AWS Site-to-Site VPN and AWS Client VPN

AWS VPN is comprised of two services: 

  • AWS Site-to-Site VPN enables you to securely connect your on-premises network to Amazon VPC, for example your branch office site. 
  • AWS Client VPN enables you to securely connect users to AWS or on-premises networks, for example remote employees. 

AWS Site-to-Site VPN

ased on IPsec technology, AWS Site-to-Site VPN uses a VPN tunnel to pass data from the customer network to or from AWS.

One AWS Site-to-Site VPN connection consists of two tunnels. Each tunnel terminates in a different Availability Zone on the AWS side, but it must terminate on the same customer gateway on the customer side. 

AWS Site-to-Site VPN components

Customer gateway

A resource you create and configure in AWS that represents your on-premise gateway device. The resource contains information about the type of routing used by the Site-to-Site VPN, BGP, ASN and other optional configuration information.

Customer gateway device

A customer gateway device is a physical device or software application on your side of the AWS Site-to-Site VPN connection. 

Virtual private gateway

A virtual private gateway is the VPN concentrator on the Amazon side of the AWS Site-to-Site VPN connection. You use a virtual private gateway or a transit gateway as the gateway for the Amazon side of the AWS Site-to-Site VPN connection.

Transit gateway

A transit gateway is a transit hub that can be used to interconnect your VPCs and on-premises networks. You use a transit gateway or virtual private gateway as the gateway for the Amazon side of the AWS Site-to-Site VPN connection.

AWS Site-to-Site VPN limitations

  • IPv6 traffic is partially supported. AWS Site-to-Site VPN supports IPv4/IPv6-Dualstack through separate tunnels for inner traffic. IPv6 for outer tunnel connection not supported.
  • AWS Site-to-Site VPN does not support Path MTU Discovery. The greatest Maximum Transmission Unit (MTU) available on the inside tunnel interface is 1,399 bytes.
  • Throughput of AWS Site-to-Site VPN connections is limited. When terminating on a virtual private gateway, only one tunnel out of the pair can be active and carry a maximum of 1.25 Gbps. However, real-life throughput will be about 1 Gbps. When terminating on AWS Transit Gateway, both tunnels in the pair can be active and carry an aggregate maximum of 2.5 Gbps. However, real-life throughput will be 2 Gbps. Each flow (for example, TCP stream) will still be limited to a maximum of 1.25 Gbps, with a real-life value of about 1 Gbps.
  • Maximum packets per second (PPS) per VPN tunnel is 140,000.
  • AWS Site-to-Site VPN terminating on AWS Transit Gateway supports equal-cost multi-path routing (ECMP) and multi-exit discriminator (MED) across tunnels in the same and different connection. ECMP is only supported for Site-to-Site VPN connections activated on an AWS Transit Gateway. MED is used to identify the primary tunnel for Site-to-Site VPN conncetions that use BGP. Note, BFD is not yet supported on AWS Site-to-Site VPN, though it is supported on Direct Connect. 
  • AWS Site-to-Site VPN endpoints use public IPv4 addresses and therefore require a public virtual interface to transport traffic over Direct Connect. Support for AWS Site-to-Site VPN over private Direct Connect is not yet available. 
  • For globally distributed applications, the accelerated Site-to-Site VPN option provides a connection to the global AWS backbone through AWS Global Accelerator. Because the Global Accelerator IP space is not announced over a Direct Connect public virtual interface, you cannot use accelerated Site-to-Site VPN with a Direct Connect public virtual interface.

In addition, when you connect your VPCs to a common on-premises network, it’s recommend that you use nonoverlapping CIDR blocks for your networks. 

Client VPN

Based on OpenVPN technology, Client VPN is a managed client-based VPN service that lets you securely access your AWS resources and resources in your on-premises network. With Client VPN, you can access your resources from any location using an OpenVPN-based VPN client. 

Client VPN components

Client VPN endpoint

Your Client VPN administrator creates and configures a Client VPN endpoint in AWS. Your administrator controls which networks and resources you can access when you establish a VPN connection. 

VPN client application

This is the software application that you use to connect to the Client VPN endpoint and establish a secure VPN connection.

Client VPN endpoint configuration file

This is a configuration file that is provided to you by your Client VPN administrator. The file includes information about the Client VPN endpoint and the certificates required to establish a VPN connection. You load this file into your chosen VPN client application. 

Client VPN limitations

  • Client VPN supports IPv4 traffic only. IPv6 is not supported.
  • Security Assertion Markup Language (SAML) 2.0-based federated authentication only works with an AWS provided client v1.2.0 or later. 
  • SAML integration with AWS Single Sign-On requires a workaround. Better integration is being worked on. 
  • Client CIDR ranges must have a block size of at least /22 and must not be greater than /12. 
  • A Client VPN endpoint does not support subnet associations in a dedicated tenancy VPC. 
  • Client VPN is not compliant with Federal Information Processing Standards (FIPS).
  • Client CIDR ranges cannot overlap with the local CIDR of the VPC in which the associated subnet is located. It also cannot overlap any routes manually added to the Client VPN endpoint’s route table.
  • A portion of the addresses in the client CIDR range is used to support the availability model of the Client VPN endpoint and cannot be assigned to clients. Therefore, we recommend that you assign a CIDR block that contains twice the number of required IP addresses. This will ensure the maximum number of concurrent connections that you plan to support on the Client VPN endpoint. 
  • The client CIDR range cannot be changed after you create the Client VPN endpoint. 
  • The subnets associated with a Client VPN endpoint must be in the same VPC.
  • You cannot associate multiple subnets from the same Availability Zone with a Client VPN endpoint. 
  • AWS Certificate Manager (ACM) certificates are not supported with mutual authentication because you cannot extract the private key. You can use an ACM server as the server-side certificate. But, to add a client certificate to your customer configuration, you cannot use a general ACM certificate because you can’t extract the required private key details. So you must access the keys in one of two ways. Either generate your own certificate where you have the key or use AWS Certificate Manager Private Certificate Authority (ACM PCA), which gives the private keys. If the customer is authenticating based on Active Directory or SAML, they can use a general ACM-generated certificate because only the server certificate is required.

Cheers
Osama

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