Always On VPN IKEv2 Load Balancing with KEMP LoadMaster

Always On VPN IKEv2 Load Balancing with KEMP LoadMasterInternet Key Exchange version 2 (IKEv2) is an IPsec-based VPN protocol with configurable security parameters that allows administrators to ensure the highest level of security for Windows 10 Always On VPN clients. It is the protocol of choice for deployments that require the best possible protection for communication between remote clients and the VPN server. IKEv2 has some unique requirements when it comes to load balancing, however. Because it uses UDP on multiple ports, configuring the load balancer requires some additional steps for proper operation. This article demonstrates how to enable IKEv2 load balancing using the Kemp LoadMaster load balancer.

IKEv2 and NAT

IKEv2 VPN security associations (SAs) begin with a connection to the VPN server that uses UDP port 500. During this initial exchange, if it is determined that the client, server, or both are behind a device performing Network Address Translation (NAT), the connection switches to UDP port 4500 and the connection establishment process continues.

IKEv2 Load Balancing Challenges

Since UDP is connectionless, there’s no guarantee that when the conversation switches from UDP 500 to UDP 4500 that the load balancer will forward the request to the same VPN server on the back end. If the load balancer forwards the UDP 500 session from a VPN client to one real server, then forwards the UDP 4500 session to a different VPN server, the connection will fail. The load balancer must be configured to ensure that both UDP 500 and 4500 from the same VPN client are always forwarded to the same real server to ensure proper operation.

Port Following

To meet this unique requirement for IKEv2 load balancing, it is necessary to use a feature on the KEMP LoadMaster load balancer called “port following”. Enabling this feature will ensure that a VPN client using IKEv2 will always have their UDP 500 and 4500 sessions forwarded to the same real server.

Load Balancing IKEv2

Open the web-based management console and perform the following steps to enable load balancing of IKEv2 traffic on the KEMP LoadMaster load balancer.

Create the Virtual Server

  1. Expand Virtual Services.
  2. Click Add New.
  3. Enter the IP address to be used by the virtual server in the Virtual Address field.
  4. Enter 500 in the Port field.
  5. Select UDP from the Protocol drop-down list.
  6. Click Add this Virtual Service.

Always On VPN IKEv2 Load Balancing with KEMP LoadMaster

Add Real Servers

  1. Expand Real Servers.
  2. Click Add New.
  3. Enter the IP address of the VPN server in the Real Server Address field.
  4. Click Add This Real Server.
  5. Repeat the steps above for each VPN server in the cluster.

Always On VPN IKEv2 Load Balancing with KEMP LoadMaster

Repeat all the steps above to create another virtual server using UDP port 4500.

Always On VPN IKEv2 Load Balancing with KEMP LoadMaster

Enable Layer 7 Operation

  1. Click View/Modify Services below Virtual Services in the navigation tree.
  2. Select the first virtual server and click Modify.
  3. Expand Standard Options.
  4. Uncheck Force L4.
  5. Check Transparency (additional configuration may be required – details here).
  6. Select Source IP Address from the Persistence Options drop-down list.
  7. Choose an appropriate value from the Timeout drop-down list.
  8. Choose an appropriate setting from the Scheduling Method drop-down list.
  9. Click Back.
  10. Repeat these steps on the second virtual server.

Always On VPN IKEv2 Load Balancing with KEMP LoadMaster

Enable Port Following

  1. Click View/Modify Services below Virtual Services in the navigation tree.
  2. Select the first virtual server and click Modify.
  3. Expand Advanced Properties.
  4. Select the virtual server using UDP 500 from the Port Following drop-down list.
  5. Click Back.
  6. Repeat these steps on the second virtual server.

Always On VPN IKEv2 Load Balancing with KEMP LoadMaster

Demonstration Video

The following video demonstrates how to enable IKEv2 load balancing for Windows 10 Always On VPN using the KEMP LoadMaster Load Balancer.

Summary

With the KEMP LoadMaster load balancer configured to use port following, Windows 10 Always On VPN clients using IKEv2 will be assured that their connections will always be delivered to the same back end VPN server, resulting in reliable load balancing for IKEv2 connections.

Additional Information

Windows 10 Always On VPN Certificate Requirements for IKEv2

Windows 10 Always On VPN Protocol Recommendations for Windows Server RRAS

Top 5 DirectAccess Troubleshooting Tips

Top 5 DirectAccess Troubleshooting TipsDirectAccess is a thing of beauty when everything is working as it should. When it isn’t, troubleshooting can be quite challenging. DirectAccess relies on many Windows platform technologies such as Active Directory for authentication, PKI for certificate management, group policy for settings deployment, IPsec for encryption, and IPv6 for transport. With so many dependencies, locating the source of the problem can be a difficult and daunting task.

