Troubleshooting client VPN tunnel connectivity

Purpose of this troubleshooting page

This page is specifically about attempting to find and resolve problems with an OpenVPN client program failing to connect to an OpenVPN Access Server. It does not deal with problems in reaching a target system over the established VPN tunnel once the VPN tunnel is already working. That is handled in a separate page: troubleshooting reaching systems over the VPN tunnel.

So if for example you start the OpenVPN client connection and it issues an error and disconnects you, then the information here should help you in determining a possible cause and solution. If not, reach out to us on the support ticket system and provide as much detail as you can.

Locating the server log files

To diagnose problems with an OpenVPN server or client, it is helpful to look at the log files. The log files are located in specific areas on your computer systems, and the following is a general guide on how to find them and how to get the best information out of them. Log files are the place to check whenever you're having any problems making a connection with an OpenVPN client program to the OpenVPN Access Server, they the information needed to ascertain what's going wrong.

On the OpenVPN Access Server there is the server side log:
/var/log/openvpnas.log /var/log/openvpnas.node.log (in case of a failover setup)

In the event that you are having problems with starting the Access Server or certain portions of it, for example the web services, then it may be useful to stop the Access Server service, move the log file aside, then start the Access Server service, and stop it again immediately. This creates a new clean log file that contains the startup and shutdown sequence of the Access Server and no other extraneous information. This makes analysis of the log file much easier. To do so use these commands in order:

service openvpnas stop
mv /var/log/openvpnas.log /var/log/openvpnas.log.old
service openvpnas start
service openvpnas stop

You can then grab the /var/log/openvpnas.log file for analysis and start the Access Server again:

service openvpnas start

Locating the client log files

Log file location for the OpenVPN Connect Client for Windows:
C:\Program Files (x86)\OpenVPN Technologies\OpenVPN Client\etc\log\openvpn_(unique_name).log

The OpenVPN Connect Client for Mac:
/Library/Application Support/OpenVPN/log/openvpn_(unique_name).log

Macintosh may not show you this folder in finder as it only shows you certain things and hides others. So to get to the /Library folder, open Finder and in the menu at the top choose Go followed by Go to folder and then enter the path /Library to get into that directory. You can then go to the correct folder and look up the log file. Please also note that the OpenVPN Connect Client for Macintosh will have permissions set on the log file so that you cannot normally open it. To bypass this, right click the log file and choose the Get info option in the menu. Then at the bottom, under Sharing & Permissions, you will be able to use the yellow padlock icon to unlock the settings and to give everyone read access. Then you will be able to open the log file with a right click and selecting Open with and then choosing something like Text editor to view the contents of the log file.

Known error messages and possible solutions

TLS Error: TLS key negotiation failed to occur within 60 seconds (check your network connectivity)

This particular error can have multiple different causes as it is a fairly generic error message.
A possible explanation is that the client program is old and supports only TLS 1.0, but the server is expecting TLS level 1.1 or higher. To see if this is the case log on to the server and check the server side log file. The chances are high that your client program is an older version, like version 2.2 or older, and that it doesn't know how to handle a modern TLS minimum level requirement, when you see messages that look like this on the server side:

OpenSSL: error:140760FC:SSL routines:SSL23_GET_CLIENT_HELLO:unknown protocol'
TLS_ERROR: BIO read tls_read_plaintext error'
TLS Error: TLS object -> incoming plaintext read error'
TLS Error: TLS handshake failed'
SIGUSR1[soft,tls-error] received, client-instance restarting'

The solution to this particular problem is to upgrade the client software to the latest version.
Another possible explanation is that the settings regarding TLS minimum requirement level have been altered but the OpenVPN client is using an older copy of the connection profile which has incorrect instructions. The settings on the client and the server must match for the connection to be successful. In this situation installing a new copy of the configuration profile will solve the issue. A complete uninstall, redownload, and reinstall of the OpenVPN Connect Client should take care of that for you.

