About Point-to-Site VPN

A Point-to-Site (P2S) VPN gateway connection lets you create a secure connection to your virtual network from an individual client computer. A P2S connection is established by starting it from the client computer. This solution is useful for telecommuters who want to connect to Azure VNets from a remote location, such as from home or a conference. P2S VPN is also a useful solution to use instead of S2S VPN when you have only a few clients that need to connect to a VNet. This article applies to the Resource Manager deployment model.

What protocol does P2S use?

Point-to-site VPN can use one of the following protocols:

  • OpenVPN® Protocol, an SSL/TLS based VPN protocol. An SSL VPN solution can penetrate firewalls, since most firewalls open TCP port 443 outbound, which SSL uses. OpenVPN can be used to connect from Android, iOS (versions 11.0 and above), Windows, Linux and Mac devices (OSX versions 10.13 and above).

  • Secure Socket Tunneling Protocol (SSTP), a proprietary SSL-based VPN protocol. An SSL VPN solution can penetrate firewalls, since most firewalls open TCP port 443 outbound, which SSL uses. SSTP is only supported on Windows devices. Azure supports all versions of Windows that have SSTP (Windows 7 and later).

  • IKEv2 VPN, a standards-based IPsec VPN solution. IKEv2 VPN can be used to connect from Mac devices (OSX versions 10.11 and above).

Note

IKEv2 and OpenVPN for P2S are available for the Resource Manager deployment model only. They are not available for the classic deployment model.

How are P2S VPN clients authenticated?

Before Azure accepts a P2S VPN connection, the user has to be authenticated first. There are two mechanisms that Azure offers to authenticate a connecting user.

Authenticate using native Azure certificate authentication

When using the native Azure certificate authentication, a client certificate that is present on the device is used to authenticate the connecting user. Client certificates are generated from a trusted root certificate and then installed on each client computer. You can use a root certificate that was generated using an Enterprise solution, or you can generate a self-signed certificate.

The validation of the client certificate is performed by the VPN gateway and happens during establishment of the P2S VPN connection. The root certificate is required for the validation and must be uploaded to Azure.

Authenticate using Active Directory (AD) Domain Server

AD Domain authentication allows users to connect to Azure using their organization domain credentials. It requires a RADIUS server that integrates with the AD server. Organizations can also leverage their existing RADIUS deployment.       The RADIUS server could be deployed on-premises or in your Azure VNET. During authentication, the Azure VPN Gateway acts as a pass through and forwards authentication messages back and forth between the RADIUS server and the connecting device. So Gateway reachability to the RADIUS server is important. If the RADIUS server is present on-premises, then a VPN S2S connection from Azure to the on-premises site is required for reachability.      The RADIUS server can also integrate with AD certificate services. This lets you use the RADIUS server and your enterprise certificate deployment for P2S certificate authentication as an alternative to the Azure certificate authentication. The advantage is that you don’t need to upload root certificates and revoked certificates to Azure.

A RADIUS server can also integrate with other external identity systems. This opens up plenty of authentication options for P2S VPN, including multi-factor options.

Note

OpenVPN® Protocol is not supported with RADIUS authentication.

point-to-site

What are the client configuration requirements?

Note

For Windows clients, you must have administrator rights on the client device in order to initiate the VPN connection from the client device to Azure.

Users use the native VPN clients on Windows and Mac devices for P2S. Azure provides a VPN client configuration zip file that contains settings required by these native clients to connect to Azure.

  • For Windows devices, the VPN client configuration consists of an installer package that users install on their devices.
  • For Mac devices, it consists of the mobileconfig file that users install on their devices.

The zip file also provides the values of some of the important settings on the Azure side that you can use to create your own profile for these devices. Some of the values include the VPN gateway address, configured tunnel types, routes, and the root certificate for gateway validation.

Note

Starting July 1, 2018, support is being removed for TLS 1.0 and 1.1 from Azure VPN Gateway. VPN Gateway will support only TLS 1.2. Only point-to-site connections are impacted; site-to-site connections will not be affected. If you’re using TLS for point-to-site VPNs on Windows 10 clients, you don’t need to take any action. If you are using TLS for point-to-site connections on Windows 7 and Windows 8 clients, see the VPN Gateway FAQ for update instructions.

