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Updated Question:

Note: Even the updated question is still misleading, please read the answer for the real issue.

I have a strange problem. I'm connected to my network via a VPN-SSL client (Fortigate). I can not access any machine via RDP directly through its IP address. It works only via a hostname (or domain name since it's a local domain environment). I can ping the systems via the VPN connection, as well as use other services (e.g. MSB) through the IP address. But clicking "connect" on the RDP-client (mstsc.exe) simply does nothing, not even an error message.

The VPN-network connection is routed, but as I said, other services work fine so I don't suspect a routing/firewall problem here. And I don't have any rules which apply specific to RDP connections (I'm talking about the Fortigate firewall appliance here, not the Windows firewall from the client. The Windows firewall on the LAN-client I'm trying to connect to is disabled).

Could there be some RDP server or client settings I missed? Any help would be appreciated.

Note: Using RDP via IP on a different machine/VPN-account works, so it could also be a problem with my local machine or VPN account. I'm using a faily up to date version of mstsc.exe (10.0.18362.1316).

Original Question:

I have a strange problem. I'm connected to my network via a VPN-SSL client (Fortigate). I set up a Win 10 test system which I want to access via RDP. I can ping the test system via the VPN connection, but clicking connect on the RDP-client (mstsc.exe) simply does nothing, not even an error message. Connecting via LAN (and not VPN) works fine. -> PLAESE NOTE UPDATE1: it does not work with any remote machine via IP

This seems to be RDP-protocol-specific (possible in connection with the VPN). I set up a second Linux test system with xRDP. Connecting via SSH through the VPN works fine. Connecting via RDP through the VPN results in the same problem. Connecting from the LAN works fine.

The VPN-network connection is routed, but as I said, the ping works fine so I don't suspect a routing/firewall problem here (I'm talking about the Fortigate firewall appliance here, not the Windows firewall from the test client. The windows firewall on the test client is disabled). Could there be some RDP server or client settings I missed? Any help would be appreciated.

Note: This is just via IP no DNS involved

Update1: I just realized the RDP behavior is persistent when I try to connect to any remote machine via IP from the VPN. But I can use the IP to establish file access etc. Also RDP works fine as long as I use the hostname/domain name (the LAN is a domain environment, so I use FQDNs: hostname.domainname.local). Strangely this problem does not appear on all the clients, using a different PC/VPN-account the problem goes away. I suppose I have to pinpoint it a little further. I'll try to access via IP the next time I'm physically connected via LAN.

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  • Is your remote end on the VPN on a different subnet than the target Windows 10 system? I think, depending on the particular VPN setup you could still ping.
    – anon
    Commented Dec 3, 2021 at 23:38
  • yes, different subnets but it should be routet via the Fortigate appliance. If we restrict it to a routing issue it's strange that routing works for Ping and SSH but not for RDP. At this point I think it's unlikely I can't rule it out completely. I could just try to ping the port via telnet, and see where it's getting me.
    – Albin
    Commented Dec 4, 2021 at 0:14
  • BTW, I set the routing/firewall policy so that traffic from the VPN to the LAN is allowed for all services.
    – Albin
    Commented Dec 4, 2021 at 0:29
  • are you trying to connect by hostname, fqdn, or ip, and do you notice any difference using IP? I usually have to use FQDNs to connect to systems on the other side of the VPN, and then it does rely on the VPNs vNic using the remote networks DNS server.
    – Frank Thomas
    Commented Dec 4, 2021 at 3:32
  • DNS is not the issue here, I'm connecting solely by IP, sorry, I should have mentioned that in the question.
    – Albin
    Commented Dec 4, 2021 at 12:30

1 Answer 1

Reset to default
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The problem was that I forgot that I added the autoreconnect parameter autoreconnect max retries:i:500 to the default.rdp file. Since it wasn't added to the RDP-files already existing on my system those still worked.

Compounding to the problem was, that I didn't notice that problem wasn't caused by the difference of using IPs or DNS names but between starting a new connection (through the default.rdp file) or an existing one (through the RDP file I created for this machine in the past).

Once I removed the line from the default.rdp file I could connect again.

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