Troubleshooting inability to check out network license over VPN on MacOS 10.14

[Anonymous]

Reposting this in a different forum per maxim_k's recommendation.

I'm our small-lab IT support/admin trying to get people set up to check out shared licenses over a VPN, and hit a wall.  We are a mixed Mac/Windows shop, and I've been focusing on Mac clients to start with.

I'm suspecting that the VPN is blocking some traffic on some ports, but our main IT department is overwhelmed so I'm trying to make sure I haven't overlooked anything, or that there aren't troubleshooting steps I've failed to try.

Environment:  Single MacOS 10.12 server running flexlm (port 27000), attempting to pull license with MacOS 10.14 client connected to office network via current version of GlobalProtect. Client is running AutoCAD Mac 2018.

What happens:  Autocad appears to hang when I enter the network address for multi-user license server.  After a VERY long delay (tens of minutes), AutoCAD will eventually throw a "Network license not available" error with varying error codes.

I've tried with and without the port specified, and identifying the server by short network name ("host"), full network name ("host.domain.edu"), and IP address; all behave identically.  I had another user test and apparently the behavior is the same on Windows, so this may not be a Mac-specific problem.

No firewalls on either end, just what the VPN is doing (which I don't have visibility into).  The license server pings fine, and I can connect to it via other protocols (ssh, screen sharing).  Doing a port scan, 2080 and 27000 both show open, as expected; adjacent ports don't.

It of course works fine from within the office network for both Mac and Windows clients.

I'm not very good at reading Wireshark network captures, but as best I can tell it's connecting on 27000, then when it tries to connect on 2080 some of the traffic is getting dropped, since I'm seeing re-sent packets.

I'm guessing all of the above is pointing toward the VPN system blocking some traffic on 2080, but does anyone have suggestions of what I might try to either confirm this or rule out other configuration issues?

[Mark.Lancaster]

@Anonymous 

For Windows, its most likely related to this https://synergiscadblog.com/2020/03/19/working-from-home-with-autodesk-vpn/

See @TravisNave response here for mac https://forums.autodesk.com/t5/autodesk-desktop-app/flex-lm-timeout-setting-for-autocad2018-for-mac/m-p/8450408#M1993

[Anonymous]

Thank you for the link to that thread. I had seen the timeout increase instructions for Windows but had failed to find where to adjust that on MacOS.

However, even with that variable set to 5000000 the results are exactly the same.

[Anonymous · Accepted solution]

The problem was indeed VPN-side firewall issues. I wasn't told exactly what was changed that fixed it, but the firewall appeared to be blocking some traffic on port 2080, causing apparent hangs without an immediate error message.

Apparently increasing the timeout was not necessary in this case, but knowing how to set that variable on MacOS is very useful.