AWS Networking

Study notes on Pluralsight AWSNetworking

web-vpc (VPC #1 Public VPC)


Name: web-vpc


Public subnet

Name: web-pub


Zone: us-east-1a

Internet Gateway

Go to the internet gateways tab and create

Name: web-igw

Attach to vpc: web-vpc

Route Table (aka “Implied Router”)

Each VPC has a default route table which is automatically associated with each subnet you create. All traffic into, out of and within a vpc traverses a implied router. It is the gatekeeper and the brains of vpc networking

Create a route table and associate it with a vpc

​ Name: web-pub,

​ select the vpc to associate it with

Associate subnet to route table

​ Now in vpc, go to subnet associations tab and associate subnet

​ Associated subnet: web-pub (

What this has done is that the aws has now assigned the “implied router” an ip address of (it always gets the first address in the subnet associated with the route table: in this case web-pub subnet)

So each vpc has a “pingable” implicit router.

Analogy to a traditional network: this is like when your internet service provider places an internet router at your site: they configure it for their site, and all you have to do is connect your network to it, which is what we are going to do now. We will connect our internet gateway to the implicit router by adding a route for our internet gateway.

  1. Go to route tables
  2. Select web-pub route
  3. Add route: Destination = Target: select internet gateway: web-igw

Idea here is that if our web server tries to send a packet to an ip address out on the internet, that destination will match the default route ( which means all destinations), and because the route table has the internet as the target, it will forward the packet via the internet gateway

Hence the analogy: creating a default route, pointing to the internet gateway is kind of like connecting to an ISP’s internet router to your network.

Launching an Instance

Security Group

Group name: web-pub-sg


Protocol/port Source

ssh (TCP/22) Your IP

HTTP (TCP/80) (all ips)

Elastic Network Interface (ENI) (network card)

Name: www1.eth0

Subnet: web-pub

IP Address:

Security group: web-pub-sg

Elastic IP (EIP)

Allocate new address (click)

Associate address (select)

Resource type: Network interface

Network interface: www1.eth0

Private ip: select only ip address from drop down

Launch Instance

Instances/Launch instance

Community AMIs: search for ami-1cb6b467 (this include docker )

Instance Type: t2.micro

Configure Details Tab:

  1. Network: web-vpc

  2. subnet: web-pub

  3. (ENI) Network Interfaces: eth0

    1. Network Interface: www1.eth0
ssh -i "pizza-keys.pem" ec2-user@

notice that the implicit router is first ip of the subnet:

#ping implicit router
#ping google to verify internet connectivity

#to see routes (not the vpc route table but the routes of the instance)

Note default route is . This is the implied router. Whenever instance wants to send traffic (say ping –google), it checks the ip routing table to see if route exists, if not it will use the default route, which is the implied router. when the implied router receives the request, it will check the vpc route table. Now the vpc route table has the rule: Destination = (all ips) ;Target: internet gateway: web-igw. So the traffic from instance is directed to internet gateway.

ping -> use implicit router: -> use  internet gateway: web-igw.

Then NAT happens (see below)

implicit routers ip -> becomes Public Elastic IP

i.e. ->

NAT Translation

AWS does network address translation (NAT). When you associate a private IP address to a Public IP Address, that enables network translation between them. The NAT translation seems to appear between the implied router and the internet gateway

# get your instances public ip
#result which is the ip of your public Elastic IP

# but if we do a ip a, notice that the public ip address is not configured. Hence AWS is doing network adress translation NAT
ip a

#if you do ifconfig the eth0 inet addr is the implicit router address :

Private VPC (shared-vpc for database)


Name: share-vpc

ipv4 cidr:


Name: database


VPC: share-vpc

Route Table

Name: shared

VPC: shared-vpc

Subnet Association

Associate database subnet with route table “shared”


EC2/Launch Instance / Community AMIs/search for: ami-1cb6b467 (same image as before, i.e. image with docker)

Network: shared-vpc

subnet: database

Network interfaces/etho/primary ip:

(note no ENI card here as this will not have a public ip as this is private)

VPC Peering & Routing

Peering is only for instance to instance connections


Name: web-shared-pcx

VPC-Requester: web-vpc

VPC-Accepter: shared-vpc

Accept Request (on Peering window)

