Always On VPN IKEv2 Load Balancing with F5 BIG-IP

Always On VPN IKEv2 Load Balancing with F5 BIG-IPThe Internet Key Exchange version 2 (IKEv2) is the protocol of choice for Always On VPN deployments where the highest level of security is required. Implementing Always On VPN at scale often requires multiple VPN servers to provide sufficient capacity and to provide redundancy. Commonly an Application Delivery Controller (ADC) or load balancer is configured in front of the VPN servers to provide scalability and high availability for Always On VPN.

Load Balancing IKEv2

In a recent post I described some of the unique challenges load balancing IKEv2 poses, and I demonstrated how to configure the Kemp LoadMaster load balancer to properly load balance IKEv2 VPN connections. In this post I’ll outline how to configure IKEv2 VPN load balancing on the F5 BIG-IP load balancer.

Note: This article assumes the administrator is familiar with basic F5 BIG-IP load balancer configuration, such as creating nodes, pools, virtual servers, etc.

Initial Configuration

Follow the steps below to create a virtual server on the F5 BIG-IP to load balance IKEv2 VPN connections.

Pool Configuration

To begin, create two pools on the load balancer. The first pool will be configured to use UDP port 500, and the second pool will be configured to use UDP port 4500. Each pool is configured with the VPN servers defined as the individual nodes.

Always On VPN IKEv2 Load Balancing with F5 BIG-IP

Virtual Server Configuration

Next create two virtual servers, the first configured to use UDP port 500 and the second to use UDP port 4500.

Always On VPN IKEv2 Load Balancing with F5 BIG-IP

Persistence Profile

To ensure that both IKEv2 UDP 500 and 4500 packets are delivered to the same node, follow the steps below to create and assign a Persistence Profile.

1. Expand Local Traffic > Profiles and click Persistence.
2. Click Create.
3. Enter a descriptive name for the profile in the Name field.
4. Select Source Address Affinity from the Persistence Type drop-down list.
5. Click the Custom check box.
6. Select the option to Match Across Services.
7. Click Finished.

Always On VPN IKEv2 Load Balancing with F5 BIG-IP

Assign the new persistence profile to both UDP 500 and 4500 virtual servers. Navigate to the Resources tab on each virtual server and select the new persistence profile from the Default Persistence Profile drop-down list. Be sure to do this for both virtual servers.

Always On VPN IKEv2 Load Balancing with F5 BIG-IP

Additional Resources

Windows 10 Always On VPN IKEv2 Load Balancing with Kemp LoadMaster Load Balancer 

Windows 10 Always On VPN IKEv2 Security Configuration

Windows 10 Always On VPN and IKEv2 Fragmentation

Windows 10 Always On VPN Certificate Requirements for IKEv2

Video: Windows 10 Always On VPN Load Balancing with the Kemp LoadMaster Load Balancer

DirectAccess IP-HTTPS Preauthentication


Introduction

DirectAccess IP-HTTPS PreauthenticationRecently I’ve written about the security challenges with DirectAccess, specifically around the use of the IP-HTTPS IPv6 transition technology. In its default configuration, the DirectAccess server does not authenticate the client when an IP-HTTPS transition tunnel is established. This opens up the possibility of an unauthorized user launching Denial-of-Service (DoS) attacks and potentially performing network reconnaissance using ICMPv6. More details on this can be found here.

Mitigation

The best way to mitigate these security risks is to implement an Application Delivery Controller (ADC) such as the F5 BIG-IP Local Traffic Manager or the Citrix NetScaler. I’ve documented how to configure those platforms here and here.

No ADC?

For those organizations that do not have a capable ADC deployed, it is possible to configure the IP-HTTPS listener on the Windows Server 2012 R2 server itself to perform preauthentication.

Important Note: Making the following changes on the DirectAccess server is not formally supported. Also, this change is incompatible with one-time passwords (OTP)  and should not be performed if strong user authentication is enabled. In addition, null cipher suites will be disabled, resulting in reduced scalability and degraded performance for Windows 8.x and Windows 10 clients. Making this change should only be done if a suitable ADC is not available.

Configure IP-HTTPS Preauthentication

To configure the DirectAccess server to perform preauthentication for IP-HTTPS connections, open an elevated PowerShell command window and enter the following command.

ls Cert:\LocalMachine\My

DirectAccess IP-HTTPS Preauthentication

Copy the thumbprint that belongs to the SSL certificate assigned to the IP-HTTPS listener. Open an elevated command prompt window (not a PowerShell window!) and enter the following commands.

netsh http delete sslcert ipport=0.0.0.0:443
netsh http add sslcert ipport=0.0.0.0:443 certhash=[thumbprint]
appid={5d8e2743-ef20-4d38-8751-7e400f200e65}
dsmapperusage=enable clientcertnegotiation=enable

DirectAccess IP-HTTPS Preauthentication

For load-balanced clusters and multisite deployments, repeat these steps on each DirectAccess server in the cluster and/or enterprise.

Summary

Once these changes have been made, only DirectAccess clients that have a computer certificate with a subject name that matches the name of its computer account in Active Directory will be allowed to establish an IP-HTTPS transition tunnel connection.

DirectAccess Multisite Geographic Redundancy with Microsoft Azure Traffic Manager

Introduction

DirectAccess Multisite Geographic Redundancy with Microsoft Azure Traffic ManagerTo provide geographic redundancy, DirectAccess can be deployed in a multisite configuration. In this scenario, Windows 8.x and Windows 10 clients are aware of all entry points in the enterprise and will automatically select the nearest available entry point to connect to. The nearest entry point is defined as the one that responds the quickest. When a Windows 8.x or Windows 10 client attempts to establish DirectAccess connectivity, an HTTP GET is sent to all entry points and the client will select the one with the shortest Round Trip Time (RTT) for the request.

