0.0/16

Public Subnet = 10.3.1.0/24

Create an IGW VPC3 ; and attached to VPC3

Created a new RT for VPC 3

Subnet Association

Step 6) Now I will go to EC2 and I will bootup an Amazon Linux AMI and put on each corresponding Subnet and each corresponding VPC ;

Lets called it as follow :

PC1-10.1.0.0 ( put inside VPC1 , subnet 10.1.1.0/24)

PC2-10.2.0.0 ( put inside VPC2 , subnet 10.2.1.0/24)

PC3-10.3.0.0 ( put inside VPC3 , subnet 10.3.1.0/24)

Step 7) Now in order each EC2 talked to each other I need to do VPC peering; that is

VPC1 peer with VPC2 and VPC2 peer with VPC 3 and remember we do not have transitive Peering so VPC1 cannot talk to VPC3 , so in order to do this I need to have another VPC peering between VPC1 and VPC3

As we see this will get harder as we get more VPC , so in order to solve the problem Amazon came with Transit Gateway

Step 8) Now I will start my actual Lab in here

Step 9) I go in top ; then click on VPC; then on right side I go to transit gateway

Step 10) Lets create it and I will call it :

Name: ASMTransitgateway

Description : This will be used for VPC1 , and VPC2, and VPC3

Step 10) Give AS for BGP = 64512 and rest of value leave as default

Step 11) Now I will to go and attached VPC1, VPC2 and VPC3 to above transit gateway

Step 12) Go to left and click transit gateway attachment ; then pick VPC1 and give name VPC1 and pick Public Subnet 1

Step 13) Do same concept for VPC2 , and VPC 3 and after 5 ins you should get all VPC available

Step 14) Now when all is good on step13 ; when I go to left and look at transit gateway routing table I will see all the routes from VPC1,VPC2,VPC3 in here , so route has been propagated in here

Step 15) Now if I SSH to EC2 lcoated in VPC 1 ( 10.1.0.0/24) I will not be able to ping an EC2 located on 10.2.1.x or 10.3.1.X Why ? Since remember I need to go to each Routing table of VPC1, and VPC2 and VPC 3 add a corresponding Route and point to transit gateway.

Step 16) that is I need to have this

For VPC1 :

10.1.0.0/16 local

0.0.0.0/0 IGW

10.2.0.0/16 transit gateway ( I need to add this entry )

10.3.0.0/16 transit gateway ( I need to add this entry)

For VPC2 :

10.2.0.0/16 local

0.0.0.0/0 IGW

10.1.0.0/16 transit gateway ( I need to add this entry )

10.3.0.0/16 transit gateway ( I need to add this entry)

For VPC3 :

10.3.0.0/16 local

0.0.0.0/0 IGW

10.1.0.0/16 transit gateway ( I need to add this entry )

10.2.0.0/16 transit gateway ( I need to add this entry)

Step 17) Now I will SSH to EC2 on VPC1 = that is 10.1.1.x network and I should be able to ping VPC2 = 10.2.1.x and VPC3=10.3.1.x

Step 18) As we see now all EC2 can talk to each other ; so the key to remember when you create transit gateway and attached to the VPC; it will learn all routes from VPC1 , VPC2, and VPC3 , and make sure you go to corresponding Routing table of VPC1, VPC2 and VPC 3 and update the routing table . Make sure delete all Transit Gateway in order not to get charged.