Windows RDP issues over VPN

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flimbar
Posts: 10
Joined: Sat Mar 13, 2021 8:04 am

Windows RDP issues over VPN

Post by flimbar » Mon May 03, 2021 5:58 am

I have made a LAN-to-LAN bridge using L3 IP routing as per the instructions here:
https://www.softether.org/4-docs/1-manu ... P_Routing)

It all seems to work fine, any machine on one network can access any machine on the other network.

However, Windows RDP connection between machines on the 2 networks doesn't work.
Connection to the RDP port 3389 is fine and you get a log in box and authenticates, it then says it is starting the session etc.. but then instead of the Windows desktop just a black screen appears and after a few seconds you get an error saying "the connection was lost".

I get exactly the same behaviour whether I use softether LAN-to-LAN IP routing or the openvpn equivalent set up i.e. everything works except Windows RDP, which sort of half works and then disconnects.

If I use a direct L2 bridge so that the VPN client is on the same network segment then it all works fine, the problem seems to be Windows RDP over a routed network. It also works fine if I port forward 3389 with an ssh connection.

I've seen lots of posts in forums saying "Windows RDP is a very simple protocol that just needs TCP to port 3389", so I don't understand what the issue is.

There's lots of tutorials saying that you can access RDP at a remote site using VPN, but they don't mention if they are using bridged or routed VPN, so my guess is that it is the former. I can't use bridged VPN because the 2 networks have different subnets.

This is driving me nuts, I've tried packet sniffing with wireshark to see what the difference is between a port-forwarded connection that works and a routed VPN connection that doesn't work and it looks like there is some UDP traffic that isn't getting through. The closest thing to my problem I've found is this ancient post on a cisco forum:
https://www.techrepublic.com/forums/dis ... ipsec-vpn/

I wonder if it is MTU issues? I had ssh connections that would drop if there was a lot of console output which I think is an MTU issue, I guess when the RDP connection is established there'll be a burst of a lot of data as the desktop is displayed? But then why does it work fine with a bridged connection?

WilburFrances
Posts: 1
Joined: Mon May 03, 2021 11:38 am

Re: Windows RDP issues over VPN

Post by WilburFrances » Mon May 03, 2021 11:40 am

yes, i have also faced same issue while accessing windows rdp vpn

solo
Posts: 65
Joined: Sun Feb 14, 2021 10:31 am

Re: Windows RDP issues over VPN

Post by solo » Mon May 03, 2021 12:08 pm

I use RDP over WireGuard which is a Layer 3 routed VPN. No problem.

May try it later with SoftEther L3.

flimbar
Posts: 10
Joined: Sat Mar 13, 2021 8:04 am

Re: Windows RDP issues over VPN

Post by flimbar » Sat May 08, 2021 6:20 am

So I'm getting the same issue with NoMachine, connections to port 4000 (NX port) work fine, but just like RDP the connection is established and then you just get a black screen until the connection times out.

nobody12
Posts: 47
Joined: Sat Feb 13, 2021 10:22 pm

Re: Windows RDP issues over VPN

Post by nobody12 » Sun May 09, 2021 7:06 am

I use softether with a L3 routed network (no nat/ Virtual NAT off). No problems with RDP here.

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