Note: Windows 7 clients can be provisioned when DirectAccess is configured for multisite access, but they must be assigned to an individual entry point.

Challenges

There are a number of challenges that come with the default multisite configuration. Choosing an entry point based solely on network latency is rather simplistic and can often produce unexpected results. It also lacks support for granular traffic distribution or active/passive configuration.

GSLB

DirectAccess Multisite Geographic Redundancy with Microsoft Azure Traffic ManagerFor the best experience, DirectAccess can be configured to use a Global Server Load Balancing (GSLB) solution to enhance transparent site selection and failover for Windows 8.x and Windows 10 clients. Commonly this is implemented using an on-premises appliance (Citrix NetScaler, F5 Global Traffic Manager, Kemp LoadMaster, A10 Thunder, etc.). These solutions offer exceptional control over DirectAccess traffic distribution, but they add expense and complexity.

Azure Traffic Manager

Azure Traffic Manager is a cloud-based GSLB solution that is a simple and cost-effective alternative to dedicated on-premises appliances. While it does not offer all of the features that GSLB appliances provide, it does provide better traffic distribution options than the default configuration. Importantly, it enables active/passive failover, which is a common requirement not supported natively with DirectAccess.

DirectAccess Multisite Geographic Redundancy with Microsoft Azure Traffic Manager

Traffic Manager Configuration

In the Azure portal (the new one, not the old one!) click New, Networking, and then Traffic Manager profile.

DirectAccess Multisite Geographic Redundancy with Microsoft Azure Traffic Manager

Provide a name and select a Routing method.

DirectAccess Multisite Geographic Redundancy with Microsoft Azure Traffic Manager

Routing method options are Performance, Weighted and Priority.

  • Performance. Select this option to enable clients to connect to the entry point with the lowest network latency.
  • Weighted. Select this option to enable clients to prefer some entry points more than others. Assign a weight value of 1 to 1000 for each entry point. Higher values have more preference. Values for entry points can be the same, if desired.
  • Priority. Select this option to enable clients to connect to a primary entry point, then fail over to a secondary or tertiary entry point in the event of an outage. Assign a priority value of 1 to 1000 for each entry point. Lower values take precedence. Each entry point must be assigned a unique priority value.

Click Create when finished. Next click Settings for the new traffic manager profile and click Configuration. Change Protocol to HTTPS, Port to 443, and Path to /IPHTTPS. Click Save when finished.

DirectAccess Multisite Geographic Redundancy with Microsoft Azure Traffic Manager

Next click Endpoints and click Add. Select External endpoint from the drop down list, provide a descriptive name, and then enter the Fully-Qualified Domain Name (FQDN) of the first DirectAccess entry point. When using the Performance routing method, choose a location that best represents the geography where the DirectAccess entry point is located. When using the Weighted or Priority routing methods, specify an appropriate value accordingly. Click Ok when finished. Repeat these steps for each entry point in the organization.

DirectAccess Multisite Geographic Redundancy with Microsoft Azure Traffic Manager

DirectAccess Configuration

In the Remote Access Management console, highlight DirectAccess and VPN below Configuration in the navigation tree and then click Configure Multisite Settings below Multisite Deployment in the Tasks pane. Click Global Load Balancing and choose Yes, use global load balancing. Enter the FQDN of the Azure Traffic Manager profile and click Next, and then click Commit.

DirectAccess Multisite Geographic Redundancy with Microsoft Azure Traffic Manager

Note: An SSL certificate with a subject name matching that of the GSLB FQDN is not required.

In some cases, the management console may report that global load balancing addresses cannot be identified automatically for some or all entry points.

DirectAccess Multisite Geographic Redundancy with Microsoft Azure Traffic Manager

If this occurs, it will be necessary to run the Set-DAEntryPoint PowerShell cmdlet to assign GLSB IP addresses to each entry point. The GSLB IP address is the public IPv4 address that the entry point public hostname resolves to.

Set-DAEntryPoint -Name [entrypoint_name] -GslbIP [external_ip_address]

For example:

Set-DAEntryPoint -Name "US West" -GslbIP 203.0.113.195
Set-DAEntryPoint -Name "US East" -GslbIP 198.51.100.21

Summary

DirectAccess includes native functionality to enable geographic load balancing for Windows 8.x and Windows 10 clients. The site selection process used by DirectAccess clients in this scenario is basic, and has the potential to yield unexpected results. Azure Traffic Manager is a simple, cost-effective alternative to dedicated on-premises GSLB appliances. It can be integrated with DirectAccess to address some of the shortcomings with the native entry point selection process.

Additional Resources

Configure F5 BIG-IP for DirectAccess NLS

Recently I wrote about the Network Location Server (NLS) and its importance for DirectAccess deployments. As I described previously, the NLS is nothing more than a web server with an SSL certificate installed. It should also be made highly available to prevent potential service disruption caused by planned or unplanned NLS server downtime. Any web server can serve as the NLS. In addition, if you have the F5 BIG-IP Local Traffic Manager (LTM) in your environment, you can easily configure the LTM to serve as the NLS.

To accomplish this, import the SSL certificate for the NLS and create an SSL client profile using its certificate and private key. Next, create a new iRule that contains the following code.

when HTTP_REQUEST {
HTTP::respond 200 
}

Configure F5 BGIP for DirectAccess NLS

Finally, create a new virtual server listening on TCP port 443 and assign this iRule as a resource for the virtual server. Once NLS reachability has been verified, update the DirectAccess configuration using the Remote Access Management console or the Set-DANetworkLocationServer PowerShell cmdlet.

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