AWS VPC VPN – CloudHub Connections – Certification

VPC VPN Connections

  • VPC VPN connections are used to extend on-premise data centers to AWS
  • VPC VPN connections provide secure IPSec connections from on-premise computers/services to AWS
  • AWS hardware VPN
    • Connectivity can be established by creating an IPSec, hardware VPN connection between the VPC and the remote network.
    • On the AWS side of the VPN connection, a Virtual Private Gateway (VGW) provides two VPN endpoints for automatic failover.
    • On customer side a customer gateway (CGW) needs to be configured, which is the physical device or software application on the remote side of the VPN connection
  • AWS Direct Connect
    • AWS Direct Connect provides a dedicated private connection from a remote network to your VPC.
    • Direct Connect can be combined with an AWS hardware VPN connection to create an IPsec-encrypted connection
  • AWS VPN CloudHub
    • For more than one remote network for e.g. multiple branch offices, multiple AWS hardware VPN connections can be created via the VPC to enable communication between these networks
  • Software VPN
    • VPN connection can be setup by running a software VPN like OpenVPN appliance on an EC2 instance in the VPC
    • AWS does not provide or maintain software VPN appliances; however, there are range of products provided by partners and open source communities

Hardware VPN Connection

VPN ConnectionVPN Components

  • Virtual Private Gateway – VGW
    • A virtual private gateway is the VPN concentrator on the AWS side of the VPN connection
  • Customer Gateway – CGW
    • A customer gateway is a physical device or software application on customer side of the VPN connection.
    • When a VPN connection is created, the VPN tunnel comes up when traffic is generated from the remote side of the VPN connection.
    • VGW is not the initiator; CGW must initiate the tunnels
    • If the VPN connection experiences a period of idle time, usually 10  seconds, depending on the configuration, the tunnel may go down. To prevent this, a network monitoring tool to generate keepalive pings; for e.g. by using IP SLA.

VPN Configuration

  • VPC has an attached virtual private gateway, and the remote network includes a customer gateway, which must be configured to enable the
    VPN connection.
  • Routing must be setup so that any traffic from the VPC bound for the remote network is routed to the virtual private gateway.
  • Each VPN has two tunnels associated with it that can be configured on the customer router, as is not single point of failure
  • Multiple VPN connections to a single VPC can be created, and a second CGW can be configured to create a redundant connection to the same external location or to create VPN connections to multiple geographic locations.

VPN Routing Options

  • For a VPN connection, the route table for the subnets should be updated with the type of routing (static of dynamic) that you plan to use.
  • Route tables determine where network traffic is directed. Traffic destined for the VPN connections must be routed to the virtual private gateway.
  • Type of routing can depend on the make and model of your VPN devices.
    • Static Routing
      • If your device does not support BGP, specify static routing.
      • Using static routing, the routes (IP prefixes) can be specified that should be communicated to the virtual private gateway.
      • Devices that don’t support BGP may also perform health checks to assist failover to the second tunnel when needed.
    • BGP dynamic routing
      • If the VPN device supports Border Gateway Protocol (BGP), specify dynamic routing with the VPN connection.
      • When using a BGP device, static routes need not be specified to the VPN connection because the device uses BGP for auto discovery and to advertise its routes to the virtual private gateway.
      • BGP-capable devices are recommended as the BGP protocol offers robust liveness detection checks that can assist failover to the second VPN tunnel if the first tunnel goes down.
  • Only IP prefixes known to the virtual private gateway, either through BGP advertisement or static route entry, can receive traffic from your VPC.
  • Virtual private gateway does not route any other traffic destined outside of the advertised BGP, static route entries, or its attached VPC CIDR.

VPN Connection Redundancy

VPN Connection Redundancy

  • A VPN connection is used to connect the customer network to a VPC.
  • Each VPN connection has two tunnels to help ensure connectivity in case one of the VPN connections becomes unavailable, with each tunnel using a unique virtual private gateway public IP address.
  • Both tunnels should be configured for redundancy.
  • When one tunnel becomes unavailable, for e.g. down for maintenance, network traffic is automatically routed to the available tunnel for that specific VPN connection.
  • To protect against a loss of connectivity in case the customer gateway becomes unavailable, a second VPN connection can be setup to the VPC and virtual private gateway by using a second customer gateway.
  • Customer gateway IP address for the second VPN connection must be publicly accessible.
  • By using redundant VPN connections and CGWs, maintenance on one of the customer gateways can be performed while traffic continues to flow over the second customer gateway’s VPN connection.
  • Dynamically routed VPN connections using the Border Gateway Protocol (BGP) are recommended, if available, to exchange routing information between the customer gateways and the virtual private gateways.
  • Statically routed VPN connections require static routes for the network to be entered on the customer gateway side.
  • BGP-advertised and statically entered route information allow gateways on both sides to determine which tunnels are available and reroute traffic if a failure occurs.

