Use RDP Multipath to improve connection reliability to Azure Virtual Desktop

Remote Desktop Protocol (RDP) Multipath improves session stability by continuously monitoring multiple network paths and dynamically selecting the most reliable one. This intelligent switching mechanism helps reduce the likelihood of disconnections and contributes to a smoother and more consistent user experience across different network conditions.

It offers several key benefits:

• Seamless integration: No configuration changes are needed beyond ensuring your environment supports RDP Shortpath.

• Intelligent path management: ICE discovers and evaluates multiple Remote Desktop Protocol (RDP) Shortpath routes using User Datagram Protocol (UDP) over STUN (Simple Traversal Underneath NAT) and TURN (Traversal Using Relays around NAT) protocols.

• Enhanced reliability: Backup paths remain on standby. If the active path becomes unstable or fails, RDP Multipath automatically switches to the next best path, reducing session drops and interruptions.

RDP Multipath uses multiple network paths to improve connection reliability. These paths can include combinations of UDP-based STUN or TURN connections when UDP connectivity is available, along with redundant TCP-based Reverse Connect paths established using Rendezvous.

If the main transport path becomes degraded or fails, the system automatically switches to a backup available UDP or TCP transport path. If all paths are lost—such as during a network outage—the system attempts to reconnect once network connectivity is restored. 

The following diagram illustrates how RDP Multipath works with Azure Virtual Desktop. In this user scenario, the primary active transport path is UDP via STUN, supplemented by redundant UDP connections through a TURN server.

When UDP‑based RDP Shortpath connectivity is available, UDP remains the preferred transport protocol for optimal performance and reliability. In addition to maintaining redundant UDP paths, Azure Virtual Desktop can establish redundant TCP standby transport paths to improve overall session resiliency.

Prerequisites

RDP Multipath works automatically when the following prerequisites are met:

• Ensure that RDP Shortpath is configured as the primary transport protocol. For more information, see Configure RDP Shortpath.

• Connections must be from a local Windows device using Windows App, version 2.0.559.0 or later. Other platforms aren't currently supported.

With the introduction of redundant TCP transport paths, users connecting over TCP can now also benefit from Multipath resiliency.

To experience redundant TCP‑based transport paths:

• Until the rollout reaches 100% availability, RDP Multipath with redundant TCP transport paths may not be consistently enabled across all host pools. Customers who want to enable the feature earlier can opt in their host pool to the Validation ring or enable it using the registry key.

• Connections must be from a local Windows device using Windows App Version 2.0.1069.0 or later.

Required network endpoints for RDP transport

To support RDP connectivity using UDP‑based Shortpath and Multipath, as well as TCP‑based connections over Reverse Connect, ensure outbound connectivity to the following endpoints:

Port scaling considerations

When using RDP Shortpath and RDP Multipath, customers should plan firewall and network capacity with per‑user port scaling in mind.

Each active user session can establish up to five outbound transport paths:

• Up to three UDP ports for UDP‑based RDP Shortpath and Multipath connections (for example, primary and redundant UDP paths discovered through STUN or TURN).

• Up to two TCP ports for TCP‑based RDP connections over Reverse Connect, including redundant TCP transport paths when available.

Ensure that firewall rules, NAT capacity, and port exhaustion limits are configured to accommodate the expected number of concurrent user sessions and their associated transport paths at scale.

Verify RDP Multipath connectivity

There are two ways to verify that RDP Multipath is being used for a connection:

• Users can check the connection status of a remote session from the connection bar, which shows RDP Multipath is enabled, as shown in the following example screenshot:

  

• Azure Virtual Desktop administrators can view connection reliability information in Azure Virtual Desktop Insights. For more information, see the connection reliability use case for Azure Virtual Desktop Insights.

  If you find some connections aren't using RDP Multipath, check that a firewall or other network restrictions doesn't block RDP Shortpath connections. A connection using STUN or TURN protocols is required.

Enable RDP Multipath with redundant TCP (opt in)

RDP Multipath with redundant TCP transport paths is being enabled through a phased, quality‑driven rollout. Until the rollout reaches full availability, the feature may not be consistently enabled across all host pools.

Customers who want to enable the feature ahead of full rollout can explicitly opt in on their session hosts using the registry key described below.

To enable RDP Multipath with redundant TCP transport paths, set the following registry key value to 100:

reg add "HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server\RdpCloudStackSettings" /v RendezvousActivationThreshold /t REG_DWORD /d 100 /f

Related content

To learn more about RDP Shortpath, see RDP Shortpath for Azure Virtual Desktop.