And yet another possible explanation is that there is a blockade in place in a firewall or at the Internet service provider that is blocking or interfering with the TLS handshake in some way.

TLS Error: local/remote TLS keys are out of sync

For some reason the negotiated TLS key to be used on the client side for TLS encryption/decryption is different from the one used on the server side. That should never happen. When the client and server are talking to one another they agree upon a TLS key to be used for encrypting and decrypting traffic. By default in Access Server such a key is valid for 6 hours, and after those 6 hours, automatically the TLS refresh kicks in and they will agree upon a new key. There is a short overlap where both the old and new key are accepted, until the old key is expired and the new key must be used. If for some reason one side doesn't do this, you see this error message.

A possible cause is a bug in the OpenVPN protocol with the version used in OpenVPN Connect Client which was resolved, where the automatic TLS key refresh would fail because the client and server couldn't agree properly on the encryption cipher to use. So if you encounter this particular problem and you are using an OpenVPN3 based client like OpenVPN Connect Client 2.*, then consider updating to the latest version. You can do so for example per computer by downloading OpenVPN Connect Client for Windows or OpenVPN Connect Client for macOS from our website, and installing it. However a better solution would be to update your Access Server to the latest version so that you get the updated Connect Client embedded in there, and then downloading and installing the latest version of OpenVPN Connect Client from your Access Server. If you use other client software and it shows problems, try finding a newer version for it. Worst case scenario, you could also consider changing the TLS key refresh to something larger in the Advanced VPN page of the Admin UI, to avoid triggering the issue. This does of course lower security somewhat.

Server poll timeout

One of the very first steps that an OpenVPN client program will do when trying to connect to an OpenVPN Access Server is to simply send out a message requesting for a reply. So basically a "hello are you there?" message. The server is then supposed to respond and then a connection is started. However if you see a server poll timeout error message then the server could not be reached at the specified port. Why this is not possible is another question entirely, but the error message is very clear: there is simply no response at all on that address and port. So when you see this message it would be good to check if the port is actually open, if the port is correct, if the address you're trying to reach can actually be reached from the Internet, and isn't a private IP address only, and other such checks to confirm basic connectivity to the server. At this point you're not even looking at a problem that has anything to do with the OpenVPN protocol itself. This is a most basic "this server cannot be reached" message.

A common mistake that is made is that people set up the Access Server on a private IP address but neglect to set up a proper FQDN DNS name for it, and configure that FQDN DNS name in the Admin UI under Server Network Settings in the Host name or IP address field. It is that field value that connection profiles generated and provisioned to the OpenVPN clients will be using to start a connection to. So if this is set to an internal private IP address that the Access Server was installed on, then the connection profiles will try to connect to that private IP address, which is unlikely to be reachable from anywhere else but the internal network that the Access Server itself is on. The solution is to set up a proper DNS name and configure that and save settings. Then uninstall, redownload, and reinstall the connection profile or OpenVPN Connect Client program and to try again.

Another common mistake is to forget to open the 3 ports required for OpenVPN Access Server to be reachable properly. By default these are TCP 443, TCP 943, and UDP 1194.

SESSION_ID only allowed to be used by client IP address that created it

OpenVPN Access Server uses a session-based-token system for server-locked and user-locked profiles. Auto-login type profiles don't. What this means is that after a user authenticates successfully, they are given a session token to identify themselves with. Compare it to going to a party and you show up and pay your entry fees, and if you need to go out for a little bit, they give you a stamp on the back of your hand, or put a paper/plastic strip around your wrist, so that you can show up again later and be admitted access again. That's a very simplified explanation. With a session token, each token is unique and uniquely identifies you. This avoids having to store your credentials in memory or bothering the user to reauthenticate when you temporarily lose contact with the server and reconnect again, so it's safer and more convenient. The session token is locked to the IP address that the original authentication attempt was made from, this is a security feature. When you see this message it means the session token your client program offered to the server was generated originally from another IP address. This can happen for example if you switch Internet connection, like logging in at work, then moving your laptop home and it tries to reconnect automatically with the session token. This session token IP lock is a security feature that can be disabled to allow such automatic reconnects to occur without this error message.