Which gateway SKUs support P2S VPN?

SKU S2S/VNet-to-VNet
Tunnels
P2S
SSTP Connections
P2S
IKEv2/OpenVPN Connections
Aggregate
Throughput Benchmark
BGP Zone-redundant
Basic Max. 10 Max. 128 Not Supported 100 Mbps Not Supported No
VpnGw1 Max. 30* Max. 128 Max. 250 650 Mbps Supported No
VpnGw2 Max. 30* Max. 128 Max. 500 1 Gbps Supported No
VpnGw3 Max. 30* Max. 128 Max. 1000 1.25 Gbps Supported No
VpnGw1AZ Max. 30* Max. 128 Max. 250 650 Mbps Supported Yes
VpnGw2AZ Max. 30* Max. 128 Max. 500 1 Gbps Supported Yes
VpnGw3AZ Max. 30* Max. 128 Max. 1000 1.25 Gbps Supported Yes

(*) Use Virtual WAN if you need more than 30 S2S VPN tunnels.

  • These connection limits are separate. For example, you can have 128 SSTP connections and also 250 IKEv2 connections on a VpnGw1 SKU.

  • Pricing information can be found on the Pricing page.

  • SLA (Service Level Agreement) information can be found on the SLA page.

  • VpnGw1, VpnGw2, VpnGw3, VpnGw1AZ, VpnGw2AZ and VpnGw3AZ are supported for VPN gateways using the Resource Manager deployment model only.

  • The Basic SKU is considered a legacy SKU. The Basic SKU has certain feature limitations. You can't resize a gateway that uses a Basic SKU to one of the new gateway SKUs, you must instead change to a new SKU, which involves deleting and recreating your VPN gateway. Verify that the feature that you need is supported before you use the Basic SKU.

  • Aggregate Throughput Benchmark is based on measurements of multiple tunnels aggregated through a single gateway. The Aggregate Throughput Benchmark for a VPN Gateway is S2S + P2S combined. If you have a lot of P2S connections, it can negatively impact a S2S connection due to throughput limitations. The Aggregate Throughput Benchmark is not a guaranteed throughput due to Internet traffic conditions and your application behaviors.

  • To help our customers understand the relative performance of VpnGw SKUs, we used publicly available iPerf and CTSTraffic tools to measure performances. Below table lists the results of performance tests using different algorithms. As you can see, the best performance is obtained when we used GCMAES256 algorithm for both IPsec Encryption and Integrity. We got average performance when using AES256 for IPsec Encryption and SHA256 for Integrity. When we used DES3 for IPsec Encryption and SHA256 for Integrity we got lowest performance.

SKU Algorithms
used
Throughput
observed
Packets per second
observed
VpnGw1 GCMAES256
AES256 & SHA256
DES3 & SHA256
650 Mbps
500 Mbps
120 Mbps
58,000
50,000
50,000
VpnGw2 GCMAES256
AES256 & SHA256
DES3 & SHA256
1 Gbps
500 Mbps
120 Mbps
90,000
80,000
55,000
VpnGw3 GCMAES256
AES256 & SHA256
DES3 & SHA256
1.25 Gbps
550 Mbps
120 Mbps
105,000
90,000
60,000
VpnGw1AZ GCMAES256
AES256 & SHA256
DES3 & SHA256
650 Mbps
500 Mbps
120 Mbps
58,000
50,000
50,000
VpnGw2AZ GCMAES256
AES256 & SHA256
DES3 & SHA256
1 Gbps
500 Mbps
120 Mbps
90,000
80,000
55,000
VpnGw3AZ GCMAES256
AES256 & SHA256
DES3 & SHA256
1.25 Gbps
550 Mbps
120 Mbps
105,000
90,000
60,000

Note

The Basic SKU does not support IKEv2 or RADIUS authentication.

What IKE/IPsec policies are configured on VPN gateways for P2S?