VPN CloudHub

  • VPN CloudHub can be used to provide secure communication between sites, if you have multiple VPN connections
  • VPN CloudHub operates on a simple hub-and-spoke model that can be used with or without a VPC.
  • Design is suitable for customers with multiple branch offices and existing
    Internet connections who’d like to implement a convenient, potentially low-cost hub-and-spoke model for primary or backup connectivity between these remote offices

VPN CloudHub Architecture

  • VPN CloudHub architecture with blue dashed lines indicates network
    traffic between remote sites being routed over their VPN connections.
  • AWS VPN CloudHub requires a virtual private gateway with multiple customer gateways.
  • Each customer gateway can either have a unique or same Border Gateway Protocol (BGP) Autonomous System Number (ASN)
  • Customer gateways advertise the appropriate routes (BGP prefixes) over their VPN connections.
  • Routing advertisements are received and re-advertised to each BGP peer, enabling each site to send data to and receive data from the other sites.
  • Routes for each spoke must have unique ASNs and the sites must not have overlapping IP ranges.
  • Each site can also send and receive data from the VPC as if they were using a standard VPN connection.
  • Sites that use AWS Direct Connect connections to the virtual private gateway can also be part of the AWS VPN CloudHub.
  • To configure the AWS VPN CloudHub,
    • multiple customer gateways can be created, each with the unique public IP address of the gateway and the ASN.
    • a VPN connection can be created from each customer gateway to a common virtual private gateway.
    • each VPN connection must advertise its specific BGP routes. This is done using the network statements in the VPN configuration files for the VPN connection.

AWS Certification Exam Practice Questions

  • Questions are collected from Internet and the answers are marked as per my knowledge and understanding (which might differ with yours).
  • AWS services are updated everyday and both the answers and questions might be outdated soon, so research accordingly.
  • AWS exam questions are not updated to keep up the pace with AWS updates, so even if the underlying feature has changed the question might not be updated
  • Open to further feedback, discussion and correction.
  1. You have in total 5 offices, and the entire employee related information is stored under AWS VPC instances. Now all the offices want to connect the instances in VPC using VPN. Which of the below help you to implement this?
    1. you can have redundant customer gateways between your data center and your VPC
    2. you can have multiple locations connected to the AWS VPN CloudHub
    3. You have to define 5 different static IP addresses in route table.
    4. 1 and 2
    5. 1,2 and 3
  2. You have in total 15 offices, and the entire employee related information is stored under AWS VPC instances. Now all the offices want to connect the instances in VPC using VPN. What problem do you see in this scenario?
    1. You can not create more than 1 VPN connections with single VPC (Can be created)
    2. You can not create more than 10 VPN connections with single VPC (soft limit can be extended)
    3. When you create multiple VPN connections, the virtual private gateway can not sends network traffic to the appropriate VPN connection using statically assigned routes. (Can route the traffic to correct connection)
    4. Statically assigned routes cannot be configured in case of more than 1 VPN with virtual private gateway. (can be configured)
    5. None of above
  3. You have been asked to virtually extend two existing data centers into AWS to support a highly available application that depends on existing, on-premises resources located in multiple data centers and static content that is served from an Amazon Simple Storage Service (S3) bucket. Your design currently includes a dual-tunnel VPN connection between your CGW and VGW. Which component of your architecture represents a potential single point of failure that you should consider changing to make the solution more highly available?
    1. Add another VGW in a different Availability Zone and create another dual-tunnel VPN connection.
    2. Add another CGW in a different data center and create another dual-tunnel VPN connection. (Refer link)
    3. Add a second VGW in a different Availability Zone, and a CGW in a different data center, and create another dual-tunnel.
    4. No changes are necessary: the network architecture is currently highly available.
  4. You are designing network connectivity for your fat client application. The application is designed for business travelers who must be able to connect to it from their hotel rooms, cafes, public Wi-Fi hotspots, and elsewhere on the Internet. You do not want to publish the application on the Internet. Which network design meets the above requirements while minimizing deployment and operational costs? [PROFESSIONAL]
    1. Implement AWS Direct Connect, and create a private interface to your VPC. Create a public subnet and place your application servers in it. (High Cost and does not minimize deployment)
    2. Implement Elastic Load Balancing with an SSL listener that terminates the back-end connection to the application. (Needs to be published to internet)
    3. Configure an IPsec VPN connection, and provide the users with the configuration details. Create a public subnet in your VPC, and place your application servers in it. (Instances still in public subnet are internet accessible)
    4. Configure an SSL VPN solution in a public subnet of your VPC, then install and configure SSL VPN client software on all user computers. Create a private subnet in your VPC and place your application servers in it. (Cost effective and can be in private subnet as well)
  5. You are designing a connectivity solution between on-premises infrastructure and Amazon VPC Your server’s on-premises will De communicating with your VPC instances You will De establishing IPSec tunnels over the internet You will be using VPN gateways and terminating the IPsec tunnels on AWS-supported customer gateways. Which of the following objectives would you achieve by implementing an IPSec tunnel as outlined above? (Choose 4 answers) [PROFESSIONAL]
    1. End-to-end protection of data in transit
    2. End-to-end Identity authentication
    3. Data encryption across the Internet
    4. Protection of data in transit over the Internet
    5. Peer identity authentication between VPN gateway and customer gateway
    6. Data integrity protection across the Internet