Authentication Error: Session: your session has expired, please reauthenticate

The OpenVPN Access Server works with a session token based authentication system when you are using a server-locked or user-locked profile. When you authenticate successfully, you are given a session token instead. The session token identifies you now from that moment onward. By default the session token expires after 5 minutes of inactivity as in not being connected to the server, and it also expires after 24 hours by default. Furthermore, when the session token is generated on the server, it gets locked to the VPN client's connecting IP address. This session IP lock can be disabled, and the timeout for session inactivity and the timeout for total session duration mentioned can also be adjusted. If for example you are on your phone and you are connected through WiFi, and you walk out of range of WiFi, and it switches to another Internet connection like 3G/4G or something, then your VPN client will disconnect but attempt to reconnect automatically. Your IP will now be different and as such the session token is not valid anymore. You will see an error like in the previous section in the server side log file (SESSION_ID only allowed to be used by client IP address that created it). And if your connection has lasted 24 hours in total, then it will also disconnect you if you're on a session-based connection with server-locked or user-locked profile. The solution is to either use an auto-login type profile or to increase the session token duration.

unable to obtain session ID from, ports=443: (error description here)

This error message can be found in the capi.log file and also shown in the popup message in Windows or macOS when you use OpenVPN Connect Client for Windows or macOS. This error message indicates that a server-locked connection profile is being used, which is the default on OpenVPN Access Server when you download and install the OpenVPN Connect Client. A server-locked connection profile is designed to be user-agnostic, meaning it doesn't carry any user-identifiable information in it, and is a sort of universal profile. This allows any valid user accounts to start a connection with this OpenVPN Connect Client. The credentials are passed over a secure HTTPS channel to the XML-RPC services of the Access Server for verification, and if approved, the client will receive a copy of the user-locked profile for this user, and a session token. Those will be used to start the OpenVPN tunnel. After the tunnel is disconnected, the user-locked profile and session token are deleted. But for this to work, there must be a working HTTPS connection to the web services of the Access Server.

unable to obtain session ID from, ports=443:
Other SSL errors:[('SSLroutines','SSL23_READ','ssl handshake failure')]

This could indicate that the Connect Client was able to reach some service, but it does not appear to be the Access Server web services, or perhaps the traffic is mangled by some firewall or proxy solution. For example we have seen situations where OpenVPN Access Server was installed with default settings, and OpenVPN Connect Client was installed and working, and then the port was changed on the server side from TCP 443, to TCP 444 for example, and then a web server was setup on that same server system, with an HTTPS website running on it on port TCP 443. The OpenVPN Connect Client won't have received an update to the new port setting for the Access Server web services, and so it tries to talk to the old port, where now a web server runs. This causes an unexpected problem that can result in this type of error. If you encounter this problem you should investigate if the port that the client is trying to reach is actually reachable by this client, and to try to determine if there really is an Access Server web service running there. If you changed the ports on the server you need to reinstall this client so it updates the settings.

unable to obtain session ID from, ports=443:
ConnectionRefusedError: 10061: No connection could be made because the target machine actively refused it

This is a very clear indication that the address and port that the OpenVPN Connect Client is trying to reach, does not have an Access Server web service running there. For example if you install OpenVPN Connect Client on a client computer, and then you go to the Access Server and change the ports that it listens to, then the client will still be trying to connect to the old ports that were originally configured. This can also sometimes occur if the address of your server is simply misconfigured. The solution is making sure that in the Admin UI in the Network Settings page you have set the address that your server can be reached at correctly (it is best to do a DNS name instead of an IP) and that the ports are how you want them, and then after that's set up, to download and install the OpenVPN Connect Client on your client computers.