IKEv2

Cipher Integrity PRF DH Group
GCM_AES256 GCM_AES256 SHA384 GROUP_24
GCM_AES256 GCM_AES256 SHA384 GROUP_14
GCM_AES256 GCM_AES256 SHA384 GROUP_ECP384
GCM_AES256 GCM_AES256 SHA384 GROUP_ECP256
GCM_AES256 GCM_AES256 SHA256 GROUP_24
GCM_AES256 GCM_AES256 SHA256 GROUP_14
GCM_AES256 GCM_AES256 SHA256 GROUP_ECP384
GCM_AES256 GCM_AES256 SHA256 GROUP_ECP256
AES256 SHA384 SHA384 GROUP_24
AES256 SHA384 SHA384 GROUP_14
AES256 SHA384 SHA384 GROUP_ECP384
AES256 SHA384 SHA384 GROUP_ECP256
AES256 SHA256 SHA256 GROUP_24
AES256 SHA256 SHA256 GROUP_14
AES256 SHA256 SHA256 GROUP_ECP384
AES256 SHA256 SHA256 GROUP_ECP256
AES256 SHA256 SHA256 GROUP_2

IPsec

Cipher Integrity PFS Group
GCM_AES256 GCM_AES256 GROUP_NONE
GCM_AES256 GCM_AES256 GROUP_24
GCM_AES256 GCM_AES256 GROUP_14
GCM_AES256 GCM_AES256 GROUP_ECP384
GCM_AES256 GCM_AES256 GROUP_ECP256
AES256 SHA256 GROUP_NONE
AES256 SHA256 GROUP_24
AES256 SHA256 GROUP_14
AES256 SHA256 GROUP_ECP384
AES256 SHA256 GROUP_ECP256
AES256 SHA1 GROUP_NONE

What TLS policies are configured on VPN gateways for P2S?

TLS

Policies
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384
TLS_RSA_WITH_AES_128_GCM_SHA256
TLS_RSA_WITH_AES_256_GCM_SHA384
TLS_RSA_WITH_AES_128_CBC_SHA256
TLS_RSA_WITH_AES_256_CBC_SHA256

How do I configure a P2S connection?

A P2S configuration requires quite a few specific steps. The following articles contain the steps to walk you through P2S configuration, and links to configure the VPN client devices:

How do I remove the configuration of a P2S connection?

A P2S configuration can be removed using az cli and the following command :

az network vnet-gateway update --name <gateway-name> --resource-group <resource-group name> --remove "vpnClientConfiguration"

FAQ for native Azure certificate authentication

How many VPN client endpoints can I have in my Point-to-Site configuration?

It depends on the gateway SKU. For more information on the number of connections supported, see Gateway SKUs.

What client operating systems can I use with Point-to-Site?

The following client operating systems are supported:

  • Windows 7 (32-bit and 64-bit)
  • Windows Server 2008 R2 (64-bit only)
  • Windows 8.1 (32-bit and 64-bit)
  • Windows Server 2012 (64-bit only)
  • Windows Server 2012 R2 (64-bit only)
  • Windows Server 2016 (64-bit only)
  • Windows 10
  • Mac OS X version 10.11 or above
  • Linux (StrongSwan)
  • iOS

Note

Starting July 1, 2018, support is being removed for TLS 1.0 and 1.1 from Azure VPN Gateway. VPN Gateway will support only TLS 1.2. To maintain support, see the updates to enable support for TLS1.2.

Additionally, the following legacy algorithms will also be deprecated for TLS on July 1, 2018:

  • RC4 (Rivest Cipher 4)
  • DES (Data Encryption Algorithm)
  • 3DES (Triple Data Encryption Algorithm)
  • MD5 (Message Digest 5)

How do I enable support for TLS 1.2 in Windows 7 and Windows 8.1?

  1. Open a command prompt with elevated privileges by right-clicking on Command Prompt and selecting Run as administrator.

  2. Run the following commands in the command prompt:

    reg add HKLM\SYSTEM\CurrentControlSet\Services\RasMan\PPP\EAP\13 /v TlsVersion /t REG_DWORD /d 0xfc0
    reg add "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp" /v DefaultSecureProtocols /t REG_DWORD /d 0xaa0
    if %PROCESSOR_ARCHITECTURE% EQU AMD64 reg add "HKLM\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp" /v DefaultSecureProtocols /t REG_DWORD /d 0xaa0
    
  3. Install the following updates:

  4. Reboot the computer.

  5. Connect to the VPN.

Note

You will have to set the above registry key if you are running an older version of Windows 10 (10240).

Can I traverse proxies and firewalls using Point-to-Site capability?