AWS VPC NAT – NAT Gateway – Certification

NAT Overview

  • Network Address Translation (NAT) devices, launched in the public subnet, enables instances in a private subnet to connect to the Internet, but prevents the Internet from initiating connections with the instances.
  • Instances in private subnets would need internet connection for performing software updates or trying to access external services
  • NAT device performs the function of both address translation and port address translation (PAT)
  • NAT instance prevents instances to be directly exposed to the Internet and having to be launched in Public subnet and assignment of the Elastic IP address to all, which are limited.
  • NAT device routes the traffic, from the private subnet to the Internet, by replacing the source IP address with its address and for the response traffic it translates the address back to the instances’ private IP addresses.
  • AWS allows NAT configuration in 2 ways
    • NAT Instance
    • NAT Gateway, managed service by AWS

NAT device Configuration Key Points

  • needs to be launched in the Public Subnet
  • needs to be associated with an Elastic IP address (or public IP address)
  • should have the Source/Destination flag disabled to route traffic from the instances in the private subnet to the Internet and send the response back
  • should have a Security group associated that
    • allows Outbound Internet traffic from instances in the private subnet
    • disallows Inbound Internet traffic from everywhere
  • Instances in the private subnet should have the Route table configured to direct all Internet traffic to the NAT device

NAT Gateway

NAT gateway is a AWS managed NAT service that provides better availability, higher bandwidth, and requires less administrative effort.

  • A NAT gateway supports bursts of up to 10 Gbps of bandwidth.
  • For more than 10 Gbps bursts requirement, the workload can be distributed by splitting the resources into multiple subnets, and creating a NAT gateway in each subnet.
  • NAT gateway is associated with One Elastic IP address which cannot be disassociated after it’s creation.
  • Each NAT gateway is created in a specific Availability Zone and implemented with redundancy in that zone.
  • A NAT gateway supports the following protocols: TCP, UDP, and ICMP.
  • NAT gateway cannot be associated a security group. Security can be configured for the instances in the private subnets to control the traffic
  • Network ACL can be used to control the traffic to and from the subnet. Network ACL applies to the NAT gateway’s traffic, which uses ports 1024 – 65535.
  • NAT gateway when created receives an elastic network interface that’s automatically assigned a private IP address from the IP address range of your subnet. Attributes of this network interface cannot be modified
  • NAT gateway cannot send traffic over VPC endpoints, VPN connections, AWS Direct Connect, or VPC peering connections. Private subnet’s route table should be modified to route the traffic directly to these devices.

