Duplicate Sessions - RAS v15.5 (build 15566)

We're seeing that RAS is allowing duplicate sessions to be created despite both the RAS gateway and necessary GPOs setup on the network. We have an engineering ticket open to look into this but haven't received a response in a quite a while (just called again today, support doesn't have access to development boards). I wanted to see if anyone else has noticed a similar problem:
RAS Gateway: Windows Server 2008 R2
RDP Hosts (x2): Windows Server 2008 R2
Gateway Config:
- Load Balancing > Limit User to one session per desktop (checked)
- Load Balancing > Reconnect to disconnected sessions (checked)
GPO:
- Computer Config > Policies > Admin Templates > Windows Components > Remote Desktop Services > Remote Desktop Session Host > Connections > Restrict Remote Desktop Services users to a single Remote Desktop Services session (enabled)

I reviewed all of GPOs and there's no conflicting polices that I can find.

 

I know this was nine years ago but did you end up getting a resolution for this? I'm having exactly the same issue in 2025.

 

I'm seeing this issue now more than ever. I thought it was the previous Parallels RAS update so last night I installed the latest, and already this morning I see two sessions. Oddly enough, the one that is connected is using transport protocol TCP and the other that is showing as disconnected is using UDP. Not sure if that is a clue or not.

 

So looking at my logon times, the active TCP connection is 8:34:21 and the UDP disconnected session is 8:36:03. That is a 1 minute, 42 second difference between session times. That kind of gap could be just enough for a timeout, fallback, or reconnection logic to kick in--especially if UDP is involved.

_____________________________________________
Not sure if this is the cause, since mine started happening recently, but Copilot mentioned this:

RDP uses both TCP and UDP starting with version 8 and beyond:
• TCP handles control traffic--keyboard, mouse, session management.
• UDP handles graphics and multimedia for better performance.
But here's the catch: UDP sessions are stateless and more prone to fragmentation, especially across VPNs or when MTU mismatches occur. If the client or gateway struggles to re-establish the UDP stream, it may spin up a new TCP session instead of reconnecting to the existing one--leading to the dual-session behavior you're seeing.

Recent Findings

• After updates to Windows Server 2022 or 2025, admins have reported RDP sessions defaulting to TCP due to UDP instability or policy changes.
• Some environments saw UDP sessions disconnecting randomly, while TCP stayed stable--resulting in a disconnected UDP session lingering while a new TCP session was created.
• A recent Microsoft update (e.g., KB5051987) appears to have altered how RDP prioritizes or falls back between protocols.

_____________________________________________

When I look at that KB, it states the following known issues:

Symptom
Remote desktop might freeze

After installing the January 2025 Windows preview update (KB5050094), released January 21, 2025, and later updates, on Windows 11, version 24H2 devices, you might experience Remote Desktop sessions freezing shortly after connection. When this issue occurs, mouse and keyboard input become unresponsive within the session, requiring you to disconnect and reconnect.

Remote desktop might disconnect

After installing the January 2025 Windows preview update (KB5050094) and later updates, users might experience unexpected disconnections with Remote Desktop Protocol (RDP) sessions, including Remote Desktop Services (RDS). We've observed a significant increase in reports of this issue following the release on the March 2025 Windows security update (KB5053598).

Users might notice their RDP sessions unexpectedly disconnecting after 65 seconds when establishing UDP-based connections from Windows 11, version 24H2 devices to RDS deployments running versions Windows Server 2016 or earlier. Resulting from this issue, users might experience frequent disconnections from their Remote Desktop and RDS sessions.

Note: Windows Server 2025 itself is not affected as an RDS host but might experience disconnects when acting as an RDP client connecting to older servers.
_____________________________________________

That KB above was released Feb 2025, but since then Copilot states the following post fixes:

Key Fixes Since February
1. March 2025 - KB5053598

• Intended to improve RDP stability, but ironically made the issues worse for many users.
• Microsoft acknowledged a spike in RDP disconnects and session hangs after this update.

2. June 2025 - KB5053656

• Claimed to fix RDP over UDP issues for Windows 11 24H2 and Server 2025.
• However, admins running Server 2019 reported that UDP sessions still failed, forcing them to revert to TCP-only for stability.

3. Emergency Server-Side Patch (March 26, 2025)

• Microsoft rolled out a server-side fix targeting Windows 11 24H2 environments where RDP sessions froze or failed to reconnect properly.
• This patch wasn't tied to a specific KB but was pushed silently to mitigate widespread complaints.

_____________________________________________

My RDP Servers are running Server 2022, and ai is suggesting that I force TCP-only transport via GPO. Not sure if anyone else has done that, but before I do that, I want to see if there is any way to set that preference in Parallels RAS itself.

 

I am going to change my site defaults to be TCP only, and see if that causes any issues and fixed this problem. The only drawback however is that UDP is more efficient, so hopefully this won't bite me ferformance wise.