Azure supports three types of Point-to-site VPN options:

  • Secure Socket Tunneling Protocol (SSTP). SSTP is a Microsoft proprietary SSL-based solution that can penetrate firewalls since most firewalls open the outbound TCP port that 443 SSL uses.

  • OpenVPN. OpenVPN is a SSL-based solution that can penetrate firewalls since most firewalls open the outbound TCP port that 443 SSL uses.

  • IKEv2 VPN. IKEv2 VPN is a standards-based IPsec VPN solution that uses outbound UDP ports 500 and 4500 and IP protocol no. 50. Firewalls do not always open these ports, so there is a possibility of IKEv2 VPN not being able to traverse proxies and firewalls.

If I restart a client computer configured for Point-to-Site, will the VPN automatically reconnect?

By default, the client computer will not reestablish the VPN connection automatically.

Does Point-to-Site support auto-reconnect and DDNS on the VPN clients?

Auto-reconnect and DDNS are currently not supported in Point-to-Site VPNs.

Can I have Site-to-Site and Point-to-Site configurations coexist for the same virtual network?

Yes. For the Resource Manager deployment model, you must have a RouteBased VPN type for your gateway. For the classic deployment model, you need a dynamic gateway. We do not support Point-to-Site for static routing VPN gateways or PolicyBased VPN gateways.

Can I configure a Point-to-Site client to connect to multiple virtual networks at the same time?

No. A Point-to-Site client can only connect to resources in the VNet in which the virtual network gateway resides.

How much throughput can I expect through Site-to-Site or Point-to-Site connections?

It's difficult to maintain the exact throughput of the VPN tunnels. IPsec and SSTP are crypto-heavy VPN protocols. Throughput is also limited by the latency and bandwidth between your premises and the Internet. For a VPN Gateway with only IKEv2 Point-to-Site VPN connections, the total throughput that you can expect depends on the Gateway SKU. For more information on throughput, see Gateway SKUs.

Can I use any software VPN client for Point-to-Site that supports SSTP and/or IKEv2?

No. You can only use the native VPN client on Windows for SSTP, and the native VPN client on Mac for IKEv2. However, you can use the OpenVPN client on all platforms to connect over OpenVPN protocol. Refer to the list of supported client operating systems.

Does Azure support IKEv2 VPN with Windows?

IKEv2 is supported on Windows 10 and Server 2016. However, in order to use IKEv2, you must install updates and set a registry key value locally. OS versions prior to Windows 10 are not supported and can only use SSTP or OpenVPN® Protocol.

To prepare Windows 10 or Server 2016 for IKEv2:

  1. Install the update.

    OS version Date Number/Link
    Windows Server 2016
    Windows 10 Version 1607
    January 17, 2018 KB4057142
    Windows 10 Version 1703 January 17, 2018 KB4057144
    Windows 10 Version 1709 March 22, 2018 KB4089848
  2. Set the registry key value. Create or set “HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RasMan\ IKEv2\DisableCertReqPayload” REG_DWORD key in the registry to 1.

What happens when I configure both SSTP and IKEv2 for P2S VPN connections?

When you configure both SSTP and IKEv2 in a mixed environment (consisting of Windows and Mac devices), the Windows VPN client will always try IKEv2 tunnel first, but will fall back to SSTP if the IKEv2 connection is not successful. MacOSX will only connect via IKEv2.

Other than Windows and Mac, which other platforms does Azure support for P2S VPN?

Azure supports Windows, Mac and Linux for P2S VPN.

I already have an Azure VPN Gateway deployed. Can I enable RADIUS and/or IKEv2 VPN on it?

Yes, you can enable these new features on already deployed gateways using Powershell or the Azure portal, provided that the gateway SKU that you are using supports RADIUS and/or IKEv2. For example, the VPN gateway Basic SKU does not support RADIUS or IKEv2.

Can I use my own internal PKI root CA to generate certificates for Point-to-Site connectivity?

Yes. Previously, only self-signed root certificates could be used. You can still upload 20 root certificates.

Can I use certificates from Azure Key Vault?

No.

What tools can I use to create certificates?

You can use your Enterprise PKI solution (your internal PKI), Azure PowerShell, MakeCert, and OpenSSL.

Are there instructions for certificate settings and parameters?