unable to obtain session ID from, ports=443:
XML-RPC: TimeoutError

This indicates that the Access Server web interface's XML-RPC interface is unreachable. The OpenVPN Connect Client uses this interface to obtain the necessary certificates and configuration to start the OpenVPN connection when you are using a server-locked profile. You will not be needing the XML-RPC interface when you use user-locked and auto-login profiles. The advantage of server-locked profiles is that they are universal - any valid user at the Access Server can log in and connect. The timeout error just means the connection timed out, usually a firewall or such is blocking the connection. The solution is to ensure that the web interface is reachable from this OpenVPN client, or instead use a user-locked or auto-login type profile.

unable to obtain session ID from, ports=443:
XML-RPC function GetSession with 1 arguments may not be called at the configured relay level

The OpenVPN Connect Client program for Windows and macOS by default uses server-locked profiles. These contain only the information necessary to talk to the XML-RPC web interface of the Access Server for the purpose of authenticating a user and obtaining the required certificates and connection information to start the OpenVPN tunnel. This is done so this client is universal. It will work for all valid users on the server and isn't locked to a specific user. This does require that the web interface is reachable and that under client settings in the Admin UI the XML-RPC function is set to at least limited functionality. Full functionality also works, but when you set this to disabled, then you will get this error. The solution is to either stop using server-locked profiles and switch to user-locked or auto-login profiles, or to enable at least limited functionality for XML-RPC calls. The default is limited functionality and that is sufficient for OpenVPN Connect Client and server-locked profiles.

See the logfile 'C:\Program Files (x86)\OpenVPN Technologies\OpenVPN Client\core\ovpntray.exe.log' for details

If you see this error message while launching the OpenVPN Connect Client, and it fails to launch, you may be missing specific Microsoft Visual C++ Redistributable DLL library files. This issue was resolved in OpenVPN Connect Client for Windows version by adding specific required library files into the OpenVPN Connect Client program directories. You should ensure you use up-to-date software to resolve this issue. You can upgrade your Access Server to the latest version so that it offers updated OpenVPN Connect Client software, or you can separately download the OpenVPN Connect Client for Windows from our website, to upgrade your existing Connect Client version.

Serial number not found in DB

OpenVPN Access Server by default comes with an internal PKI structure, which means a self-signed root certificate with unique certificates generated for each OpenVPN client for that server. These are all unique and tied together. This is part of the strength of OpenVPN, the identity of a VPN client and a VPN server are verified in both directions when a connection is made. The client verifies the server, and the server verifies the client. So for each user account you add to the Access Server, a unique certificate is generated. The certificate is bound to the user account name, so you can't log in with the credentials for user bob with the certificates for user billy. Each certificate also has a serial number, a unique number identifying the certificate. If you see the error that the serial number is not found in the database, that means this certificate is not known to this server. Even if you revoke a certificate, it is still known to the server, and will not produce this particular error. So you may be using a certificate from a completely different Access Server by mistake, or maybe you started with a new setup of Access Server on your server and the certificates are wiped and new ones generated for the new setup, while you're still using old certificates from the previous installation. To resolve this problem, make sure to delete the wrong connection profile from your client computer and obtain a new one from your current Access Server installation and use that to connect.

Open TAP device "" PATH="" FAILED TUN Error: cannot acquire TAP handle EVENT: TUN_IFACE_CREATE cannot acquire TAP handle [FATAL-ERR] 2021 EVENT: DISCONNECTED Client exception in transport_recv: tun_exception: not connected

You may receive this error message when the OpenVPN Connect 3.x service stops or does not resume when you sign back into the computer. The issue is likely caused by an antivirus program. Specifically, we’ve seen this with ESET Antivirus. You can reconnect by restarting the service manually, but the automatic connection may still encounter the issue. To test, turn off ESET. If that resolves the issue, then you may want to open a support ticket with ESET.

See also the topic authentication problems for more possible error messages and solutions regarding authentication issues.