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Remote Access Always On VPN Troubleshooting

Harmik Batth Tech Blog

Remote Access Always On VPN Troubleshooting

You can troubleshoot connection issues in several ways. For client-side issues and general troubleshooting, the application logs on client computers are invaluable. For authentication-specific issues, the NPS log on the NPS server can help you determine the source of the problem.

The application logs on client computers record most of the higher-level details of VPN connection events.

Look for events from source RasClient. All error messages return the error code at the end of the message. Some of the more common error codes are detailed below, but a full list is available in Routing and Remote Access Error Codes.

  • Error description. The remote connection was not made because the attempted VPN tunnels failed. The VPN server might be unreachable. If this connection is attempting to use an L2TP/IPsec tunnel, the security parameters required for IPsec negotiation might not be configured properly.
  • Possible cause. This error occurs when the VPN tunnel type is Automatic and the connection attempt fails for all VPN tunnels.
  • Possible solutions:
    • If you know which tunnel to use for your deployment, set the type of VPN to that particular tunnel type on the VPN client side.
    • By making a VPN connection with a particular tunnel type, your connection will still fail, but it will result in a more tunnel-specific error (for example, “GRE blocked for PPTP”).
    • This error also occurs when the VPN server cannot be reached or the tunnel connection fails.
  • Make sure:
    • IKE ports (UDP ports 500 and 4500) aren’t blocked.
    • The correct certificates for IKE are present on both the client and the server.
  • Error description. The connection was prevented because of a policy configured on your RAS/VPN server. Specifically, the authentication method the server used to verify your user name and password may not match the authentication method configured in your connection profile. Please contact the administrator of the RAS server and notify him or her of this error.
  • Possible causes:
    • The typical cause of this error is that the NPS has specified an authentication condition that the client cannot meet. For example, the NPS may specify the use of a certificate to secure the PEAP connection, but the client is attempting to use EAP-MSCHAPv2.
    • Event log 20276 is logged to the event viewer when the RRAS-based VPN server authentication protocol setting doesn’t match that of the VPN client computer.
  • Possible solution. Ensure that your client configuration matches the conditions that are specified on the NPS server.
  • Error description. The network connection between your computer and the VPN server could not be established because the remote server is not responding. This could be because one of the network devices (e.g., firewalls, NAT, routers) between your computer and the remote server is not configured to allow VPN connections. Please contact your administrator or your service provider to determine which device may be causing the problem.
  • Possible cause. This error typically occurs when a firewall between the client and the server blocks the ports that the VPN tunnel uses.
  • Possible solution. Ensure that UDP ports 500 and 4500 are allowed through all firewalls between the client and the RRAS server.
  • Error description. IKE failed to find a valid machine certificate. Contact your network security administrator about installing a valid certificate in the appropriate certificate store.
  • Possible cause. This error typically occurs when no machine certificate or root machine certificate is present on the VPN server.
  • Possible solution. Ensure that the certificates outlined in this document are installed on both the client computer and the VPN server.
  • Error description. IKE authentication credentials are unacceptable.
  • Possible causes. This error typically occurs in one of the following cases:
    • The machine certificate used for IKEv2 validation on the RAS server doesn’t have Server Authentication under Enhanced Key Usage.
    • The machine certificate on the RAS server has expired.
    • The root certificate to validate the RAS server certificate isn’t present on the client computer.
    • The VPN server name used on the client computer doesn’t match the subjectName of the server certificate.
  • Possible solution. Verify that the server certificate includes Server Authentication under Enhanced Key Usage. Verify that the server certificate is still valid. Verify that the CA used is listed under Trusted Root Certification Authorities on the RRAS server. Verify that the VPN client connects by using the FQDN of the VPN server as presented on the VPN server’s certificate.
  • Error description. The server certificate does not have Server Authentication as one of its certificate usage entries.
  • Possible cause. This error may occur if no server authentication certificate is installed on the RAS server.
  • Possible solution. Make sure that the machine certificate the RAS server uses for IKEv2 has Server Authentication as one of the certificate usage entries.

Generally, the VPN client machine is joined to the Active Directory–based domain. If you use domain credentials to log on to the VPN server, the certificate is automatically installed in the Trusted Root Certification Authorities store. However, if the computer is not joined to the domain or if you use an alternative certificate chain, you may experience this issue.

  • Error description. A certificate chain processed but terminated in a root certificate that the trust provider does not trust.
  • Possible cause. This error may occur if the appropriate trusted root CA certificate is not installed in the Trusted Root Certification Authorities store on the client computer.
  • Possible solution. Make sure that the root certificate is installed on the client computer in the Trusted Root Certification Authorities store.

NPS accounting logs are created and stored by NPS. By default, these are stored in %SYSTEMROOT%\System32\Logfiles\ in a file named INXXXX.txt, where XXXX is the date the file was created.

By default, these logs are in comma-separated values format, but they don’t include a heading row. The heading row is:



If you paste this heading row as the first line of the log file, then import the file into Microsoft Excel, the columns will be properly labeled.

The NPS logs can be helpful in diagnosing policy-related issues. For more information about NPS logs, see Interpret NPS Database Format Log Files.

Comments: 2

  1. Michel says:

    I get error 13801,

    What could be the issue if the error only happen for one user on the remote workstation who’s trying to connect? And Other users can still connect to the IKEv2 VPN with the same workstation!!!


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