I’m frequently called upon to help organizations of all sizes with DirectAccess troubleshooting. While this post is not intended to be a detailed, prescriptive guide for DirectAccess troubleshooting, I did want to share some common troubleshooting tips based on many years of troubleshooting DirectAccess.

Here are my top 5 DirectAccess troubleshooting tips:

  1. Check Prerequisites – Before diving in and collecting network traces and scouring event logs for clues as to why DirectAccess isn’t working, it’s essential to start at the beginning. Often the source of trouble is missing or misconfigured prerequisites. For example, is the DirectAccess client running a supported operating system? Remember, clients must be running Windows 10 Enterprise or Education, Windows 8.x Enterprise, or Windows 7 Enterprise or Ultimate. Also, ensure that the Windows firewall is enabled on DirectAccess servers and clients, that certificates are installed and valid (trusted, correct EKU, etc.), and that the DirectAccess settings GPO has been applied to servers and clients.
  2. Validate External Connectivity – If you are following implementation and security best practices for DirectAccess, the DirectAccess server will be in a perimeter/DMZ network behind an edge firewall. The firewall must be configured to allow inbound TCP port 443 only. If the firewall is also performing Network Address Translation (NAT), the NAT rule must be configured to forward traffic to the DirectAccess server’s dedicated or virtual IP address (VIP), or the VIP of the load balancer. Watch for routing issues when using load balancers too. It’s a good idea to confirm external connectivity using the Test-NetConnection PowerShell command. Even better, use the open source tool Nmap for more thorough testing.
  3. Remove Third Party Software – I can’t tell you how many times I’ve resolved DirectAccess connectivity issues by removing (not just disabling!) third party software on the client and/or server. It’s not uncommon for third-party security software to interfere with IPsec and/or IPv6 communication, both of which are vital to DirectAccess. If your DirectAccess troubleshooting efforts reveal no underlying issues with prerequisites or external connectivity, I’d suggest removing (at least temporarily) any third-party software and testing again.
  4. Isolate Environmental Issues – Occasionally other settings applied manually or via Active Directory group policy will interfere with DirectAccess. Examples include IPv6 being disabled in the registry, IPv6 transition technologies required to support DirectAccess are turned off, essential firewall rules for DirectAccess are disabled, or manipulating local security settings such as Access this computer from the network. To assist with troubleshooting it might be necessary to temporarily place DirectAccess clients and servers in their own dedicated Organizational Units (OUs) and block inheritance to isolate the configuration as much as possible. In addition, if DirectAccess clients are servers are provisioned using images or templates, testing with a clean build straight from the installation source (ISO or DVD) can be helpful.
  5. Check for Unsupported Configurations – If DirectAccess isn’t working, it might be possible the configuration you are trying to use is not supported. Examples including strong user authentication with OTP when force tunneling is enabled, provisioning Windows 7 clients when using Kerberos Proxy authentication, or provisioning Windows 10 clients when Network Access Protection (NAP) integration is enabled. These configurations won’t work and are formally documented here.

This is by no means a comprehensive or exhaustive troubleshooting guide. For more information and additional DirectAccess troubleshooting guidance I would encourage you to purchase my book Implementing DirectAccess with Windows Server 2016, which has an entire chapter devoted just to troubleshooting. In addition, watch my DirectAccess video training courses on Pluralsight for details and information about DirectAccess installation, configuration, management, support, and troubleshooting. And if you’re still struggling to resolve a DirectAccess problem, use the form at the bottom of this page to contact me to inquire about additional troubleshooting help.

Additional Resources

Microsoft Windows DirectAccess Client Troubleshooting Tool
DirectAccess and Windows 10 Professional
DirectAccess Troubleshooting with Nmap
DirectAccess Unsupported Configurations
Planning and Implementing DirectAccess with Windows Server 2016 Video Training Course on Pluralsight
Implementing DirectAccess with Windows Server 2016 Book

Need assistance with DirectAccess troubleshooting? Complete the form below and I’ll get in touch with you.

Microsoft Security Update MS13-064 and DirectAccess

With the August security update release cycle, Microsoft issued security bulletin MS13-064 to address a vulnerability in the Windows NAT driver that could result in a denial of service. The vulnerability could be exploited by an attacker who sends a specially crafted ICMP packet to the server running the Windows NAT Driver service. The vulnerability exists only on Windows Server 2012 and the affected driver, winnat.sys, is present when the DirectAccess role is installed. This vulnerability only affects only full installations of Windows Server 2012. Windows Server 2012 Core is not affected. If you are running DirectAccess on a full installation of Windows Server 2012, make sure you install this update as soon as possible to be protected from potential denial of service attacks. For more information about this update, click here. For a comprehensive list of updates that apply to DirectAccess on Windows Server 2012 as well as previous versions, please refer to Jason Jones’ DirectAccess hotfix summary page.