Always On VPN Load Balancing with Loadbalancer.org

Recently, I had the opportunity to deploy the Loadbalancer.org load balancer as part of an enterprise Always On VPN deployment. In the past, I’ve published guidance for using F5 BIG-IP, Citrix ADC (formerly NetScaler), and Kemp LoadMaster, so in this post, I’ll provide guidance for configuring Loadbalancer.org for Always On VPN.

IKEv2

Open the Loadbalancer.org management console and follow the steps below to configure Always On VPN load balancing on the appliance.

Create Virtual Service

Create a layer 4 virtual service for IKEv2.

  1. Click Cluster Configuration.
  2. Click Layer 4 – Virtual Services.
  3. Click Add a new Virtual Service.
  4. Enter a descriptive name for the virtual service in the Label field.
  5. Enter the virtual IP address (VIP) for the service in the IP Address field.
  6. Enter 500,4500 in the Ports field.
  7. Select UDP from the Protocol drop-down list.
  8. Select NAT from the Forwarding Method drop-down list.
  9. Click Update.

Add Real Servers

Add real servers to the virtual service.

  1. Click Layer 4 – Real Servers.
  2. Click Add a new Real Server next to the IKEv2 virtual service.
  3. Enter a descriptive name for the real server in the Label field.
  4. Enter the IP address of the real server in the Real Server IP Address field.
  5. Click Update.
  6. Repeat these steps for each additional VPN server in the cluster.

SSTP

Follow the steps below to configure SSTP load balancing on the appliance.

Create Virtual Service

Create a layer 4 virtual service for SSTP.

  1. Click Cluster Configuration.
  2. Click Layer 4 – Virtual Services.
  3. Click Add a new Virtual Service.
  4. Enter a descriptive name for the virtual service in the Label field.
  5. Enter the virtual IP address (VIP) for the service in the IP Address field.
  6. Enter 443 in the Ports field.
  7. Select TCP from the Protocol drop-down list.
  8. Select NAT from the Forwarding Method drop-down list.
  9. Click Update.

Configure Virtual Service Health Check

Update the health check method for the SSTP virtual service.

  1. Click Layer 4 – Virtual Services.
  2. Click Modify on the SSTP virtual service.
  3. Select Negotiate from the Check Type drop-down list in the Health Checks section.
  4. Enter 443 in the Check Port field.
  5. Select HTTPS from the Protocol drop-down list.
  6. Enter /sra_{BA195980-CD49-458b-9E23-C84EE0ADCD75}/ in the Request to send field.
  7. Enter 401 in the Response expected field.
  8. Click Update.

Note: Using the Negotiate health check type for the SSTP monitor on Loadbalancer.org appliances requires version 8.13.0 or later. Administrators can use the External script option when using earlier releases of Loadbalancer.org appliances. An SSTP health check script for Loadbalancer.org can be found here.

Add Real Servers

Add real servers to the virtual service.

  1. Click Layer 4 – Real Servers.
  2. Click Add a new Real Server next to the SSTP virtual service.
  3. Enter a descriptive name for the real server in the Label field.
  4. Enter the IP address of the real server in the Real Server IP Address field.
  5. Click Update.
  6. Repeat these steps for each additional VPN server in the cluster.

Review

Once complete, click System Overview to view the overall health of your VPN servers.

Summary

The Loadbalancer.org appliance is an efficient, cost-effective, and easy-to-configure load-balancing solution that works well with Always On VPN implementations. It’s available as a physical or virtual appliance. There’s also a cloud-based version. It also includes advanced features such as TLS offload, web application firewall (WAF), global server load balancing (GSLB), and more. If you are looking for a layer 4-7 load balancer for Always On VPN and other workloads, be sure to check them out.

Additional Information

Loadbalancer.org Virtual Appliance

SSTP Health Check Script for Loadbalancer.org

Always On VPN Client IP Address Assignment Methods

When Always On VPN clients connect to the VPN server, they must be assigned an IP address to facilitate network communication. When using Windows Server and Routing and Remote Access Service (RRAS) for VPN services, administrators must choose between Dynamic Host Configuration Protocol (DHCP) and static address pool assignment methods.

DHCP

DHCP is a quick and easy way to handle VPN client IP address assignment. However, there are some drawbacks and limitations associated with this option. Consider the following.

Allocation

DHCP for Always On VPN clients does not work as you might expect. For example, when a VPN client connects, it does not obtain its IP address directly from the DHCP server. Instead, the VPN server leases a block of IP addresses from the DHCP server and manages those on behalf of its clients. On the DHCP server, you will see the Unique ID column of these IP address leases indicating RAS.

Address Block Size

After configuring the VPN server to use DHCP VPN client IP address assignment, the VPN server will automatically lease a block of ten IP addresses from a DHCP server. When this initial block of ten IP addresses is exhausted, the VPN server will lease another block of ten IP addresses. Administrators can increase the size of the requested address block by creating the following registry key on each VPN server.

