Limit to number of connections via port forwarding ?

[cpn42]

Hello. I'm using VirtualBox 5.2.18 on Windows 7 host.
I created a NAT network with a port forwarding to an OpenVPN server on this network. I need to connect many clients to this server in order to perform network tests. Every time I launch my clients they stop connecting after the 128th. If I kill one of them and launch a 129th, it connects like a charm. If I try to connect a 129th with the 128 other still running, my OpenVPN server doesn't see anything, no incoming connection, no error, just nothing.
So I'm asking myself, is there a limit to the port forwarding number of simultaneous clients ? I tried to have a look at the source code but didn't see anything relevant. Do someone has an answer please ?
Thanks a lot for helping.

[socratis]

Are you sure it's not OpenVPN that imposes the limit?

[cpn42]

I just tested directly (without NAT) with 200 clients and everything works perfectly. So OpenVPN is not the problem. I continue to investigate.

[socratis]

We need to see a complete VBox.log, from a complete VM run:

• Start the VM from cold-boot (not from a paused or saved state) / Observe error / Shutdown the VM (force close it if you have to).
• With the VM completely shut down (not paused or saved), right-click on the VM in the VirtualBox Manager and select "Show Log".
• Save only the first "VBox.log", ZIP it and attach it to your response. See the "Upload attachment" tab below the reply form.

[cpn42]

Here it is.
Thanks a lot for helping.

[socratis]

I just tested directly (without NAT) with 200 clients and everything works perfectly

When you mean "directly" what exactly do you mean? Which networking mode did you use?

[cpn42]

I put my clients on the same NAT network than the server and I could connect more than 200 clients simultaneously. So the problem is not from OpenVPN.

[socratis]

I put my clients on the same NAT network than the server

I'm sorry, but I still will need a clarification on this, as I don't "get it". What does it mean "on the same NAT network"? As opposed to what exactly? Do you have any numbers/ranges?

You know, I focused on the last aspects of the logs last time, and I didn't do a thorough analysis. This time, while trying to refresh my memory, I did. And I (re)discovered the following issues:

00:00:00.859033 [/Devices/e1000/0/LUN#0/] (level 4)
00:00:00.859034   Driver <string>  = "IntNet" (cb=7)
00:00:00.859035 
00:00:00.859035 [/Devices/e1000/0/LUN#0/Config/] (level 5)
00:00:00.859035   IfPolicyPromisc      <string>  = "deny" (cb=5)
00:00:00.859036   IgnoreConnectFailure <integer> = 0x0000000000000000 (0)
00:00:00.859036   Network              <string>  = "HostInterfaceNetworking-Intel(R) Ethernet Connection (2) I219-V" (cb=64)

That's not NAT anything, that's Bridged networking!!! Where is the NAT that you're referring to? It's neither "NAT", nor "NATnetwork"!

00:00:00.859062 [/Devices/hpet/0/Config/] (level 4)
00:00:00.859063   ICH9 <integer> = 0x0000000000000001 (1)

Why, oh why are you using something that is declared as experimental, and for OSX guests only? Please explain that to me, with a sentence that makes sense if you can...

00:00:00.859189 VRamSize <integer> = 0x0000000001000000 (16 777 216, 16 MB)

I would max the VRAM. You can never have enough VRAM...

[vincen57]

Hello,

I allow to relaunch this topic because I have exactly the same problem.

If I configure one or more Virtualbox VMs with a connection in "nat network" mode, I cannot exceed 127 incoming connections for all VMs.
The system queues additional connections until the total number of connections is less than 127.

Is this a bug or a license restriction from Oracle?

[socratis]

I allow to relaunch this topic because I have exactly the same problem.

How about re-reading it and providing some logs and information. A "me too" won't get you far...

[vincen57]

Hello,

Here are the logs of the concerned VM.

I have performed more in-depth tests and have made the following observation:
- Only the "Nat Network" mode is limited to 127 simultaneous connections
- NAT" and "Bridged Network" modes have no such limits
- The problem is not related to port forwarding

So the solution to my problem is to use the "NAT" mode instead of "Nat Network".

I would also like to point out that this problem appears on all types of network protocols (MySQL, HTTP,...)