Connection keeps dropping with "UDP send error"

[sd43065]

I'm new to OpenVPN.

I already set up 2 OpenVPN servers on 2 Windows boxes and another 2 on Debian systems (one is a standalone box, the other runs in VirtualBox hosted in a Windows box).

I'm using OpenVPN Connect for Android to test server connections. It connects to those 2 in Windows boxes fine.

But it could not hold the connection with both Debian servers. Connection keeps dropping every 5 to 15 seconds.

I checked server log and could not see anything outstanding at all (no error or warning or anything). But on Android device, I could see the following sequence:

Code: Select all

......
... EVENT: CONNECTED info=...
... UDP send error: send: invalid argument
... EVENT: PAUSE trans=TO_DISCONNECTED
... EVENT: RESUME
... EVENT: RECONNECTING
......

I already googled for this error and failed to anything meaningful. So I readlly have no idea where to start to resolve this issue.

Any help would be greatly appreciated.

[ufergus]

I can't confirm the Windows part of the post, but I am experiencing the same behavior connecting to a debian server from my nexus 5. I can connect just fine, but after transferring a small amount of data my connection will drop out. I tried upgrading the server verison to 2.3.2 via wheezy-backports but there was no change in behavior. Any ideas?

[sd43065]

Hi, ufergus,

I'm still waiting for a solution or at least a way to test/diagnose the problem.

My OpenVPN servers are all on my home network. And I only have a Samsung S4 phone with OpenVPN Connect to test their connection through 4G.

With my Debian servers, I never get a chance to do any file transfer since connection gets dropped so often. However, I could browse some web pages while connected. So I believe my server configuration should be mostly correct.

When connected to servers running on Windows, it's quite stable with no frequent drops.

I originally thought, setting up and running OpenVPN on Linux should be easier than on Windows. Or at least it should provide more meaningful clue about connection issue.

The problem might very well be on the server side (need to tweak the configuration or something?). But since I only have OpenVPN Connect for testing connection and only it shows "UDP send error", I posted it here. Maybe I should have this posted on OpenVPN server forum instead.

[ufergus]

I did some testing with an mssfix value of 1300. It did improve my throughput but I still experienced the disconnect. The other thing I noticed was my 3G icon, which indicates a data connection, also disappears when I experience the disconnect. I am thinking the phone is dropping the data connection for some reason and OpenVPN then gets the UDP send error. What I don't understand is why the phone is dropping an active data connection. I know the nexus 5 uses a signal transmission path and periodically disconnects to scan for LTE but I wouldn't expect this to happen while a transfer is active. Maybe it only monitors tcp connections? What provider do you use?

[ufergus]

I was able to do a little more testing. I first put my phone in 3G mode, which 'should' prevent it from dropping a connection and searching for LTE. This did not change the disconnect behavior. I next did some testing in an area with an LTE signal. When connected to LTE, I did not experience the disconnect. I was able to load many webpages and even streamed a bit of netflix without an issue.