Key: HKLM\SYSTEM\CurrentControlSet\Services\RemoteAccess\Parameters\IP
Value: InitialAddressPoolSize
Type: DWORD
Data: <size of DHCP pool request>

Alternatively, administrators can download Update-VpnServerDhcpPoolSize.ps1 from my GitHub repository and run it on each VPN server to increase the size of the initial DHCP address pool request.

DHCP Options

The VPN server discards all DHCP option information returned by the DHCP server. The VPN server uses only the IP address from the DHCP lease. The client is unaware of any other information in the DHCP lease.

Subnet

By default, the VPN server will only request DHCP addresses from a scope that matches the same subnet as the IP address assigned to the VPN server’s network adapter. If the VPN server has more than one network interface, it will send DHCP requests from the network interface listed on the Adapter drop-down list, as shown here.

Note: This option is only available on servers configured with multiple network interfaces. Also, if the value is set to Allow RAS to select adapter, it is best to specifically define the network interface where DHCP and DNS requests are made.

Scope Size

When using the DHCP assignment method, ensure the DHCP scope contains enough IP addresses to support the number of concurrent connections expected on all VPN servers.

IPv6

DHCPv6 is not supported on RRAS for VPN client IP address assignment. The only option for IPv6 is prefix assignment.

RRAS in Azure

DHCP is not supported when deploying RRAS in Azure. Administrators deploying RRAS in Azure to support Always On VPN must use the static address pool assignment method. More details here.

Known Issues

When using DHCP with Windows Server 2019 RRAS servers, a known issue prevents this from working correctly. Administrators can download Update-VpnServerDhcpPrivileges.ps1 from my GitHub repository and run it on each VPN server to ensure proper DHCP operation.

Increased Complexity

Since the VPN server leases IP addresses on behalf of clients and discards DHCP option information included in the lease, there’s no real benefit to using DHCP. Using DHCP only adds complexity and introduces another dependency, making the solution more brittle and difficult to manage. Using the static address pool assignment method is a better choice.

Static Pool

Implementation best practices dictate using the static address pool assignment method instead of DHCP. The following is guidance for configuring RRAS to support the static address pool option for VPN client IP address assignment.

Unique Subnet

Using a unique IP subnet is best when using the static address pool assignment method. However, this also requires configuring internal network routing to return traffic for that subnet to the individual VPN server where that subnet is assigned. Each server must have a unique IP address pool assigned. Define static address pools using subnet boundaries when configuring multiple VPN servers. Assigning IP address pools along subnet boundaries simplifies internal network routing configuration. Ensure that assigned IP address pool subnets are large enough to accommodate the total number of concurrent connections expected on each server. Be sure to overprovision to handle failover scenarios.

Same Subnet

Alternatively, administrators can assign VPN client IP addresses from the same subnet as the VPN server’s network interface. Assigning VPN client IP addresses from the same subnet as the VPN server eliminates the need for any internal network routing configuration, simplifying deployment. However, server subnets are often small and may not have enough IP address space to support numerous concurrent VPN connections. Be sure to plan accordingly.

Static IP Addresses

It is possible to assign a static IP address to an individual user. However, assigning a static IP address to a specific device is not. I will discuss static IP address assignments for Always On VPN clients in a future blog post.

Other Limitations

Here are some additional things to consider when creating a VPN client IP addressing strategy.

DNS

Always On VPN clients can be configured to register their IP address in DNS. However, the VPN client configuration controls this setting. The DHCP server does not register IP addresses in DNS when using DHCP. The client registers its IP address in DNS directly after it connects. In addition, a VPN client will receive a different IP address each time it connects to the VPN server. DNS propagation can delay hostname resolution on-premises for remote-connected VPN clients.

Selective Addressing

Regardless of which assignment method is selected, assigning different IP addresses to different types of connections is not possible. For example, a common ask is to assign user connections from one IP address pool and device connections from another. The only option to support this is to use different servers for each type of connection.

Summary

The best practice for IPv4 VPN client addressing is to use the static address pool method with a unique IPv4 subnet per server. Using static address pool assignment provides the most flexible configuration options and eliminates the dependency on internal services, making the solution more resilient and easier to manage. A unique address pool per server ensures that a large enough subnet can be defined to support the expected number of concurrent connections, regardless of the subnet size the VPN server is assigned to. Also, a unique IP subnet for VPN clients makes configuring internal firewall rules to control VPN client access easier.

Additional Information

Always On VPN and IPv6

Always On VPN Client DNS Server Configuration

Always On VPN Routing Configuration

Always On VPN RRAS Internal Interface Non-Operational

Deployment Considerations for DirectAccess on Amazon Web Services (AWS)

Organizations are rapidly deploying Windows server infrastructure with public cloud providers such as Amazon Web Services (AWS) and Microsoft Azure. With traditional on-premises infrastructure now hosted in the cloud, DirectAccess is also being deployed there more commonly.