NAT Instance

  • NAT instance can be created by using Amazon Linux AMIs configured to route traffic to Internet.
  • They do not provide the same availability and bandwidth and need to configured as per the application needs.
  • NAT instances must have security groups associated with Inbound traffic enabled from private subnets and Outbound traffic enabled to the Internet
  • NAT instances should have the Source Destination Check attribute disabled, as it is neither the source nor the destination for the traffic and merely acts as a gateway

High Availability NAT Instance

NAT Instance High Availability

  • Create One NAT instance per Availability Zone
  • Configure all Private subnet route tables to the same zone NAT instance
  • User Auto Scaling for NAT availability
  • User Auto Scaling group per NAT instance with min and max size set of 1. So if NAT instances fail, Auto Scaling will automatically launch an replacement instance
  • NAT instance is highly available with limited downtime
  • Let Auto Scaling monitor health and availability of the NAT instance
  • Bootstrap scripts with the NAT instance to update the Route tables programmatically
  • Keep a close watch on the Network Metrics and scale vertically the NAT instance type to the one with high network performance

Disabling Source/Destination checks

  • Each EC2 instance performs source/destination checks, by default, and the instance must be the source or destination of any traffic it sends or receives.
  • However, as the NAT instance acts as a router between the Internet and the instances in the private subnet it must be able to send and receive traffic when the source or destination is not itself.
  • Therefore, the source/destination checks on the NAT instance should be disabled

NAT Gateway & Instance Comparison

NAT Gateway vs NAT Instance

AWS Certification Exam Practice Questions

  • Questions are collected from Internet and the answers are marked as per my knowledge and understanding (which might differ with yours).
  • AWS services are updated everyday and both the answers and questions might be outdated soon, so research accordingly.
  • AWS exam questions are not updated to keep up the pace with AWS updates, so even if the underlying feature has changed the question might not be updated
  • Open to further feedback, discussion and correction.
  1. After launching an instance that you intend to serve as a NAT (Network Address Translation) device in a public subnet you modify your route tables to have the NAT device be the target of internet bound traffic of your private subnet. When you try and make an outbound connection to the Internet from an instance in the private subnet, you are not successful. Which of the following steps could resolve the issue?
    1. Attaching a second Elastic Network interface (ENI) to the NAT instance, and placing it in the private subnet
    2. Attaching an Elastic IP address to the instance in the private subnet
    3. Attaching a second Elastic Network Interface (ENI) to the instance in the private subnet, and placing it in the public subnet
    4. Disabling the Source/Destination Check attribute on the NAT instance
  2. You manually launch a NAT AMI in a public subnet. The network is properly configured. Security groups and network access control lists are property configured. Instances in a private subnet can access the NAT. The NAT can access the Internet. However, private instances cannot access the Internet. What additional step is required to allow access from the private instances?
    1. Enable Source/Destination Check on the private Instances.
    2. Enable Source/Destination Check on the NAT instance.
    3. Disable Source/Destination Check on the private instances
    4. Disable Source/Destination Check on the NAT instance
  3. A user has created a VPC with public and private subnets. The VPC has CIDR The private subnet uses CIDR and the public subnet uses CIDR The user is planning to host a web server in the public subnet (port 80. and a DB server in the private subnet (port 3306.. The user is configuring a security group of the NAT instance. Which of the below mentioned entries is not required for the NAT security group?
    1. For Inbound allow Source: on port 80
    2. For Outbound allow Destination: on port 80
    3. For Inbound allow Source: on port 80 (Refer NATSG)
    4. For Outbound allow Destination: on port 443
  4. A web company is looking to implement an external payment service into their highly available application deployed in a VPC. Their application EC2 instances are behind a public facing ELB. Auto scaling is used to add additional instances as traffic increases. Under normal load the application runs 2 instances in the Auto Scaling group but at peak it can scale 3x in size. The application instances need to communicate with the payment service over the Internet, which requires whitelisting of all public IP addresses used to communicate with it. A maximum of 4 whitelisting IP addresses are allowed at a time and can be added through an API. How should they architect their solution?
    1. Route payment requests through two NAT instances setup for High Availability and whitelist the Elastic IP addresses attached to the NAT instances
    2. Whitelist the VPC Internet Gateway Public IP and route payment requests through the Internet Gateway. (Internet gateway is only to route traffic)
    3. Whitelist the ELB IP addresses and route payment requests from the Application servers through the ELB. (ELB does not have a fixed IP address)
    4. Automatically assign public IP addresses to the application instances in the Auto Scaling group and run a script on boot that adds each instances public IP address to the payment validation whitelist API. (would exceed the allowed 4 IP addresses)