  • Internal PKI/Enterprise PKI solution: See the steps to Generate certificates.

  • Azure PowerShell: See the Azure PowerShell article for steps.

  • MakeCert: See the MakeCert article for steps.

  • OpenSSL:

    • When exporting certificates, be sure to convert the root certificate to Base64.

    • For the client certificate:

      • When creating the private key, specify the length as 4096.
      • When creating the certificate, for the -extensions parameter, specify usr_cert.

FAQ for RADIUS authentication

How many VPN client endpoints can I have in my Point-to-Site configuration?

It depends on the gateway SKU. For more information on the number of connections supported, see Gateway SKUs.

What client operating systems can I use with Point-to-Site?

The following client operating systems are supported:

  • Windows 7 (32-bit and 64-bit)
  • Windows Server 2008 R2 (64-bit only)
  • Windows 8.1 (32-bit and 64-bit)
  • Windows Server 2012 (64-bit only)
  • Windows Server 2012 R2 (64-bit only)
  • Windows Server 2016 (64-bit only)
  • Windows 10
  • Mac OS X version 10.11 or above
  • Linux (StrongSwan)
  • iOS

Note

Starting July 1, 2018, support is being removed for TLS 1.0 and 1.1 from Azure VPN Gateway. VPN Gateway will support only TLS 1.2. To maintain support, see the updates to enable support for TLS1.2.

Additionally, the following legacy algorithms will also be deprecated for TLS on July 1, 2018:

  • RC4 (Rivest Cipher 4)
  • DES (Data Encryption Algorithm)
  • 3DES (Triple Data Encryption Algorithm)
  • MD5 (Message Digest 5)

How do I enable support for TLS 1.2 in Windows 7 and Windows 8.1?

  1. Open a command prompt with elevated privileges by right-clicking on Command Prompt and selecting Run as administrator.

  2. Run the following commands in the command prompt:

    reg add HKLM\SYSTEM\CurrentControlSet\Services\RasMan\PPP\EAP\13 /v TlsVersion /t REG_DWORD /d 0xfc0
    reg add "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp" /v DefaultSecureProtocols /t REG_DWORD /d 0xaa0
    if %PROCESSOR_ARCHITECTURE% EQU AMD64 reg add "HKLM\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp" /v DefaultSecureProtocols /t REG_DWORD /d 0xaa0
    
  3. Install the following updates:

  4. Reboot the computer.

  5. Connect to the VPN.

Note

You will have to set the above registry key if you are running an older version of Windows 10 (10240).

Can I traverse proxies and firewalls using Point-to-Site capability?

Azure supports three types of Point-to-site VPN options:

  • Secure Socket Tunneling Protocol (SSTP). SSTP is a Microsoft proprietary SSL-based solution that can penetrate firewalls since most firewalls open the outbound TCP port that 443 SSL uses.

  • OpenVPN. OpenVPN is a SSL-based solution that can penetrate firewalls since most firewalls open the outbound TCP port that 443 SSL uses.

  • IKEv2 VPN. IKEv2 VPN is a standards-based IPsec VPN solution that uses outbound UDP ports 500 and 4500 and IP protocol no. 50. Firewalls do not always open these ports, so there is a possibility of IKEv2 VPN not being able to traverse proxies and firewalls.

If I restart a client computer configured for Point-to-Site, will the VPN automatically reconnect?

By default, the client computer will not reestablish the VPN connection automatically.

Does Point-to-Site support auto-reconnect and DDNS on the VPN clients?

Auto-reconnect and DDNS are currently not supported in Point-to-Site VPNs.

Can I have Site-to-Site and Point-to-Site configurations coexist for the same virtual network?

Yes. For the Resource Manager deployment model, you must have a RouteBased VPN type for your gateway. For the classic deployment model, you need a dynamic gateway. We do not support Point-to-Site for static routing VPN gateways or PolicyBased VPN gateways.

Can I configure a Point-to-Site client to connect to multiple virtual networks at the same time?

No. A Point-to-Site client can only connect to resources in the VNet in which the virtual network gateway resides.

How much throughput can I expect through Site-to-Site or Point-to-Site connections?

