How do I troubleshoot connection problems with a license server?

Problem description: 

I am a license server administrator and have set up a license server for PLECS. When users try to start PLECS on a client computer, they receive one of the following errors:

  • Cannot connect to license server system.
  • License server machine is down or not responding.
  • The desired vendor daemon is down or not responding.
  • Cannot read data from license server system.
  • Invalid returned data from license server system.

The error messages listed above indicate that PLECS cannot communicate with the license manager and/or the vendor daemon running on the server computer. Possible reasons include:

  • The server machine is not running at all.
  • The license manager is not running.
  • A firewall blocks the communication between the client and the license manager.

The following steps enable you to pinpoint any of these problems.

Assert that the license server is actually running

Examine the debug log file of the license server. If you do not know what the debug log file is or where to find it, please review our installation instructions (for Windows and Linux).

If the license server has started successfully, you will see lines similar to these (summary log lines (SLOG) omitted):

12:32:10 (lmgrd) FlexNet Licensing (v11.13.1.3 build 176543 x64_n6) started on AMPERE (IBM PC)
12:32:10 (lmgrd) Copyright (c) 1988-2015 Flexera Software LLC. All Rights Reserved.
12:32:10 (lmgrd) World Wide Web:
12:32:10 (lmgrd) License file(s): C:\PLECS_License_Manager\plexim.lic
12:32:10 (lmgrd) lmgrd tcp-port 27000
12:32:10 (lmgrd) Starting vendor daemons ... 
12:32:10 (lmgrd) Starting vendor daemon at port 51112
12:32:10 (lmgrd) Using vendor daemon port 1702 specified in license file
12:32:10 (lmgrd) Started plexim (pid 2644)
12:32:10 (plexim) FlexNet Licensing version v11.13.1.3 build 176543 x64_n6
12:32:12 (plexim) Server started on AMPERE for:	plecsedit	
12:32:12 (plexim) EXTERNAL FILTERS are OFF
12:32:12 (lmgrd) plexim using TCP-port 51112

Verify that license manager and vendor daemon have been updated to the latest version published on our download page. (The license manager may also have a newer version e.g. if it is shared with another application.)

Take note of the port numbers highlighted in bold as you will need them further below.

If the debug log file reports a problem similar to the lines below, you need to address this problem first.

12:32:12 (lmgrd) plexim exited with status 34 (Invalid host)
12:32:12 (lmgrd) Please correct problem and restart daemons

Assert that the client license file points to the correct license server

The client file network.lic has the following syntax:

SERVER <licenseserver> ANY <port>

The placeholder <licenseserver> may be an IP address or a hostname — either a simple name or the fully qualified domain name (FQDN). If an IP address is used, verify that it is that of the license server. If a hostname is used, verify that the client computer can resolve the name to the IP address of the license server. This is done with the NSLOOKUP command in the Command Prompt on Windows, the Terminal app on macOS or a terminal on Linux:

> nslookup <licenseserver>
Server:  <something>
Address: <something>

Name:    <licenseserver>
Address: <IP address>

If you get the response Non-existent domain or NXDOMAIN, contact your network administrator for help or replace the hostname in the client license file with the IP address.

The placeholder <port> is optional. If it is omitted, the TCP port of lmgrd (as shown in the debug log file above) must be in the range 27000-27009. If <port> is given, it must match the TCP port of lmgrd.

Assert that the client computer can connect to the TCP ports used by the license server

Use the TELNET command on the client to check whether the client can connect to the TCP ports used by the license manager and the vendor daemon. On Windows, you may first need to enable the Telnet client (see Windows 7: Enabling Telnet Client or Windows 10: Enabling Telnet Client). Enter the following commands (replacing the numbers 27000 and 51112 with the actual TCP port numbers of lmgrd and plexim):

> telnet <IP address> 27000
> telnet <IP address> 51112

On Windows, a successful connection is indicated by the Command Prompt window going blank. Pressing Enter or Ctrl-C will terminate the connection.

On macOS and Linux, a successful connection will produce the following output:

Trying <IP address>...
Connected to <IP address>.
Escape character is '^]'.

Pressing Ctrl-C or Ctrl-] followed by the command quit will terminate the connection.

If instead you get an error Connection refused or Connect failed for either command, there is a problem in your computer network, most likely due to a firewall that blocks the connection. Please contact your network administrator for help.

Additional considerations

If all of the diagnostic steps above succeed and PLECS still reports connection errors, one of the following two cases might apply.

  • ​​Conflict with other license managers running on the same server
    If you are running multiple license managers with different software revisions on one server, it may happen that two license managers use the same TPC port number — one for IPv4 and the other for IPv6. In this situation, the PLECS client might always connect to the wrong license manager.
    To resolve the problem, use dedicated port numbers for the license manager lmgrd and the vendor daemon. For details please review the installation instructions (for Windows and Linux).
  • TPC timeout due to slow network communication
    By default, TCP connections between the client and the license server time out after 0.1 seconds. This may be too short if you have a slow network or if client and server are far apart. On Windows clients you can define an environment variable FLEXLM_TIMEOUT specifying the TPC timeout in microseconds.
    To increase the timeout to 1 second, set FLEXLM_TIMEOUT to 1000000.

Still need help?

If you still need help, send an email to

Please include the following information:

  • The server license file plexim.lic as installed on the license server
  • The license server debug log file
  • The client license file network.lic as installed on the client
  • The exact error message on the client
  • A protocol of the diagnostic steps described above