Actions: Accept Request

Set Routes (go to route tables)

routes for route table: web-pub

Destination: (database subnet)

Target: web-shared-pcx

routes for route table: shared


Target: web-shared-pcx

Instead of creating routes to subnets in VPC, create a subnet to the VPC


Target: web-shared-pcx

ssh -i "pizza-keys.pem" ec2-user@

If Peering does not work

Peering Tutorial Quick start

  1. In the instances Security Group, add an inbound rule

    Type: ALL ICMP-PV4

    Source: Anywhere

  2. In instances Subnet, Check if route table is associated to the subnet

Secure Ingress using a NAT Instance

You can use a network address translation (NAT) instance in a public subnet in your VPC to enable instances in the private subnet to initiate outbound IPv4 traffic to the Internet or other AWS services, but prevent the instances from receiving inbound traffic initiated by someone on the Internet.

You can also use a NAT gateway (much more expensive), which is a managed NAT service that provides better availability, higher bandwidth, and requires less administrative effort. For common use cases, we recommend that you use a NAT gateway rather than a NAT instance.

We are going to give database server outbound only (egress) access to the internet

Configuring a NAT Instance

Here NAT1 instance (a linux vm) will have a route table pointing to the internet gateway (nat-pub route table)

  1. Create a gateway, name : shared-igw and attach it to vpc: “shared-vpc”

  2. Create nat-pub subnet in vnet: shared-vpc, in us-east-1a

    IPV4 Cidr:

  3. Create a Route Table:

    Name: nat-pub

    vpc: shared-vpc

  4. Add route for the internet gateway (Edit Routes)


    Target: internet gateway shared-igw

  5. Associate Subnet (Subnet Associations Tab)

    Edit subnet associations

    select nat-pub subnet

    Now you have an implied router

Configuring a NAT Instance

Amazon has provided a Linux image that is preconfigured to perform Network Address Translation

  1. Allocate a new Elastic IP

  2. Copy the PIP:

  3. Go to EC2 Instances and launch a new instance

    1. in Community AMIs, search ami-a7fdcadc
    2. Network: shared-vpc
    3. subnet: nat-pub
    4. Network interfaces/eth0/Primary IP/:
  4. Security Group: create a new security group

    1. Name: NAT Instance

    2. Rule:

      Type: SSH , Source: MyIP

      Type: ALL TCP, Source,,

      ​ description: VPC and on-prem networks

      (Note covers both and … I think; and we sonn’t have an on-premise network yes)

    3. After instance is launched, go to instance, Actions and select “Change Source/Dest. Check”

      When db1 instance gets a returns a message from the internet from the NAT, the NAT will use the source IP of the originating host from internet. The Source/Destination IPs will differ and this check will block it. Hence we must disable this check

    4. Associate Elastic IP to the nat1 instance

Configuring Routing for a NAT Client

Now we will configure the shared route table to point to the nat1 instance

Nat1 instance is associated with a public ip & can reach the internet

  1. Go to shared route table
  2. Add a route. Destination:, target: nat1 (select “instance”, then nat1). Note that target changes to eni-…

Using a Bastion Host (jump box)

You now use the nat1 instance as a jump box to configure the db1 instance

#ssh into nat1 public ip
ssh -i "pizza-keys.pem" ec2-user@

# copy key to db1 instance. First open pem file and copy in clipboard then paste on server
#ctrl-x to save

nano pizza-keys.pem

#give it restrictive permissions: remove read write; go=> group, other
chmod go-rw pizza-keys.pem

#ssh into db1
ssh -i "pizza-keys.pem" ec2-user@

To prove that db1 can access internet

#on db1 instance, which gets db1's ip, and you get back eip of nat1 instance

add WordPress on db1 (this will be our database) using docker

sudo docker run --name db1 -p 3306:3306 -d benpiper/aws-db1

add another WordPress instance on the www1 instance

ssh -i "pizza-keys.pem" ec2-user@

sudo docker run --name www1 -p 80:80 -d benpiper/aws-www1

Transit VPC

Create Transit VPC


VPC Name: transit-vpc




Subnet Name: transit

Internet Gateway

Name: transit-igw

Attach to VPC: transit-vpc

Route Table

Name: transit

VPC: Transit


* Destination:
* Target: transit_igw

Subnet Association:

​ Subnet: transit