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Remote Access Always On VPN Troubleshooting

Harmik Batth Tech's 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
    • 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
    • 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
  • 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

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

  • 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

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

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