Supportability

Interestingly, Microsoft has expressly stated that DirectAccess is not formally supported on their own public cloud platform, Azure. However, there is no formal statement of non-support for DirectAccess hosted on other non-Microsoft public cloud platforms. With supportability for DirectAccess on AWS unclear, many companies are taking the approach that if it isn’t unsupported, then it must be supported. I’d suggest proceeding with caution, as Microsoft could issue formal guidance to the contrary in the future.

DirectAccess on AWS

Deploying DirectAccess on AWS is similar to deploying on premises, with a few notable exceptions, outlined below.

IP Addressing

It is recommended that an IP address be exclusively assigned to the DirectAccess server in AWS, as shown here.

Deployment Considerations for DirectAccess on Amazon Web Services (AWS)

Prerequisites Check

When first configuring DirectAccess, the administrator will encounter the following warning message.

“The server does not comply with some DirectAccess prerequisites. Resolve all issues before proceed with DirectAccess deployment.”

The warning message itself states that “One or more network adapters should be configured with a static IP address. Obtain a static address and assign it to the adapter.

Deployment Considerations for DirectAccess on Amazon Web Services (AWS)

IP addressing for virtual machines are managed entirely by AWS. This means the DirectAccess server will have a DHCP-assigned address, even when an IP address is specified in AWS. Assigning static IP addresses in the guest virtual machine itself is also not supported. However, this warning message can safely be ignored.

No Support for Load Balancing

It is not possible to create load-balanced clusters of DirectAccess servers for redundancy or scalability on AWS. This is because enabling load balancing for DirectAccess requires the IP address of the DirectAccess server be changed in the operating system, which is not supported on AWS. To eliminate single points of failure in the DirectAccess architecture or to add additional capacity, multisite must be enabled. Each additional DirectAccess server must be provisioned as an individual entry point.

Network Topology

DirectAccess servers on AWS can be provisioned with one or two network interfaces. Using two network interfaces is recommended, with the external network interface of the DirectAccess server residing in a dedicated perimeter/DMZ network. The external network interface must use either the Public or Private Windows firewall profile. DirectAccess will not work if the external interface uses the Domain profile. For the Public and Private profile to be enabled, domain controllers must not be reachable from the perimeter/DMZ network. Ensure the perimeter/DMZ network cannot access the internal network by restricting network access in EC2 using a Security Group, or on the VPC using a Network Access Control List (ACL) or custom route table settings.

External Connectivity

A public IPv4 address must be associated with the DirectAccess server in AWS. There are several ways to accomplish this. The simplest way is to assign a public IPv4 address to the virtual machine (VM). However, a public IP address can only be assigned to the VM when it is deployed initially and cannot be added later. Alternatively, an Elastic IP can be provisioned and assigned to the DirectAccess server at any time.

An ACL must also be configured for the public IP that restricts access from the Internet to only inbound TCP port 443. To provide additional protection, consider deploying an Application Delivery Controller (ADC) appliance like the Citrix NetScaler or F5 BIG-IP to enforce client certificate authentication for DirectAccess clients.

Network Location Server (NLS)

If an organization is hosting all of its Windows infrastructure in AWS and all clients will be remote, Network Location Server (NLS) availability becomes much less critical than with traditional on-premises deployments. For cloud-only deployments, hosting the NLS on the DirectAccess server is a viable option. It eliminates the need for dedicated NLS, reducing costs and administrative overhead. If multisite is configured, ensure that the NLS is not using a self-signed certificate, as this is unsupported.

Deployment Considerations for DirectAccess on Amazon Web Services (AWS)

However, for hybrid cloud deployments where on-premises DirectAccess clients share the same internal network with cloud-hosted DirectAccess servers, it is recommended that the NLS be deployed on dedicated, highly available servers following the guidance outlined here and here.

Client Provisioning

All supported DirectAccess clients will work with DirectAccess on AWS. If the domain infrastructure is hosted exclusively in AWS, provisioning clients can be performed using Offline Domain Join (ODJ). Provisioning DirectAccess clients using ODJ is only supported in Windows 8.x/10. Windows 7 clients cannot be provisioned using ODJ and must be joined to the domain using another form of remote network connectivity such as VPN.

Additional Resources

DirectAccess No Longer Supported in Microsoft Azure

Microsoft Server Software Support for Azure Virtual Machines

DirectAccess Network Location Server (NLS) Guidance

DirectAccess Network Location Server (NLS) Deployment Considerations for Large Enterprises

Provisioning DirectAccess Clients using Offline Domain Join (ODJ)

DirectAccess SSL Offload and IP-HTTPS Preauthentication with Citrix NetScaler

DirectAccess SSL Offload and IP-HTTPS Preauthentication with F5 BIG-IP

Planning and Implementing DirectAccess with Windows Server 2016 Video Training Course

Implementing DirectAccess with Windows Server 2016 Book