It's difficult to maintain the exact throughput of the VPN tunnels. IPsec and SSTP are crypto-heavy VPN protocols. Throughput is also limited by the latency and bandwidth between your premises and the Internet. For a VPN Gateway with only IKEv2 Point-to-Site VPN connections, the total throughput that you can expect depends on the Gateway SKU. For more information on throughput, see Gateway SKUs.

Can I use any software VPN client for Point-to-Site that supports SSTP and/or IKEv2?

No. You can only use the native VPN client on Windows for SSTP, and the native VPN client on Mac for IKEv2. However, you can use the OpenVPN client on all platforms to connect over OpenVPN protocol. Refer to the list of supported client operating systems.

Does Azure support IKEv2 VPN with Windows?

IKEv2 is supported on Windows 10 and Server 2016. However, in order to use IKEv2, you must install updates and set a registry key value locally. OS versions prior to Windows 10 are not supported and can only use SSTP or OpenVPN® Protocol.

To prepare Windows 10 or Server 2016 for IKEv2:

  1. Install the update.

    OS version Date Number/Link
    Windows Server 2016
    Windows 10 Version 1607
    January 17, 2018 KB4057142
    Windows 10 Version 1703 January 17, 2018 KB4057144
    Windows 10 Version 1709 March 22, 2018 KB4089848
  2. Set the registry key value. Create or set “HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RasMan\ IKEv2\DisableCertReqPayload” REG_DWORD key in the registry to 1.

What happens when I configure both SSTP and IKEv2 for P2S VPN connections?

When you configure both SSTP and IKEv2 in a mixed environment (consisting of Windows and Mac devices), the Windows VPN client will always try IKEv2 tunnel first, but will fall back to SSTP if the IKEv2 connection is not successful. MacOSX will only connect via IKEv2.

Other than Windows and Mac, which other platforms does Azure support for P2S VPN?

Azure supports Windows, Mac and Linux for P2S VPN.

I already have an Azure VPN Gateway deployed. Can I enable RADIUS and/or IKEv2 VPN on it?

Yes, you can enable these new features on already deployed gateways using Powershell or the Azure portal, provided that the gateway SKU that you are using supports RADIUS and/or IKEv2. For example, the VPN gateway Basic SKU does not support RADIUS or IKEv2.

Is RADIUS authentication supported on all Azure VPN Gateway SKUs?

RADIUS authentication is supported for VpnGw1, VpnGw2, and VpnGw3 SKUs. If you are using legacy SKUs, RADIUS authentication is supported on Standard and High Performance SKUs. It is not supported on the Basic Gateway SKU. 

Is RADIUS authentication supported for the classic deployment model?

No. RADIUS authentication is not supported for the classic deployment model.

Are 3rd-party RADIUS servers supported?

Yes, 3rd-party RADIUS servers are supported.

What are the connectivity requirements to ensure that the Azure gateway is able to reach an on-premises RADIUS server?

A VPN Site-to-Site connection to the on-premises site, with the proper routes configured, is required.  

Can traffic to an on-premises RADIUS server (from the Azure VPN gateway) be routed over an ExpressRoute connection?

No. It can only be routed over a Site-to-Site connection.

Is there a change in the number of SSTP connections supported with RADIUS authentication? What is the maximum number of SSTP and IKEv2 connections supported?

There is no change in the maximum number of SSTP connections supported on a gateway with RADIUS authentication. It remains 128 for SSTP, but depends on the gateway SKU for IKEv2. For more information on the number of connections supported, see Gateway SKUs.

What is the difference between doing certificate authentication using a RADIUS server vs. using Azure native certificate authentication (by uploading a trusted certificate to Azure).

In RADIUS certificate authentication, the authentication request is forwarded to a RADIUS server that handles the actual certificate validation. This option is useful if you want to integrate with a certificate authentication infrastructure that you already have through RADIUS.

When using Azure for certificate authentication, the Azure VPN gateway performs the validation of the certificate. You need to upload your certificate public key to the gateway. You can also specify list of revoked certificates that shouldn’t be allowed to connect.

Does RADIUS authentication work with both IKEv2, and SSTP VPN?

Yes, RADIUS authentication is supported for both IKEv2, and SSTP VPN. 

Does RADIUS authentication work with the OpenVPN client?

RADIUS authentication is not supported for the OpenVPN client.

Next Steps

"OpenVPN" is a trademark of OpenVPN Inc.